Chapter XI: Literature and History (33)

As we derive _Acanthochiasma_ from _Acanthometron_ by concrescence in pairs of the twenty radial spines, the Müllerian law of Icosacantha must be employed also to the ten diametral spines of the former, therefore two of them are equatorial, four tropical, and four polar spines. In the same way we may employ the new law of disposition found in the thirty-two radial spines of _Actinastrum_ equally to the sixteen diametral spines of _Chiastolus_, which we derive from the former, four of them are equatorial, eight tropical, and four polar spines (compare above, p. 732).

_The Central Capsule_ of the Chiastolida is spherical, and exhibits in general the same shape as in the #Acanthonida#, and specially in the Astrolonchida. Of course every diametral spine pierces the capsule twice, at two points diametrically opposed. In some species of _Acanthochiasma_ the central capsule is formed very late, so that it seems often to be absent. A very accurate description of the capsule and its nucleus, as well as of the calymma and the pseudopodia, is given by Richard Hertwig in his Organismus der Radiolarien (1879, pp. 10-18). The pseudopodia are very numerous, and sometimes bear reddish granules.

{738}_Synopsis of the Genera of Chiastolida._

I. Subfamily Chiastolidina. Sixteen diametral
spines, derived by concrescence of thirty-two
radial spines, 321. _Chiastolus_.

II. Subfamily Acanthochiasmida. Ten diametral
spines, derived by concrescence of twenty
radial spines, 322. _Acanthochiasma_.

Genus 321. _Chiastolus_,[361] n. gen.

_Definition._--#Chiastolida# with sixteen diametral spines, derived from thirty-two radial spines opposite and grown together in pairs.

The genus _Chiastolus_, hitherto known only by a single observed specimen, comprises the Chiastolida with sixteen diametral spines, which are loosely crossed in the centre of the body. Four of these spines are equatorial, four polar, and eight tropical. We derive _Chiastolus_ from _Actinastrum_ by concrescence of every two opposite spines in one axis of the body (compare above, pp. 729, 732).

1. _Chiastolus amphicopium_, n. sp. (Pl. 129, figs. 3, 3_a_, 3_b_).

Spines in the central part cylindrical, spirally convoluted in a very peculiar manner, broadened towards both ends, strongly compressed, two-edged; the broadest parts are the two truncated distal ends, five to seven times as broad as the thinnest central part, which is placed between two spindle-shaped intumescences. These cochleary central parts of the sixteen spines seem to be resting one upon another. Each spine (composed of two opposite equal radial spines) has nearly the form of a double oar. The single observed specimen (preserved in glycerine) exhibited a most regular disposition of the thirty-two spines (grown together in pairs in the centre). The diameter of the dark non-transparent spherical central capsule equalled one-fifth to one-fourth of the total length of the double spines. When the soft parts of the body were destroyed by sulphuric acid, the sixteen single spines were suddenly dispersed.

_Dimensions._--Length of the sixteen double spines 0.5, distal breadth (of the truncated ends) 0.05, central breadth 0.01; diameter of the central capsule 0.12.

_Habitat._--South-east Pacific (near Juan Fernandez), Station 297, surface.

Genus 322. _Acanthochiasma_,[362] Krohn, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.

_Definition._--#Chiastolida# with ten diametral spines, derived from twenty radial spines opposite and grown together in pairs.

{739}The genus _Acanthochiasma_ with a small number of common species, comprises the Chiastolida with ten diametral spines, which are loosely crossed in the centre of the body. I could distinguish only four species, two of which are cosmopolitan and very widely distributed. In all four species the diametral spines are quite simple, cylindrical; only in one species distinguished by a spiral winding or torsion in the middle part, where they are crossed one to another. We derive _Acanthochiasma_ from _Acanthometron_ by concrescence of every two spines opposite in one axis of the body.

1. _Acanthochiasma krohnii_, Haeckel.

_Acanthochiasma krohnii_, Haeckel, 1862, Monogr. d. Radiol., p.403, Taf.
xix. fig. 7.

_Acanthochiasma krohnii_, R. Hertwig, 1879, Organismus d. Radiol., Taf.
ii. fig. 6.

Spines needle-shaped, cylindrical, very thin and long, of equal breadth in their whole length, distinguished by a high degree of elasticity. Central capsule colourless or yellowish-white, transparent. Granules of the sarcode colourless.

_Dimensions._--Length of the spines 0.5 to 1.0, breadth 0.001 to 0.002.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, very common.

2. _Acanthochiasma rubescens_, Krohn.

_Acanthochiasma rubescens_, Haeckel, 1862, Monogr. d. Radiol., p. 403.

Spines cylindrical, of equal breadth in their whole length, not very elastic, pointed at the two ends. Central capsule intransparent, reddish, with violin-shaped concretions. Granules of the sarcode red coloured.

_Dimensions._--Length of the spines 0.2 to 0.6, breadth 0.004 to 0.006.

_Habitat._--North Atlantic, Madeira, Krohn; Lanzerote, Haeckel.

3. _Acanthochiasma fusiforme_, Haeckel.

_Acanthochiasma fusiforme_, Haeckel, 1862, Monogr. d. Radiol., p. 404,
Taf. xix. fig. 8.

Spines spindle-shaped, from the thicker central part thinned towards the two thin conical ends, perfectly straight and smooth, rigid, inelastic. Central capsule non-transparent, brown.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the central part 0.006 to 0.009.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific.

4. _Acanthochiasma spirale_, n. sp.

Spines spindle-shaped, tapering from the thicker central part towards the two thin conical ends, rigid, inelastic; their central part is spirally convoluted in a very peculiar cochlea-like manner, as in _Chiastolus amphicopium_ (Pl. 129, figs. 3_a_, 3_b_). The ten spines are propped one upon another by the central screw. Central capsule dark, opaque.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth of the central spiral part 0.01.

_Habitat._--Central Pacific, Station 266, surface.

{740}----

Suborder II. ACANTHONIDA, Haeckel (Pls. 130-132).

_Acanthonida_, Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Acanthometra# with twenty radial spines, disposed according to the Müllerian or Icosacanthan law in five zones each of four spines.

Family XXXVI. #ASTROLONCHIDA#, Haeckel (Pl. 130).

_Astrolonchida_, Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Acanthometra# with twenty radial spines of nearly equal size and similar form, disposed according to the law of the Icosacantha. No lattice-shell.

The family #Astrolonchida#, the first and oldest of the #Acanthonida#, is no doubt the ancestral stock not only of this suborder but also all #Acanthophracta#, _i.e._, of all Icosacantha or all ACANTHARIA in which twenty radial spines are regularly disposed according to the Müllerian law, forming five zones each of four alternating spines (compare above, p. 717). The Astrolonchida differ from the #Acanthophracta# in the absence of a complete lattice-shell, from the other two families of #Acanthonida# (the Quadrilonchida and Amphilonchida) in the equal size and similar form of all the spines. Probably this equality is nowhere quite perfect, since in all Icosacantha the central bases of the twenty spines exhibit originally certain slight differences of form and junction, effected by the regular disposition itself. But setting aside this slight difference, only recognisable by means of a very accurate investigation of the central junction (and in thinner spines often not at all recognisable), the twenty spines of the Astrolonchida appear perfectly equal. Therefore the four equatorial spines are not distinguished from the sixteen other spines, as is constantly the case in the two following families.

The number of genera (eleven) and of species (seventy-six) in the Astrolonchida is far larger than in the five other families of #Acanthometra#, and requires a distinction into three different subfamilies. (A) In the Zygacanthida the form of the radial spines is quite simple, without apophyses or transverse processes; (B) in the Phractacanthida each spine bears two opposite apophyses (rarely two longitudinal rows of these opposite apophyses); (C) in the Stauracanthida each spine bears a cross of four apophyses, opposite in pairs (rarely four longitudinal crossed rows of apophyses, opposite in pairs). The Phractacanthida and Stauracanthida appear as two divergent branches of the pedigree, derived independently from the common ancestral stock of Zygacanthida.

In the Zygacanthida, constantly devoid of apophyses, we can distinguish only three genera, characterised by the different fundamental form of the radial spines; these are:--(1) _Acanthometron_, with cylindrical or conical spines (without edges); (2) _Zygacantha_, with compressed and two-edged spines; (3) _Acanthonia_, with four-edged, prismatic or pyramidal spines. The transverse section of the spines is in the first case {741}circular, in the second elliptical or lanceolate, in the third square. All the different forms of spines, which we find in the numerous ACANTHARIA, may be reduced to these three forms, and among these the second and third are derived from the first.

The development of apophyses or of lateral transverse processes (wanting in the Zygacanthida) is of the greatest value for the further differentiation of the ACANTHARIA. For from the Phractacanthida (with two opposite apophyses on each spine) we must derive the Phrastaspida, the common ancestral stock of the Diporaspida (and therefore also the Belonaspida, Hexalaspida, Diploconida, and Phractopeltida). On the other hand the Stauracanthida (with four crossed apophyses on each spine) have produced the Stauraspida, or the ancestral group of the Tessaraspida and Sphærocapsida. From all these #Acanthophracta#, possessing a complete lattice-shell, the Astrolonchida differ in the absence of such a complete shell. Also in the few cases in which the apophyses become latticed (_Doracantha_ among the Phractacanthida, and _Phatnacantha_ among the Stauracanthida), the lattice-plates of the neighbouring spines never meet with their edges, as is the case in all #Acanthophracta#. But in a phylogenetic as well as in an ontogenetic sense the former are the ancestral stock of the latter.

_The Central Capsule_ in the Astrolonchida is commonly spherical, sometimes with twenty roundish elevations or conical papillæ, extending radially to the basal half of the radial spines. The calymma is voluminous, and forms around the radial spines conical or cylindrical "jelly-sheaths," which are connected with the spines by coronas of Myophrisca (or of the bodies formerly called "Gallert-cilien," afterwards recognised as "contractile Filamente").

_Synopsis of the Genera of Astrolonchida._

-------------------------------------------------------------------------
I. Subfamily Zygacanthida.
Twenty radial spines simple, without apophyses or lateral transverse
processes.
-------------------------------------------------------------------------
Spines cylindrical, with circular transverse
section, 323. _Acanthometron_.

Spines compressed, two-edged or lamellar, with
elliptical or rhomboidal transverse section, 324. _Zygacantha_.

Spines quadrangular (prismatic or pyramidal), with
four edges, with square transverse section, 325. _Acanthonia_.

-------------------------------------------------------------------------
II. Subfamily Phractacanthida.
Twenty radial spines provided each with two opposite apophyses (or
two longitudinal rows of apophyses).
-------------------------------------------------------------------------
{ Apophyses simple, 326. _Lithophyllium_.
{
Two apophyses opposite on { Apophyses branched, 327. _Phractacantha_.
each spine. {
{ Apophyses latticed, 328. _Doracantha_.

Two opposite longitudinal rows of apophyses (four
to eight or more apophyses on each spine,
opposite in pairs), 329. _Astrolonche_.
-------------------------------------------------------------------------
III. Subfamily Stauracanthida.
Twenty radial spines provided each with four crossed apophyses (or
four crossed longitudinal rows of apophyses).
-------------------------------------------------------------------------
{ Apophyses simple, 330. _Xiphacantha_.
Four apophyses (in cross {
form) opposite in pairs { Apophyses branched, 331. _Stauracantha_.
on each spine. {
{ Apophyses latticed, 332. _Phatnacantha_.

Four longitudinal rows of apophyses, opposite in
pairs in cross form on each spine, 333. _Pristacantha_.

{742}Subfamily 1. ZYGACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with twenty simple radial spines, without apophyses or lateral transverse processes.

Genus 323. _Acanthometron_,[363] J. Müller, 1855, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 229.

_Definition._--#Astrolonchida# with simple cylindrical or needle-shaped radial spines, without edges and without apophyses; their transverse section is circular.

The genus _Acanthometron_, with the restricted definition here given, is the most simple form of all #Acanthonida#, and may be regarded as the common ancestral form not only of this suborder but also of all #Acanthophracta#, in general of all Icosacantha, or all ACANTHARIA in which twenty radial spines are regularly disposed after the Müllerian law (p. 717). In the wider sense, given originally to #Acanthometra# by Johannes Müller, its discoverer, this genus comprised all ACANTHARIA constituting here our order "#Acanthometra#" (Radiolaria without lattice-shell, with radial spines united in the centre). In my Monograph (1862, p. 375) I restricted this genus to those "Acanthometrida" in which twenty simple spines of equal size (and without apophyses) are supported one upon another in the centre, and I separated as _Astrolithium_ those forms in which they are grown together in the centre. But this difference now appears not so important, and I restrict here the genus _Acanthometron_ (not #Acanthometra#) to those most simple forms in which the simple radial spines are cylindrical or conical, without edges.

Subgenus 1. _Acanthometrella_, Haeckel.

_Definition._--Spines at the central base without leaf-cross, united by the opposed triangular faces of their pyramidal bases, resting one upon another.

1. _Acanthometron elasticum_, Haeckel.

_Acanthometra elastica_, Haeckel, 1862, Monogr. d. Radiol., p. 376, Taf.
xv. fig. 1, Taf. xviii. fig. 1.

_Acanthometra elastica_, R. Hertwig, 1879, Organismus d. Radiol., Taf. i.
figs. 2, 2_a_, 2_b_.

Spines cylindrical, very thin and long, needle-shaped, at the central base four-sided pyramidal, without leaf-cross. Distal apex conical. The spines are very elastic, of nearly equal thickness in their whole length. Central capsule quite pellucid, colourless, with a variable number of yellow pigment-bodies (xanthellæ?).

_Dimensions._--Length of the spines 0.3 to 0.6, breadth 0.001 to 0.002.

_Habitat._--Cosmopolitan, very common in all warmer seas; Mediterranean, Atlantic, Indian, Pacific, surface.

{743}2. _Acanthometron cylindricum_, n. sp. (Pl. 130, fig. 2).

Spines cylindrical, thick and long, at the central base thickened with a pear-shaped knob, and with very small central fulcral pyramid, without leaf-cross. Distal apex rounded or truncated. Central capsule opaque, filled with red pigment-bodies.

_Dimensions._--Length of the spines 0.4 to 0.8, breadth 0.01 to 0.015.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

3. _Acanthometron fuscum_, J. Müller.

_Acanthometra fusca_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 47, Taf. xi. fig. 4.

_Acanthometra fusca_, Haeckel, 1862, Monogr. d. Radiol, p. 377.

Spines very thin and long, in the proximal half cylindrical, in the distal half conical, gradually thinned towards the simple conical apex. Central base a small four-sided pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth 0.002 to 0.004.

_Habitat._--Mediterranean (Cette, Portofino, Messina).

4. _Acanthometron bulbosum_, Haeckel.

_Acanthometra bulbosa_, Haeckel, 1862, Monogr. d. Radiol., p. 377, Taf.
xv. fig. 2, Taf. xviii fig. 2.

Spines very thin and long, cylindrical, with simple needle-shaped apex; in the basal part conical, towards the centre much thickened, with a short four-sided fulcral pyramid, without leaf-cross. Central capsule opaque, filled with brown pigment-bodies.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the middle and outer part 0.001, in the basal part 0.008 to 0.012.

_Habitat._--Mediterranean; Atlantic, Station 354, surface.

5. _Acanthometron dolichoscion_, Haeckel (Pl. 129, figs. 6-8).

_Acanthometra dolichoscia_, Haeckel, 1862, Monogr. d. Radiol., p. 377,
Taf. xviii. figs. 3_a_, 3_b_.

Spines very long and thin, cylindrical, in the thickened outer half about twice as thick as in the thin inner half, at the simple apex compressed, two-edged. Central base little thickened, with a small four-sided pyramid, without leaf-cross. Central capsule transparent, whitish or yellowish.

_Dimensions._--Length of the spines 0.6 to 0.8, breadth in the proximal part 0.004, in the distal part 0.008.

_Habitat._--Mediterranean (Messina, Portofino), surface.

6. _Acanthometron conicum_, n. sp.

Spines short and thick, conical, gradually thinner from the thick conical base towards the simple apex. Central part of the base with a large fulcral pyramid, but without leaf-cross. Central capsule transparent, colourless (?).

_Dimensions._--Length of the spines 0.08 to 0.12, basal breadth 0.02.

_Habitat._--North Pacific, Station 244, surface.

{744}7. _Acanthometron pellucidum_, J. Müller.

_Acanthometra pellucida_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 47, Taf. xi. figs. 1-3.

_Acanthometra pellucida_, Haeckel, 1862, Monogr. d. Radiol., p. 378.

Spines cylindrical, very thin and long, needle-shaped, nearly of equal thickness in their whole length. Central base with a small fulcral pyramid, without leaf-cross. Distal apex bifid or bifurcate, with two thin parallel teeth. Central capsule pellucid, colourless, with yellow pigment-bodies. (Differs from _Acanthometron elasticum_ mainly in the bifid apex.)

_Dimensions._--Length of the spine 0.1 to 0.3, breadth 0.002 to 0.004.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

8. _Acanthometron wageneri_, Haeckel.

_Acanthometra wageneri_, Haeckel, 1862, Monogr. d. Radiol., p. 378.

Spines cylindrical, in the thickened outer half about twice as broad as in the thin inner half. Central base a little thickened, with large fulcral pyramid, but without leaf-cross. Distal apex bifid, with two divergent, often denticulated teeth. Central capsule pellucid, with yellow pigment-bodies. (Differs from _Acanthometron dolichoscion_ mainly in the bifid apex.)

_Dimensions._--Length of the spines 0.2 to 0.5, breadth in the inner part 0.003, in the outer 0.006.

_Habitat._--Adriatic Sea; Triest, Wagner; Corfu, Haeckel, surface.

Subgenus 2. _Phyllostaurus_, Haeckel, 1862, Monogr. d. Radiol., p. 381.

_Definition._--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of the neighbouring lamellæ are propped one upon another in such a manner that there are formed twenty-two hollow pyramidal spaces or compartments (compare p. 721).

9. _Acanthometron siculum_, Haeckel.

_Acanthometra sicula_, Haeckel, 1862, Monogr. d. Radiol., p. 382, Taf.
xvii. figs. 1, 2; Taf. xviii. fig. 8.

Spines elongate, conical, tapering gradually from the thick base towards the simple distal apex. Conical circular base supported by a basal leaf-cross of double the breadth. Central capsule yellowish-brown, opaque.

_Dimensions._--Length of the spines 0.3 to 0.4, basal breadth 0.008 to 0.012, leaf-cross 0.024.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

{745}10. _Acanthometron catervatum_, Haeckel.

_Acanthometra brevispina_, Haeckel, 1862, Monogr. d. Radiol., p. 382,
Taf. xv. fig. 5, Taf. xviii. fig. 9.

Spines cylindrical, nearly of equal breadth throughout their whole length. Apex either simple, conical, or bifid. Base with a large leaf-cross, four to six times as broad as the spine itself. Central capsule transparent, yellow. The Atlantic specimens have much longer spines than those figured from the Mediterranean, but are otherwise not different. Therefore I have changed the inconvenient name _brevispinum_ into _catervatum_.

_Dimensions._--Length of the spines 0.1 to 0.3, breadth 0.005 to 0.008; basal leaf-cross 0.02 to 0.032.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 354, Gulf Stream (Færöe Channel) in great abundance, John Murray, surface.

Subgenus 3. _Astrolithium_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 810.

_Definition._--Spines in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin; a star with twenty equal rays.

11. _Acanthometron bulbiferum_, n. sp. (Pl. 130, fig. 1).

_Astrolithium bulbiferum_, Haeckel, 1881, Prodromus, p. 466.

Spines needle-shaped, cylindrical, very thin and long, with simple apex; suddenly thickened and forming a broad regular cone at the central base; all twenty conical bulbs have their broad bases grown together and forming a central icosahedron of acanthin; from its twenty faces arise the circular bases of the cones in regular disposition.

_Dimensions._--Length of the spines 0.2 to 0.5, breadth 0.001 to 0.003; height of the basal cones 0.06, basal breadth of them 0.02.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

12. _Acanthometron bifidum_, Haeckel.

_Astrolithium bifidum_, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf.
xx. fig. 5.

Spines needle-shaped, cylindrical, of equal breadth in their whole length. Distal apex bifid, with two parallel straight teeth. Central bases of all twenty spines grown perfectly together and forming a central sphere of acanthin. Central capsule brown opaque.

_Dimensions._--Length of the spines 0.2, breadth 0.003.

_Habitat._--Mediterranean (Messina), Haeckel, surface.

{746}Genus 324. _Zygacantha_,[364] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 51.

_Definition._--#Astrolonchida# with simple, compressed, and two-edged radial spines, without apophyses; their transverse section is elliptical or rhomboidal.

The genus _Zygacantha_ comprised in the original definition of J. Müller only a single species, _Zygacantha furcata_, distinguished from the other #Acanthometra# by forked spines with two long parallel teeth. It seems now advisable to unite in this genus all those Astrolonchida in which the simple spines are two-edged, compressed, or leaf-shaped. The term _Zygacantha_ may be conceived as the general expression of the important fact, that in all Icosacantha the twenty spines are opposite in pairs.

Subgenus 1. _Zygacantharium_, Haeckel.

_Definition._--Spines at the central base without leaf-cross and without hollow pyramidal compartments, united by the opposed triangular faces of their pyramidal bases, resting one upon another.

1. _Zygacantha lanceolata_, Haeckel.

_Acanthometra lanceolata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 48, Taf. xi. fig. 12.

_Acanthometra lanceolata_, Haeckel, 1862, Monogr. d. Radiol., p. 380.

Spines lanceolate, from the broader middle part equally thinned towards the two ends. Apex simple. Base pyramidal, without leaf-cross. Each flat lamellar spine exhibits an elevated middle rib (like a lanceolate leaf), and is therefore compressed quadrangular.

_Dimensions._--Length of the spines 0.1 to 0.15, greatest breadth (in the width) 0.03 to 0.04.

_Habitat._--Mediterranean (Saint Tropez, French shore), J. Müller; North Atlantic (Canary Islands), Haeckel, surface.

2. _Zygacantha costata_, n. sp.

Spines compressed, two-edged, linear, of nearly equal breadth in their whole length. Apex truncate. Base pyramidal, without leaf-cross. Each flat lamellar spine exhibits an elevated middle rib, which in the distal half is cleft into two divergent rods ending in the corners of the truncated apex. (Similar to _Zygacantha dicopa_, but with broader free spines, which are not grown together in the centre.)

_Dimensions._--Length of the spines 0.1 to 0.15, breadth 0.02.

_Habitat._--Central Pacific, Stations 265 to 274, surface.

{747}3. _Zygacantha compressa_, Haeckel.

_Acanthometra compressa_, Haeckel, 1862, Monogr. d. Radiol., p. 378, Taf.
xviii. figs. 4_a_, 4_b_.

Spines in the proximal half compressed, broad lanceolate, four to six times as broad as in the thin cylindrical distal half. Apex simple or short bifid. Base pyramidal, thickened, without leaf-cross. No middle rib. Central capsule opaque, yellowish or reddish-brown.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth of the inner half 0.015 to 0.02, of the outer half 0.002 to 0.003.

_Habitat._--Mediterranean (Messina); Atlantic (Canary Islands), Station 352, surface.

4. _Zygacantha furcata_, J. Müller.

_Zygacantha furcata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 51, Taf. ix. fig. 6.

_Acanthometra furcata_, J. Müller, 1856, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 499.

_Acanthometra furcata_, Haeckel, 1862, Monogr. d. Radiol., p. 380.

Spines compressed, fork-shaped, divided by two thickened knots into three sections of nearly equal length; middle section broader than the proximal, but smaller than the distal section, which is cleft by a deep fissure into two long parallel straight branches. Base pyramidal, without leaf-cross. Central capsule purple, with yellow bodies.

_Dimensions._--Length of the spines 0.1 to 0.15, basal breadth 0.003 to 0.005, distal breadth 0.02 to 0.03.

_Habitat._--Mediterranean (Cette). J. Müller, surface.

Subgenus 2. _Zygacanthidium_, Haeckel.

_Definition._--Spines at the central base with a cross of four prominent leaves; the meeting edges of the neighbouring lamellæ so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. 721).

5. _Zygacantha dichotoma_, Haeckel.

_Zygacantha dichotoma_, Haeckel, 1862, Monogr. d. Radiol., p. 381.

_Acanthometra dichotoma_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 50, Taf. ix. fig. 5.

Spines compressed, pincer-shaped, cleft nearly throughout their whole length into two thin parallel straight rods or fork branches, which are united only in their middle by a narrow bridge, and at their central base by the pyramidal small central apex; above this pyramid each rod is divided into two broad triangular leaves, forming a large basal leaf-cross. Central capsule purple, with yellow bodies.

_Dimensions._--Length of the spines 0.1 to 0.15, breadth 0.01 to 0.02.

_Habitat._--Mediterranean (Nice), J. Müller, surface.

{748}6. _Zygacantha complanata_, n. sp.

Spines compressed, two-edged, linear, of equal breadth throughout their whole length. Apex bifid. Base thickened, with a large leaf-cross. (Similar to _Amphilonche complanata_, but different in the equal size of all twenty spines, which are somewhat broader.)

_Dimensions._--Length of the spines 0.12 to 0.18, breadth 0.002.

_Habitat._--North Pacific, Station 244, surface.

7. _Zygacantha semicompressa_, Haeckel.

_Acanthometra hemicompressa_, Car, 1884, Zool. Anzeiger, p. 94, with
woodcut.

Spines in the proximal half compressed, two-edged, linear, three to four times as broad as in the needle-shaped cylindrical distal half. Apex simple. Base pyramidal, with a small leaf-cross. Central capsule transparent.

_Dimensions._--Length of the spines 0.1 to 0.2, breadth in the proximal half 0.02, in the distal half 0.006.

_Habitat._--Mediterranean (Genoa), Haeckel; Adriatic Sea (Trieste), Car, surface.

8. _Zygacantha foliacea_, n. sp.

Spines lanceolate, tapering from the broader middle part towards the two ends, with two dentated or serrated edges and a prominent middle rib. Apex simple. Base with a small leaf-cross. The spines like the leaves of _Agave americana_.

_Dimensions._--Length of the spines 0.15 to 0.2, middle breadth 0.02 to 0.03.

_Habitat._--Indian Ocean, near the Island of Socotra, Haeckel.

Subgenus 3. _Zygacanthonium_, Haeckel.

_Definition._--Spines in the centre grown perfectly together and forming a single star-shaped piece of acanthin.

9. _Zygacantha dicopa_, Haeckel.

_Astrolithium dicopum_, Haeckel, 1862, Monogr. d. Radiol., p. 400, Taf.
xx. figs. 3, 4.

Spines compressed, two-edged, linear, of nearly equal breadth throughout their whole length, with a prominent middle rib, which in the distal third is cleft into two divergent teeth, ending in the two corners of the broad, obliquely truncated apex. All twenty spines with their central bases grown together and forming one single piece of acanthin--a star with twenty rays.

_Dimensions._--Length of the spines 0.12 to 0.2, breadth 0.01 to 0.02.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, many Stations, surface.

{749}Genus 325. _Acanthonia_,[365] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with simple, four-edged, prismatic or pyramidal radial spines, without apophyses; their transverse section is square.

The genus _Acanthonia_ comprises all those Astrolonchida (formerly united with _Acanthometron_) in which the simple spines either in their whole length or in the greatest part of it are four-edged, with square transverse section. They are sometimes more prismatic (with equal breadth), at other times more pyramidal (with decreasing breadth towards the distal apex). If _Acanthometron_ be the common simple ancestral form of the Acanthonida, then the two-edged _Zygacantha_, and the four-edged _Acanthonia_ may be regarded as two divergent main lines arising from it; the former leading to the Phractacanthida and Diporaspida, the latter leading to the Stauracanthida and Tessaraspida.

Subgenus 1. _Acanthonarium_, Haeckel.

_Definition._--Spines at the central base, without leaf-cross and without hollow pyramidal compartments, united by the triangular faces of their pyramidal bases, resting one upon another.

1. _Acanthonia tetracopa_, Haeckel (Pl. 129, figs. 9-11).

_Acanthometra tetracopa_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 47, Taf. vii. figs. 3 to 5, Taf. xi. fig. 5.

_Acanthometra tetracopa_, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf.
xviii. fig. 5.

Spines quadrangular prismatic, with prominent lamellar edges, of equal breadth in their whole length. Base pyramidal, without leaf-cross. Apex truncated, or with four short teeth (sometimes only two teeth). Central capsule opaque, brown or yellow.

_Dimensions._--Length of the spines 0.15 to 0.2, breadth 0.01 to 0.012.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, many Stations, surface.

2. _Acanthonia prismatica_, n. sp.

Spines quadrangular prismatic, without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Base pyramidal, without leaf-cross. Apex truncate, with square apical face.

_Dimensions._--Length of the spines 0.1 to 0.16, breadth 0.005 to 0.008.

_Habitat._--Antarctic Ocean, Station 154, surface.

{750}3. _Acanthonia denticulata_, n. sp.

Spines quadrangular prismatic, with prominent elegantly denticulated edges, of equal breadth throughout their whole length. Both ends pyramidal, without leaf-cross. (Similar to _Amphilonche denticulata_, but with the twenty spines all equal, and with spherical central capsule.)

_Dimensions._--Length of the spines 0.12 to 0.16, breadth 0.008.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

4. _Acanthonia mülleri_, Haeckel.

_Acanthometra mülleri_, Haeckel, 1862, Monogr. d. Radiol., p. 379, Taf.
xv. fig. 3, Taf. xviii. fig. 6.

Spines quadrangular, nearly prismatic, but tapering gradually from the pyramidal base towards the distal bifid apex, which bears two thin, parallel, or little divergent teeth; four edges elegantly denticulated; base without leaf-cross. Central capsule yellowish or reddish.

_Dimensions._--Length of the spines 0.12 to 0.18, basal breadth 0.005.

_Habitat._--Mediterranean (Messina); Atlantic, Stations 348 to 352, surface.

5. _Acanthonia fragilis_, Haeckel.

_Acanthometra fragilis_, Haeckel, 1862, Monogr. d. Radiol., p. 380, Taf.
xv. fig. 4, Taf. xviii. fig. 7.

Spines quadrangular, nearly prismatic, but gradually thickened from the pyramidal base towards the distal truncated end; four edges regularly denticulated; base without leaf-cross. Central capsule opaque.

_Dimensions._--Length of the spines 0.5 and more, basal breadth 0.002 to 0.003, distal breadth 0.008 to 0.016 or more.

_Habitat._--Mediterranean (Messina); North Atlantic, Station 354, surface.

6. _Acanthonia convexa_, n. sp.

Spines quadrangular, with four broad lamellar, convex, prominent edges, which from the broader middle part are thinned towards the two emarginated ends; each end with a small quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the caudal or posterior (geotomical) spine of _Amphilonche anomala_ (Monogr. d. Radiol., Taf. xviii. fig. 23, _b_).

_Dimensions._--Length of the spines 0.12 to 0.16, breadth in the middle part 0.02 to 0.025.

_Habitat._--North Pacific, Station 244, surface.

7. _Acanthonia concava_, n. sp.

Spines quadrangular, with four broad lamellar, concave, prominent edges, which from the smaller middle part are broadened towards the two emarginated ends; each end with a small {751}quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the frontal or anterior (hydrotomical) spine of _Amphilonche anomala_ (Monogr. d. Radiol., Taf. xviii. fig. 23, _a_).

_Dimensions._--Length of the spines 0.15, breadth in the middle part 0.012, on both ends 0.025.

_Habitat._--South Pacific, Station 288, surface.

8. _Acanthonia quadrangula_, n. sp.

Spines quadrangular prismatic, with smooth prominent straight edges, but of very different breadth in both halves; the inner or proximal half (inside the central capsule) twice to four times as broad as the outer or distal half (outside the central capsule); both ends suddenly separated by a constriction, in which is inserted the membrane of the capsule. The latter is pellucid, with a number of yellow bodies. Apex of the spines simple, base pyramidal, without leaf-cross.

_Dimensions._--Length of the spines 0.2 to 0.4, breadth of the basal half 0.01, of the distal half 0.002 to 0.004.

_Habitat._--Atlantic, Canary Islands, Azores, Station 354, surface.

Subgenus 2. _Acanthonidium_, Haeckel.

_Definition._--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of these crossed lamellæ between every three or four neighbouring spines so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. 721).

9. _Acanthonia echinoides_, Haeckel.

_Acanthometra echinoides_, Claparède et Lachmann, 1858, Études sur les
Infusoires et les Rhizopodes, &c., p. 459, pl. xxiii. figs. 1-5.

_Acanthometra echinoides_, Haeckel, 1862, Monogr. d. Radiol., p. 383.

Spines quadrangular prismatic without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Central base three to four times as broad, with large leaf-cross. Apex truncated or bifid (sometimes with four short teeth).

_Dimensions._--Length of the spines 0.3 to 0.5, breadth 0.004 to 0.008; leaf-cross 0.02 to 0.03.

_Habitat._--North Atlantic, west coast of Norway (Claparède et Lachmann); Færöe Channel (Gulf Stream), John Murray, surface.

10. _Acanthonia claparedei_, Haeckel.

_Acanthometra claparedei_, Haeckel, 1862, Monogr. d. Radiol., p. 383,
Taf. xviii. fig. 12.

Spines quadrangular prismatic, with four prominent lamellar edges, of equal breadth throughout their whole length. Apex bifid. Central base twice as broad, with large leaf-cross. Central capsule opaque, reddish-brown.

_Dimensions._--Length of the spines 0.6, breadth 0.016; leaf-cross 0.032.

_Habitat._--Mediterranean (Messina); Atlantic, Station 347, surface.

{752}11. _Acanthonia cuspidata_, Haeckel.

_Acanthometra cuspidata_, Haeckel, 1862, Monogr. d. Radiol., p. 383, Taf.
xviii. fig. 11.

Spines quadrangular pyramidal, with four prominent lamellar edges, tapering gradually from the broad base towards the simple distal apex. Basal leaf-cross as broad, with a small central pyramid.

_Dimensions._--Length of the spines 0.5, basal breadth 0.012; leaf-cross 0.025.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

12. _Acanthonia quadrifolia_, Haeckel.

_Acanthometra quadrifolia_, Haeckel, 1862, Monogr. d. Radiol., p. 382,
Taf. xviii. fig. 10.

Spines in the basal part quadrangular pyramidal, with four prominent lamellar edges and a large basal leaf-cross; in the distal part three to six times as long, cylindrical, of equal breadth. Apex simple, conical, or bifid. Central capsule yellow or whitish. This common species differs from the nearly allied _Acanthometron catervatum_ mainly by the strong development of the large basal leaves or wings.

_Dimensions._--Length of the spines 0.3 to 0.5, breadth in the distal half 0.002, in the basal part 0.02.

_Habitat._--Mediterranean; North Atlantic, Stations 252 to 254; Færöe Channel, Gulf Stream, in enormous numbers, John Murray, surface and at various depths.

13. _Acanthonia diplopyramis_, n. sp.

Spines formed like a quadrangular double pyramid or an irregular octahedron; the basal leaf-cross being extremely developed, with four very large and thin lamellar leaves; the basal halves of the twenty double pyramids are united by the meeting edges of those leaves, while their distal halves are free, with simple apices. Therefore the four triangular leaves of each spine are equally thinned from the middle towards the two ends.

_Dimensions._--Length of the spines 0.1 to 0.2, greatest breadth 0.04 to 0.08.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

14. _Acanthonia multispina_, Haeckel.

_Acanthometra multispina_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 47, Taf. vii. figs. 6-9.

_Acanthometra multispina_, Haeckel, 1862, Monogr. d. Radiol., p. 384.

Spines quadrangular, with four lamellar prominent edges, in the proximal half nearly prismatic, in the distal half pyramidal; both halves separated by a prominent short tooth on each edge. Here in the middle part the breadth (including the four teeth) is equal to the basal leaf-cross. Central capsule opaque, brown.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.01 to 0.02.

_Habitat._--Mediterranean (Messina); Tropical Atlantic, Station 348.

{753}15. _Acanthonia serrulata_, n. sp.

Spines quadrangular pyramidal, with simple apex; the large basal leaf-cross nearly half as long as the prolonged distal part. The four prominent triangular edges of the latter are very thin and broad lamellæ, finely dentate or serrate.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.05 to 0.06.

_Habitat._--Central Pacific, Station 272, surface.

Subgenus 3. _Acantholithium_, Haeckel.

_Definition._--Spines in the basal part grown together, so that the whole skeleton is not composed of twenty separated pieces, but represents a single piece of acanthin--a star with twenty equal rays.

16. _Acanthonia stellata_, n. sp.

Spines quadrangular pyramidal, with simple distal apex, in the basal part grown perfectly together, so that the whole skeleton forms a single piece of acanthin--a starlet with twenty equal rays. The free pyramidal part of each spine is twice to four times as long as the basal part.

_Dimensions._--Length of the spines 0.1 to 0.15, greatest breadth (on the surface of the central solid sphere) 0.02 to 0.04.

_Habitat._--Central Pacific, Station 271, surface.

Subfamily 2. PHRACTACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with twenty radial spines, each of which bears two opposite apophyses or lateral transverse processes; sometimes two longitudinal rows of opposite apophyses.

Genus 326. _Lithophyllium_,[366] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52.

_Definition._--#Astrolonchida# with two simple, not branched, opposite apophyses on each radial spine.

The genus _Lithophyllium_ was founded by J. Müller for a single species (_Lithophyllium foliosum_), which we also here retain as the type of the genus. It is the first observed Astrolonchid, which bears two opposite lateral apophyses on each spine, and may therefore be regarded as the ancestral form of the subfamily Phractacanthida. The two opposite apophyses are here simple, whilst in the other genera of the subfamily they are branched or multiplied.

{754}1. _Lithophyllium cruciatum_, Haeckel.

_Acanthometra cruciata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 49, Taf xi. fig. 11.

_Xiphacantha cruciata_, Haeckel, 1862, Monogr. d. Radiol., p. 385, Taf.
xviii. fig. 13.

Spines cylindrical, very thin, crossed perpendicularly in the distal third by a thin transverse beam; both lateral rods of the cross have the same length as the distal end. Apex simple. Base pyramidal, without leaf-cross.

_Dimensions._--Length of the spines 0.05 to 0.15, breadth 0.001 to 0.002.

_Habitat._--Mediterranean, Atlantic, Stations 352 to 354, &c., surface.

2. _Lithophyllium gladiatum_, n. sp. (Pl. 130, fig. 3).

Spines compressed, sword-shaped, two-edged, crossed perpendicularly in the middle part by a broad, somewhat curved transverse beam; both lateral rods of the cross are triangular compressed, and have the same length as the proximal end. Apex simple. Base pyramidal, without leaf-cross.

_Dimensions_.--Length of the spines 0.2 to 0.25, breadth 0.01.

_Habitat_.--North Pacific, Station 241, surface.

3. _Lithophyllium condylatum_, n. sp.

Spines compressed quadrangular, tapering from the broader middle towards the two ends; from the middle part arise two opposite perpendicular apophyses, which bear on the rounded end a thickened condyle. Apex simple. Base pyramidal, with a small leaf-cross.

_Dimensions._--Length of the spines 0.1 to 0.12, breadth in the middle part 0.02.

_Habitat._--Central Pacific, Station 266 to 272, surface.

4. _Lithophyllium foliosum_, J. Müller.

_Lithophyllium foliosum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 52, Taf. xi. figs. 6-10.

_Xiphacantha foliosa_, Haeckel, 1862, Monogr. d. Radiol., p. 385.

Spines lanceolate, tapering from the broader middle towards the two ends. From the middle part or from the outer third arise two opposite triangular apophyses, which are not perpendicular to the axis of the spine, but form an acute angle with its distal part. Therefore each spine represents a broad leaf with a middle rib and with three lobes or truncated teeth. The distal apex is distinguished by a violet colour. Base pyramidal, without leaf-cross. Central capsule yellow.

_Dimensions._--Length of the spines 0.05 to 0.1, breadth 0.02 to 0.03.

_Habitat._--Mediterranean, French shore, Saint Tropez, J. Müller.

{755}Genus 327. _Phractacantha_,[367] Haeckel, 1881, Prodromus, p. 465.

_Definition_.--#Astrolonchida# with two branched, but not latticed, opposite apophyses on each radial spine.

The genus _Phractacantha_ differs from its ancestral form, the preceding _Lithophyllium_ by the ramification of the apophyses, which are either forked or bear lateral branches. If the prolonged fork-branches of the neighbouring spines meet and form a lattice-shell, this genus passes over into _Phractaspis_, the common ancestral form of the Diporaspida.

1. _Phractacantha_ bifurca, n. sp.

Spines cylindrical, thin, of equal breadth throughout their whole length. Apex simple. Base pyramidal, without leaf-cross. From the outer third arise two opposite, thin, forked apophyses; ends of the fork branches acute.

_Dimensions._--Length of the spines 0.1, breadth 0.006.

_Habitat._--Central Pacific, Station 274, surface.

2. _Phractacantha bipennis_, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle arise two opposite broad, forked apophyses; ends of the fork-branches broad and obtuse.

_Dimensions._--Length of the spines 0.15, breadth in the middle 0.012.

_Habitat._--Central Pacific, Station 266, surface.

Genus 328. _Doracantha_,[368] Haeckel, 1881, Prodromus, p. 465.

_Definition_.--#Astrolonchida# with two latticed or fenestrated apophyses on each radial spine.

The genus _Doracantha_ arises from the foregoing _Phractacantha_ by union of the fork-branches of the apophyses on each spine. By this concrescence is formed a polygonal or roundish plate with two pores, pierced by the radial spine between them. _Doracantha_ may be regarded as a _Dorataspis_, in which the twenty small fenestrated plates have not become united.

{756}1. _Doracantha dorataspis_, n. sp.

Spines compressed, two-edged, tapering from the broader middle towards the two ends. Apex simple. Base pyramidal, without leaf-cross. From the middle part of each spine arise two opposite forked apophyses; the neighbouring fork-branches are recurved and united in the tangential plane; so that each spine bears a plate or shield with two elliptical pores; the margin of the roundish plate bears a variable number of short teeth.

_Dimensions._--Length of the spines 0.2, breadth 0.02.

_Habitat._--Central Pacific, Station 271, surface.

Genus 329. _Astrolonche_,[369] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with numerous simple apophyses (four to eight or more on each radial spine), which are arranged in two opposite longitudinal rows (rarely in six such rows, opposite in three parallel planes).

The genus _Astrolonche_ differs from the preceding Phractacanthida in the multiplication of the simple apophyses. Commonly these are opposite in pairs in two longitudinal rows (on the two edges of the compressed spine, at least two on each side). But sometimes (in the subgenus _Astrolonchidium_) there are six instead of two longitudinal rows of teeth, and these are placed in three parallel planes.

Subgenus 1. _Astroloncharium_, Haeckel.

_Definition._--Each spine with two longitudinal rows of apophyses, opposite in one meridian plane.

1. _Astrolonche bicruciata_, n. sp.

Spines compressed, two-edged, almost of equal breadth throughout their whole length, with simple apex and small leaf-cross at the base. From the two edges of the middle part of each spine arise two pairs of opposite apophyses, which are compressed and a little curved (convex on the distal, concave on the proximal margin). All four apophyses are of the same size and form; the radial distance of each pair much smaller than their common distance from the centre.

_Dimensions._--Length of the spines 0.25, breadth 0.02.

_Habitat._--Central Pacific, Station 270, surface.

2. _Astrolonche mucronata_, Haeckel.

_Acanthometra mucronata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 49, Taf. x. fig. 9.

_Aspidomma mucronatum_, Haeckel, 1862, Monogr. d. Radiol., p. 424.

Spines conical, little compressed, with simple apex and small leaf-cross at the base. From the basal half of each spine arise two pairs of opposite apophyses, which exhibit a very different form. {757}The upper or distal apophyses (nearly in the middle of the spine) are flat, leaf-shaped, broadened in the periphery, often lobed, and sometimes branched or even fenestrated. (Transition to _Phractaspis_ and _Dorataspis_, or to _Phractopelta_?) The lower or proximal apophyses are thick, simple, all slightly curved; they are equidistant from the former and from the centre.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth 0.01.

_Habitat._--Mediterranean (Cette on the French shore), surface, J. Müller.

3. _Astrolonche pectinata_, Haeckel.

_Acanthometra pectinata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 48, Taf. x. figs. 1, 2.

_Xiphacantha pectinata_, Haeckel, 1862, Monogr. d. Radiol., p. 386.

Spines compressed quadrangular, with short, simple or bifid apex, pyramidal on the base, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; three to four slender teeth in each row.

_Dimensions._--Length of the spines 0.2, breadth 0.08.

_Habitat._--Mediterranean, Cette (French shore), surface, J. Müller.

4. _Astrolonche pinnata_, n. sp.

Spines in the distal half compressed, linear, two-edged, with bifid apex; in the proximal half three times as broad lanceolate, at the base pyramidal, without leaf-cross. From the two broader edges of the proximal half arise two longitudinal rows of opposite apophyses; four to six broad triangular teeth in each row.

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the outer half 0.012, in the inner half 0.03 to 0.04.

_Habitat._--South Atlantic, Station 332, surface.

Subgenus 2. _Astrolonchidium_, Haeckel.

_Definition._--Each spine with three parallel double rows of opposite apophyses.

5. _Astrolonche serrata_, Haeckel.

_Xiphacantha serrata_, Haeckel, 1862, Monogr. d. Radiol., p. 386, Taf.
xvii. fig. 3, Taf. xviii. figs. 14_a_, 14_b_.

_Xiphacantha serrata_, R. Hertwig, 1879, Organismus d. Radiol., p. 11,
Taf. ii. fig. 4.

_Acanthometra serrata_, Haeckel, 1860, Monogr. d. Radiol., p. 807.

Spines in the distal half thin, nearly cylindrical or a little compressed, thinned towards the short simple or bifid apex; in the proximal half three to six times as broad, four-winged, with six longitudinal rows of opposite apophyses. From the edges of the two broader (lateral) wings arise three {758}to four pairs of strong conical teeth; from the edges of the two smaller (sagittal) wings arise also three to four pairs of teeth, but very short and broad, triangular; each of these teeth bears on both its (lateral) sides two opposite slender conical teeth, which are parallel to the large conical teeth of the lateral wings. Therefore all teeth (eighteen to twenty-four) are placed opposite in pairs in three parallel planes. Base of the spines pyramidal, with a small leaf-cross. The central capsule of this large and very remarkable species commonly entirely includes the apophyses of the spines, and is opaque, whitish.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth of the distal half 0.002 to 0.004, of the proximal half 0.01 to 0.02.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface.

Subfamily 3. STAURACANTHIDA, Haeckel.

_Definition._--#Astrolonchida# with a cross of four free apophyses (or four crossed longitudinal rows of apophyses) on each radial spine.

Genus 330. _Xiphacantha_,[370] Haeckel, 1862, Monogr. d. Radiol., p. 384.

_Definition._--#Astrolonchida# with four simple apophyses on each radial spine, opposite in pairs in the form of a cross.

The genus _Xiphacantha_ was founded by me in 1862 for all those _Acanthometrida_ which bear simple or branched apophyses on their twenty equal spines. I restrict here the genus to those Astrolonchida which bear on each spine a cross of four simple, not branched, apophyses. These are either conical teeth or broad wings, sometimes extremely thin leaves. _Xiphacantha_ may be regarded as the ancestral form not only of the subfamily Stauracanthida, but also of the Tessaraspida, derived from the latter.

Subgenus 1. _Xiphacanthonia_, Haeckel.

_Definition._--Apophyses of the radial spines small, formed like a tooth or a hook, not wing-shaped. Edges of the spines commonly narrow, little prominent.

1. _Xiphacantha quadridentata_, Haeckel.

_Xiphacantha quadridentata_, Haeckel, 1862, Monogr. d. Radiol., p. 387,
Taf. xviii. figs. 15_a_, 15_b_.

_Acanthometra quadridentata_, J. Müller, 1858, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 48, Taf. x. fig. 3.

Spines slender, four-sided prismatic, gradually thinner towards the simple pyramidal apex. Base with large wing-cross. Four apophyses about in the middle of each spine, conical, straight, smooth, about as long as the basal breadth of the spine. Central capsule opaque, reddish-brown.

{759}_Dimensions._--Length of the spines 0.2 to 0.3, breadth in the middle part 0.012, on the base 0.02; length of the apophyses 0.02 to 0.03.

_Habitat._--Mediterranean, Atlantic, Stations 348, 354, surface.

2. _Xiphacantha crucifera_, n. sp.

Spines slender, four-sided prismatic, thin, of nearly equal breadth throughout the whole length. Base with small wing-cross. Four apophyses much nearer the proximal than the distal end, thin, straight smooth, three to six times as long as the basal breadth of the spine. Central capsule pellucid, with yellow bodies.

_Dimensions._--Length of the spines 0.4 to 0.5, breadth 0.002 to 0.004; length of the apophyses 0.01 to 0.02.

_Habitat._--Central Pacific, Station 266, surface.

3. _Xiphacantha spinulosa_, Haeckel.

_Xiphacantha spinulosa_, Haeckel, 1862, Monogr. d. Radiol., p. 388, Taf.
xvii. fig. 4.

_Acanthometra spinulosa_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 807.

Spines stout, four-sided prismatic, of nearly equal breadth throughout the whole length, on the distal apex truncated, two-edged. Base with large wing-cross. Four apophyses about in the middle of each spine, conical, straight, spinulated, twice to four times as long as the basal breadth of the spine. Central capsule opaque, yellow.

_Dimensions._--Length of the spines 0.27, breadth 0.014; length of the apophyses 0.05.

_Habitat._--Mediterranean (Messina), surface.

4. _Xiphacantha emarginata_, n. sp.

Spines stout, four-sided, in the proximal half prismatic, in the distal half pyramidal, with emarginated apex. Base with very large wing-cross. Four apophyses about in the middle of each spine, compressed, straight, two-edged, with emarginated ends, about twice as long as the basal breadth of the spine. Central capsule small, pellucid.

_Dimensions._--Length of the spines 0.2 to 0.3, breadth 0.02 to 0.03; length of the apophyses 0.04 to 0.06.

_Habitat._--South Pacific, Station 291, surface.

5. _Xiphacantha falcata_, n. sp.

Spines slender, four-sided prismatic, gradually thickened from both ends towards the middle part, with simple apex. Base with very small wing-cross. Four apophyses about in the middle part of each spine, falcated, compressed, recurved, twice to three times as long as the greatest breadth of the spine.

{760}_Dimensions._--Length of the spines 0.3 to 0.4, greatest breadth 0.015; length of the apophyses 0.03 to 0.05.

_Habitat._--Central Pacific, Station 270, surface.

6. _Xiphacantha ancorata_, n. sp.

Spines slender, four-sided prismatic, gradually thickened from the narrow base towards the short, simple, pyramidal apex. Base with large wing-cross. Four apophyses on the distal end, immediately below the pyramidal apex, falcated, strongly recurved, like an anchor with four strong teeth.

_Dimensions._--Length of the spines 0.4 to 0.5, basal breadth 0.005, distal breadth 0.015; length of the apophyses 0.04.

_Habitat._--Indian Ocean, Madagascar, Rabbe.

Subgenus 2. _Xiphacanthidium_, Haeckel.

_Definition._--Apophyses of the radial spines broad, compressed, wing-shaped, formed like a large thin plate. Edges of the spines commonly broad, strongly prominent.

7. _Xiphacantha stauroptera_, n. sp.

Spines four-winged, from the middle part little thinner towards both ends. Apex simple pyramidal. Base with small wing-cross. Four apophyses wing-shaped, isosceles triangular or truncated quadrangular; their base is about half as broad as their length, and occupies in the basal half of each spine about one-sixth to one-eighth of its length.

_Dimensions._--Length of the spines 0.1 to 0.15; greatest breadth (diagonal of the cross of the apophyses) 0.006 to 0.009.

_Habitat._--South Atlantic, Station 332, surface.

8. _Xiphacantha trigonoptera_, n. sp.

Spines four-winged, tapering rapidly from the broad middle part towards both ends. Apex simple pyramidal. Base with a small wing-cross. Four apophyses equilateral triangular; their base occupies the middle of each spine, extending to about one-fifth of its length.

_Dimensions._--Length of the spines 0.15 to 0.2, greatest breadth (diagonal of the cross of the apophyses) 0.06 to 0.08.

_Habitat._--Central Pacific, Station 272, surface.

9. _Xiphacantha macroptera_, n. sp.

Spines four-winged, from the broad middle part gradually thinner towards both ends. Apex simple pyramidal. Base with small wing-cross. Four apophyses wing-shaped, very long and broad, {761}triangular; their base occupies about the middle third of each spine; the proximal side of each wing is the shortest, truncated or concave.

_Dimensions._--Length of the spines 0.4 to 0.5, greatest breadth (diagonal of the middle leaf-cross) 0.08 to 0.12.

_Habitat._--North Pacific, Stations 253 to 256, surface.

10. _Xiphacantha platyptera_, n. sp.

Spines four-winged, nearly prismatic in the basal and distal parts. Apex truncated. Base with small wing-cross. Four apophyses wing-shaped, very broad and thin, extremely delicate, of irregular quadrangular or nearly rhomboidal form; their base occupies the middle half of the length of the spines (second and third quarter). Very variable in form. Often the edges of the wing-apophyses of the neighbouring spines seem to meet.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth (diagonal of the leaf-cross) 0.06 to 0.08.

_Habitat._--Pacific, widely distributed, Stations 239, 253, 272, 288, &c., surface.

11. _Xiphacantha ciliata_, n. sp. (Pl. 129, figs. 4, 5).

Spines four-winged, prismatic in the basal and the distal third. Apex pyramidal, short. Base with large leaf-cross. Four apophyses wing-shaped, nearly semicircular, with dentated edges and rough spinulate or porous faces; their base occupies the middle third of the length of each spine.

_Dimensions._--Length of the spines 0.2 to 0.3, greatest breadth (diagonal of the apophysial cross) 0.08 to 0.12.

_Habitat._--Tropical Atlantic, Stations 342 to 352, surface.

12. _Xiphacantha alata_, Haeckel.

_Xiphacantha alata_, Haeckel, 1862, Monogr. d. Radiol., p. 388.

_Acanthometra alata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 48, Taf. ix. figs. 1-3.

Spines four-winged, prismatic in the basal quarter, more slender in the distal half. Apex simple pyramidal. Base with small wing-cross. Four apophyses wing-shaped, nearly semicircular, with denticulated edges (and often also with spinulate faces); their base occupies the second quarter of the length of each spine.

_Dimensions._--Length of the spines 0.3 to 0.4, greatest breadth (diagonal of the apophysial cross) 0.05 to 0.06.

_Habitat._--Mediterranean (Nice), Müller, (Portofino), Haeckel.

Genus 331. _Stauracantha_,[371] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with four branched (but not latticed) apophyses on each radial spine, opposite in pairs in the form of a cross.

{762}The genus _Stauracantha_ differs from its ancestral form, _Xiphacantha_, in the ramification of the four crossed apophyses on each spine. These bear either lateral branches, which are parallel to the cross axes of the radial spine itself (subgenus _Stauracanthonium_), or they are forked, with divergent branches not parallel to those cross axes (subgenus _Stauracanthidium_). Both subgenera may perhaps be better separated as genera. They form the transition to the _Stauraspida_.

Subgenus 1. _Stauracanthonium_, Haeckel.

_Definition._--Apophyses of the radial spines not forked, but crossed by perpendicular branches, which are placed in tangential planes and parallel to the cross axes of the quadrangular spine itself.

1. _Stauracantha orthostaura_, n. sp. (Pl. 130, fig. 5).

Spines four-sided prismatic, with simple apex and small leaf-cross at the base; with four thin slender conical apophyses in the proximal third. Each apophysis represents a regular rectangular cross, being intersected in its middle by one perpendicular rod of its own length.

_Dimensions._--Length of the spines 0.3, breadth 0.02; distance of the apophyses from the apex 0.15 to 0.2.

_Habitat._--South Pacific, Station 169, surface.

2. _Stauracantha tetrastaura_, n. sp.

Spine four-winged prismatic, with four broad prominent edges, pyramidal apex, and large basal leaf-cross, with four broad compressed apophyses about in the middle. Each apophysis represents a vertical lamella (placed in a meridian) with convex distal and concave proximal edge, and is crossed in its apical part by one perpendicular short rod.

_Dimensions._--Length of the spines 0.5, breadth 0.03; distance of the apophyses from the centre 0.2.

_Habitat._--Central Pacific, Station 272, surface.

3. _Stauracantha diplostaura_, n. sp.

Spines four-sided prismatic, with truncated apex and broad basal leaf-cross; in the proximal half with four slender conical apophyses. Each apophysis is crossed in its apical half at right angles by two short parallel transverse rods.

_Dimensions._--Length of the spines 0.32, breadth 0.012; distance of the apophyses from the centre 0.11.

_Habitat._--South Pacific, Station 291, surface.

{763}4. _Stauracantha scalaris_, n. sp.

Spines four-winged prismatic, with four broad prominent edges, truncated apex, and small basal leaf-cross; in the proximal third with four compressed lamellar apophyses. Each apophysis is pinnate with opposite pinnulæ, or crossed at right angles by three to six parallel transverse rods.

_Dimensions._--Length of the spines 0.24, breadth 0.016; central distance of the apophyses 0.12.

_Habitat._--Indian Ocean (Madagascar), Rabbe, surface.

5. _Stauracantha johannis_, n. sp. (Pl. 132, fig. 11).

Spines four-sided pyramidal, with simple apex and broad basal leaf-cross, with four large conical apophyses about in their middle. Each apophysis bears two irregular rows of alternating perpendicular lateral branches, the length of which decreases from the base towards the apex of the apophysis.

_Dimensions._--Length of the spines 0.2, middle breadth 0.02; central distance of the apophyses 0.1.

_Habitat._--South-east Pacific (off Juan Fernandez), Station 300, surface.

6. _Stauracantha murrayana_, Haeckel.

_Xiphacantha species_, Wyville Thomson, 1877, The Atlantic, vol. i. p.
235, fig. 53.

_Xiphacantha murrayana_, Haeckel, 1878, Protistenreich, p. 45, fig. 33.

Spines quadrangular prismatic, with pyramidal apex and small basal leaf-cross, with four regular conical apophyses in the proximal part. Each apophysis is crossed at right angles by two parallel transverse rods; the smaller apical rod is simple; the larger basal rod is crossed again on each side by a secondary perpendicular branch, which therefore is parallel to the apophysis itself.

_Dimensions._--Length of the spines 0.3, breadth 0.01, distance of the apophyses 0.08.

_Habitat._--South Atlantic, Station 332, surface.

7. _Stauracantha pinnulata_, n. sp.