Chapter XI: Literature and History (34)

Spines four-winged pyramidal, with prominent edges, simple apex and large basal leaf-cross, in the middle with doubly pinnate triangular apophyses. Each apophysis is crossed at right angles by three to four transverse parallel rods, which bear again perpendicular secondary branches; the outline of the doubly pinnate apophysis is an isosceles triangle.

_Dimensions._--Length of the spines 0.3, middle breadth 0.02; distance of the apophyses 0.12.

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

{764}Subgenus 2. _Stauracanthidium_, Haeckel.

_Definition._--Apophyses of the radial spines forked, each with two divergent terminal branches, which are not parallel to the cross axes of the quadrangular spine.

8. _Stauracantha stauraspis_, Haeckel.

_Dorataspis polyancistra, juvenis_, Haeckel, 1862, Monogr. d. Radiol., p.
418, Taf. xxi. fig. 7.

Spines slender, quadrangular prismatic, with simple apex and pyramidal base (without basal leaf-cross); with four slender apophyses, which are simply forked in the outer third. Each apophysis with two recurved fork branches.

_Dimensions._--Length of the spines 0.12, breadth 0.004; distance of the apophyses 0.06.

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

9. _Stauracantha bifurca_, n. sp.

Spines stout, four-winged prismatic, with pyramidal apex and pyramidal base (without leaf-cross); in their middle with four compressed, little curved apophyses (convex on the outer, concave on the inner edge), which are simply forked at the end. Each apophysis with two short straight fork branches.

_Dimensions._--Length of the spines 0.2, breadth 0.006; distance of the apophyses 0.08.

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

10. _Stauracantha quadrifurca_, n. sp. (Pl. 130, fig. 4).

Spines slender, four-sided prismatic, with simple apex and pyramidal base (without leaf-cross); with four slender apophyses, which are doubly forked about in their middle. Each apophysis with four short and thin terminal branches.

_Dimensions._--Length of the spines 0.2, breadth 0.002; distance of the apophyses from the centre 0.08.

_Habitat._--South Atlantic, Stations 325 to 330, surface.

Genus 332. _Phatnacantha_,[372] Haeckel, 1881, Prodromus, p. 465.

_Definition._--#Astrolonchida# with four apophyses on each radial spine, opposite in pairs in cross form, and forming a lattice-plate by communicating branches.

The genus _Phatnacantha_ has been derived from the preceding _Stauracantha_ by concrescence of the branches of the apophyses. Therefore each spine bears a lattice-plate or a fenestrated shield. If the growing plates of the neighbouring spines {765}meet together, then the characteristic lattice-shell of the Tessaraspida is perfect. Either each plate bears four crossed pores (like _Tessaraspis_), or a larger number of pores (four aspinal and four to eight or more coronal) like _Icosaspis_.

1. _Phatnacantha tessaraspis_, n. sp.

Spines quadrangular prismatic, with simple pyramidal apex and small basal leaf-cross. Each spine bears in the basal half a square plate, which is perforated by four square pores; margin of the plate with twelve short straight teeth.

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

_Habitat._--Central Pacific, Station 265, surface.

2. _Phatnacantha icosaspis_, n. sp. (Pl. 130, fig. 6).

Spines quadrangular with prominent edges; prismatic in the basal half, with a broad basal leaf-cross, pyramidal in the distal half, with a simple or truncate apex. Each spine bears in the middle part a square plate, which is perforated by eight to sixteen or more square pores (four aspinal and four to eight or more coronal); margin of the plate with twenty-four to forty-eight or more short straight irregular compressed teeth.

_Dimensions._--Length of the spines 0.18, breadth 0.008.

_Habitat._--Central Pacific, Station 273, surface.

Genus 333. _Pristacantha_,[373] n. gen.

_Definition._--#Astrolonchida# with numerous simple apophyses (eight to sixteen or more on each radial spine) which are arranged in four longitudinal rows opposite in pairs in the form of a cross.

The genus _Pristacantha_ differs from all other Stauracanthida in the multiplication of the crossed apophyses (at least eight on each spine), and exhibits therefore to them the same relation as _Astrolonche_ exhibits to the other Phractacanthida. The remarkable _Astrolonchidium serratum_ appears intermediate between both groups.

1. _Pristacantha octodon_, n. sp. (Pl. 130, fig. 9).

Spines four-sided prismatic, a little broader in the middle part than at either end, with thin prominent edges. Apex truncate or pyramidal. Base pyramidal, with a small leaf-cross. From the four edges arise in the basal half (between first and second third of the length) eight slender, conical, or triangular apophyses (two on each edge).

_Dimensions._--Length of the spines 0.4 to 0.6, breadth 0.02 to 0.04.

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

{766}2. _Pristacantha dodecodon_, n. sp. (Pl. 130, fig. 8).

Spines four-winged, of lanceolate outline, tapering from the broader middle towards the two ends. Apex pyramidal. Base with a large leaf-cross. From the four wings arise in the basal part (between first and second third of the length) twelve triangular apophyses (three from each wing).

_Dimensions._--Length of the spines 0.3, breadth in the middle 0.03.

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

3. _Pristacantha polyodon_, n. sp. (Pl. 130, fig. 7).

Spines in the distal half four-sided prismatic, thin, with pyramidal apex; in the basal half much broader, four-winged, with a large leaf-cross on the base. From the four wings of the basal half arises a variable number of slender teeth or triangular apophyses, commonly sixteen to twenty-four, often irregular (four to six from each wing).

_Dimensions._--Length of the spines 0.3 to 0.4, breadth in the distal part 0.007 to 0.01, in the basal part 0.02 to 0.03.

_Habitat._--South Pacific (off New Zealand), Station 169, surface.

Family XXXVII. #QUADRILONCHIDA#, Haeckel (Pl. 131).

_Acanthostaurida_, Haeckel, 1881, Prodromus, p. 466.

_Definition._--ACANTHARIA with twenty radial spines of very unequal size, disposed according to the law of the Icosacantha; four equatorial spines much larger than the sixteen others. No lattice-shell.

The family #Quadrilonchida# differs from the foregoing ancestral family, the Astrolonchida, in the unequal development of the twenty radial spines. The four equatorial spines are constantly much larger, and often also of another form and shape, than the sixteen other spines; often also among these the eight tropical spines are larger and of another form than the eight polar spines. Therefore the five parallel girdles or zones of every four spines, which in the Astrolonchida are equal, are here distinctly unequal. The whole body is flattened and compressed in the direction of the spineless axis, so that the equatorial plane is larger than any other plane, laid through the centre. In consequence of this flattening the central capsule is also commonly compressed and flattened, lenticular or discoidal, rarely spherical. In the Astrolonchida the "promorph" or the "geometrical fundamental form" is constantly a square double pyramid, the axes of which are of equal length. In the Quadrilonchida it becomes a square double pyramid, the two equatorial axes of which (or the diagonals of the square) are constantly longer than all other axes.

In the simpler forms of Quadrilonchida are found only two different kinds of spines, the four larger equatorial spines being of the same size and form, and the sixteen smaller {767}spines also not differing from one another (_Acanthostaurus_, &c.). But in the majority of this family there are three different kinds: four larger equatorial spines, eight tropical spines of middle size, and eight smaller polar spines (_Belonostaurus_, &c.); the latter become sometimes rudimentary, so that only twelve spines are developed (four larger equatorial and eight smaller tropical spines). In this case the development of the flat discoidal body is much stronger in the equatorial plane than in all other planes. These discoidal or lenticular Quadrilonchida exhibit a relation to the spherical Astrolonchida similar to that which the #Discoidea# exhibit to the #Sphæroidea# among the #Sphærellaria#.

A further morphological differentation takes place in the remarkable genera _Lonchostaurus_ and _Zygostaurus_. In the former (Pl. 131, figs. 4-6) the four larger equatorial spines becomes differentiated in pairs, so that the opposite equal spines of one pair, _c_1, _c_3 (in the longitudinal or hydrotomical axis), are larger, and often also of another form, than the opposite equal spines of the other pair, _c_2, _c_4 (in the transverse or geotomical axis). The most peculiar form is the rather common _Zygostaurus_ (Pl. 131, figs. 7, 8). Here the two opposite spines of one equatorial axis (of the longitudinal axis) become very different, so that the anterior or frontal spine (_c_1) is very unequal to the posterior or caudal spine (_c_3), whereas the two opposite spines, of the other equatorial axis (of the transverse axis) remain equal (_c_2, _c_4). Therefore the fundamental forms become here "amphithect," as in the Ctenophora.

The numerous Quadrilonchida may be disposed in two different subfamilies: in the Acanthostaurida all twenty radial spines are simple, without apophyses; in the Lithopterida all twenty spines (or only one part of them) bear two opposite apophyses (or lateral transverse processes). The former correspond to the Zygacanthida, the latter to the Phractacanthida among the Astrolonchida. The two opposite apophyses are simple in _Quadrilonche_ (Pl. 133, fig. 1). In _Xiphoptera_ they are provided on their distal side with lateral branches which are parallel to the spine itself. In _Lithoptera_ the spines bear two to four parallel pairs of transverse apophyses, and these are crossed by perpendicular branches, parallel to the spine itself, so that there arise fenestrated wings or latticed plates, comparable to the sails of a wind-mill. The lattice-work of these plates lies in the same meridian plane with the radial spine itself, and is therefore not comparable to the fenestrated apophyses of _Doracantha_, of _Phatnacantha_, and of the Dorataspida; in these the lattice-plates lie in tangential planes, perpendicular to the radial spine.

The apophyses of the Lithopterida may be developed either on all twenty spines equally, or only on twelve spines (four equatorial and eight tropical, whilst the eight polar spines are simple, Pl. 131, fig. 10), or only on the four equatorial spines (whilst the sixteen others are simple, Pl. 131, fig. 9).

_The Central Capsule_ of the Quadrilonchida is rarely spherical, commonly more or {768}less compressed from both poles of the spineless axis, lenticular or discoidal, sometimes square. It is enveloped by a voluminous calymma constantly bearing coronals of "Myophrisca" (compare p. 724).

_Synopsis of the Genera of Quadrilonchida._

-------------------------------------------------------------------------
I. Subfamily Acanthostaurida.
All twenty spines simple, without lateral apophyses (sometimes forked,
but neither branched nor latticed).
-------------------------------------------------------------------------
{ Eight tropical and
{ eight polar spines
{ nearly equal, 334. _Acanthostaurus_.
Four equatorial spines of {
equal size and form. { Eight tropical and
{ eight polar spines
{ very different, 335. _Belonostaurus_.

{ Two principal spines
Four equatorial spines of { of equal size and
very different size or { form, 336. _Lonchostaurus_.
form (the two lateral {
constantly equal). { Two principal spines
{ (frontal and caudal)
{ very different, 337. _Zyostaurus_.
-------------------------------------------------------------------------
II. Subfamily Lithopterida.
Either all twenty spines or a part of them provided with two opposite
lateral branches or apophyses.
-------------------------------------------------------------------------
Apophyses simple, neither branched nor latticed, 338. _Quadrilonche_.

Apophyses branched or pinnate, but not latticed, 339. _Xiphoptera_.

Apophyses latticed, with fenestrated network, 340. _Lithoptera_.

Subfamily 1. ACASTHOSTAURIDA, Haeckel, 1881, Prodromus, p. 466.

_Definition._--#Quadrilonchida# with simple radial spines, without apophyses.

Genus 334. _Acanthostaurus_,[374] Haeckel, 1862, Monogr. d. Radiol., p. 395.

_Definition._--#Quadrilonchida# with four equatorial spines of equal size and form, which are much larger than the sixteen other spines. Eight tropical and eight polar spines nearly equal. No apophyses.

The genus _Acanthostaurus_ is the most simple and primitive form of the Quadrilonchida, and the common ancestral genus of this family; it is at the same time its most common and widely distributed form. Some species appear in astonishing numbers in different seas. It has been derived from _Acanthometron_ by stronger development of the four equatorial spines, which are all of equal size and much larger than the sixteen others.

{769}Subgenus 1. _Acostaurus_, Haeckel.

_Definition._--All twenty spines separated, in the centre united only by the triangular faces or the meeting leaf-shaped edges of their pyramidal bases.

1. _Acanthostaurus aequatorialis_, n. sp.

Spines cylindrical, of nearly equal breadth throughout their whole length. Apex simple conical. Base with a large leaf-cross. Four equatorial spines of the same form as the sixteen others, but much longer and about three times as broad.

_Dimensions._--Length of the four major spines 0.2 to 0.25, breadth 0.008; length of the sixteen minor spines 0.01 to 0.15, breadth 0.003.

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

2. _Acanthostaurus bipennis_, n. sp.

Spines linear, sword-shaped, strongly compressed, two edged; of nearly equal breadth in their whole length. Apex bifid. Base with a small leaf-cross. Four equatorial spines of the same form as the sixteen others, but twice as long and as broad.

_Dimensions._--Length of the four major spines 0.4 to 0.5, of the sixteen minor 0.2 to 0.3; breadth of the former 0.02, of the latter 0.01.

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

3. _Acanthostaurus conacanthus_, n. sp.

Spines conical, short, gradually tapering from the thick base towards the simple apex. Base with large leaf-cross. Four equatorial spines more cylindrical, twice to three times as long and as broad as the sixteen others.

_Dimensions._--Length of the four major spines 0.15 to 0.2, of the sixteen minor 0.05 to 0.08; basal breadth of the former 0.03, of the latter 0.012.

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

4. _Acanthostaurus purpurascens_, Haeckel.

_Acanthostaurus purpurascens_, Haeckel, 1862, Monogr. d. Radiol., p. 395,
Taf. xix. figs. 1, 2.

_Acanthostaurus purpurascens_, R. Hertwig, 1879, Organism. d. Radiol.,
Taf. i. figs. 8, 9, Taf. iii. figs. 13, 15.

_Acanthometra purpurascens_, Haeckel, 1860, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 809.

Spines nearly cylindrical, with four blunt (often scarcely visible) edges, tapering slightly from the central to the distal end. Apex bifid, with two short parallel teeth. Base with a broad leaf-cross. {770}Four equatorial spines one and a half times to twice as long and broad as the sixteen others. Central capsule cruciate, with four arms (enveloping the basal part of the four large spines); filled up with yellow bodies and purple granules. Calymma large, with a network of purple granules. The four main spines are constantly much larger than the sixteen others, but in variable proportion. The eight polar spines are sometimes rudimentary.

_Dimensions._--Length of the four major spines 0.3 to 0.4, of the sixteen minor 0.15 to 0.3; breadth of the former 0.012, of the later 0.008 or less.

_Habitat._--Mediterranean (Messina); Atlantic, Stations 348 to 354, surface.

5. _Acanthostaurus pallidus_, Haeckel.

_Acanthostaurus pallidus_, Haeckel, 1862, Monogr. d. Radiol., p. 396.

_Acanthometra pallida_, Claparède et Lachmann, 1858, Études sur les
Infusoires, &c., p. 461, Taf. xxiv. fig. 6.

Spines four-sided prismatic, with four blunt edges, of nearly equal breadth throughout their whole length. Apex bifid. Base with a small leaf-cross. Four equatorial spines much larger than the sixteen others. Central capsule spherical, transparent, containing some yellow bodies.

_Dimensions._--Length of the four main spines 0.12 to 0.2, of the sixteen others 0.04 to 0.08; breadth of the former 0.01, of the latter 0.004.

_Habitat._--North Atlantic, west coast of Norway, Claparède; Færöe Channel, John Murray.

6. _Acanthostaurus forceps_, Haeckel.

_Acanthostaurus forceps_, Haeckel, 1862, Monogr. d. Radiol., p. 396, Taf.
xix. figs. 3, 4.

_Acanthometra forceps_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 809.

Spines pincer-shaped, linear, compressed, cleft nearly throughout their whole length into two parallel thin, straight branches, which are united only at the pyramidal base and by means of a small bridge in the middle part. Four main spines twice as long and as broad as the sixteen others. Central capsule square, filled up with red pigment, and containing yellow bodies. The diagonals of the square are the two equatorial axes.

_Dimensions._--Length of the four main spines 0.1, of the sixteen others 0.05; breadth of the former 0.01, of the latter 0.005.

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

7. _Acanthostaurus hastatus_, Haeckel.

_Acanthostaurus hastatus_, Haeckel, 1862, Monogr. d. Radiol., p. 397,
Taf. xix. fig. 5.

_Acanthometra hastata_, Haeckel, 1860, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 809.

Spines of very different size and form; four equatorial spines cylindrical in the basal half, spear-shaped or lanceolate in the distal half, with thin edges, little longer, but five to eight times as {771}broad as the sixteen smaller spines, which are cylindrical, of equal breadth throughout their whole length, with bifid apex. Base of all twenty spines pyramidal, without leaf-cross. Central capsule yellow, spherical, or lenticular.

_Dimensions._--Length of the four major spines 0.066, breadth in the middle 0.005, on the apex 0.008; length of the sixteen smaller spines 0.054, breadth 0.001.

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

Subgenus 2. _Staurolithium_, Haeckel, 1862, Monogr. d. Radiol., p. 401.

_Definition._--All twenty spines in the centre melted and grown together, forming one single, star-like piece of acanthin.

8. _Acanthostaurus cruciatus_, Haeckel.

_Staurolithium cruciatum_, Haeckel, 1862, Monogr. d. Radiol., p. 401,
Taf. xx. fig. 6.

_Astrolithium cruciatum_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 811.

Spines cylindrical, of equal breadth throughout their whole length. Apex simple conical. Four equatorial spines twice as long and broad as the sixteen other spines. All twenty spines in the centre melted and grown together, forming a single piece of acanthin. Central capsule spherical, red-brown, opaque.

_Dimensions._--Length of the four equatorial spines 0.12, breadth 0.006; length of the sixteen smaller spines 0.06, breadth 0.003.

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

Genus 335. _Belonostaurus_,[375] n. gen.

_Definition._--#Quadrilonchida# with four equatorial spines of equal size and form, which are much larger than the sixteen other spines. Eight tropical and eight polar spines very different. No apophyses.

The genus _Belonostaurus_ differs from the preceding _Acanthostaurus_ in the unequal size and form of the eight tropical and the eight polar spines; the latter are much smaller than the former and often quite rudimentary, so that the skeleton appears composed only of twelve spines, four larger equatorial and eight smaller tropical spines. The central bases of the polar spines are constantly preserved. The central capsule is a flattened square disk.

1. _Belonostaurus quadratus_, n. sp.

Four equatorial spines little compressed, almost cylindrical in the basal half, lanceolate, broader, with simple apex in the distal half. Eight tropical spines a little shorter, but only half as broad, {772}sword-shaped, two-edged, of equal breadth, with simple apex. Eight polar spines very short, conical, also with simple apex. Base without leaf-cross, a simple pyramid.

_Dimensions._--Length of the four equatorial spines 0.18, of the eight tropical spines 0.14, of the eight polar spines 0.04.

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

2. _Belonostaurus bicuspis_, n. sp.

Four equatorial spines compressed, almost lanceolate in the basal half, bifid, with two large, bent, little divergent horns in the distal half. Eight tropical spines nearly of the same form, but only half as large, with much smaller horns. Eight polar spines rudimentary, very short, conical, with simple apex. Base with a large leaf-cross.

_Dimensions._--Length of the four equatorial spines 0.2, of the eight tropical spines 0.1, of the eight polar spines 0.02.

_Habitat._--Central Pacific, Station 263, surface.

Genus 336. _Lonchostaurus_,[376] Haeckel, 1862, Monogr. d. Radiol., p. 397 (_sensu emendato_).

_Definition._--#Quadrilonchida# with four equatorial spines of unequal size and form; the principal spines (in the longitudinal axis) larger than the lateral spines (in the transverse axis); both opposite spines of each pair equal. Sixteen other spines much smaller (often the eight tropical larger than the eight rudimentary polar spines). No apophyses.

The genus _Lonchostaurus_ differs from the two preceding genera in the unequal size and shape of both equatorial pairs of spines, whilst the two opposite spines of each pair are equal. Therefore the equatorial plane is here a rhombus, not a square, as in the preceding genera. We encounter here for the first time the differentiation of the two equatorial axes, the longitudinal (or hydrotomical) and the transverse (or geotomical) axis. The sixteen other spines are constantly smaller (often also the eight polar more or less rudimentary).

1. _Lonchostaurus rhomboides_, n. sp. (Pl. 131, fig. 6).

Four equatorial spines cylindrical, twice to three times as broad as the sixteen smaller spines, conical at the distal apex; the two opposite spines of the longitudinal axis twice as long as those of the transverse axis. Sixteen smaller spines conical at the base, with simple bristle-shaped apex. The surface of the rhombical calymma, including the spines, was covered in the figured specimen with small plates like those of _Sphærocapsa_.

_Dimensions._--Length of the cross (longitudinal axis) 0.24, breadth (transverse axis) 0.12.

_Habitat._--South Pacific, Station 302, depth 1450 fathoms.

{773}2. _Lonchostaurus lanceolatus_, n. sp.

Four equatorial spines compressed, lanceolate, tapering equally from the middle towards the two ends; the two opposite spines of the longitudinal axis one and a half times as long as those of the transverse axis. Sixteen smaller spines compressed, linear, two-edged, half as long and only one-fourth as broad as the two longitudinal spines.

_Dimensions._--Length of the equatorial cross 0.3, breadth 0.2.

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

3. _Lonchostaurus bifidus_, n. sp.

Four equatorial spines compressed, nearly rectangular, forked, with two long and thin, bent, little divergent horns; the two opposite spines of the longitudinal axis about one-third longer and broader than those of the transverse axis. Sixteen smaller spines of the same form, also forked, but the eight tropical only half as large, and the eight polar spines scarcely one-fourth as large as the two longitudinal spines.

_Dimensions._--Length of the equatorial cross 0.36, breadth 0.26.

_Habitat._--South-west Pacific, Station 166, surface.

4. _Lonchostaurus bifurcus_, n. sp. (Pl. 131, fig. 4).

Four equatorial spines nearly rhomboidal, about one and a half times as large as the eight tropical and three times as large as the eight polar spines; the two opposite spines of the longitudinal axis only with two large divergent straight horns; the two spines of the transverse axis somewhat shorter, with four short horns (the two outer horns longer than the two inner). Eight tropical spines doubly forked, each with four thin bristle-shaped horns. Eight polar spines very short, each with two thin bristle-shaped, much divergent horns.

_Dimensions._--Length of the equatorial cross 0.34, breadth 0.28.

_Habitat._--North-west Pacific, Station 236, surface.

5. _Lonchostaurus rhombicus_, n. sp.

Four equatorial spines nearly rhomboidal, tapering from the broader middle towards the two ends. Leaf-cross of their base very large. The two opposite spines of the longitudinal axis about one-third larger than the two spines of the transverse axis. Eight tropical spines of the same form, but only half as large. Eight polar spines rudimentary, very short, conical.

_Dimensions._--Length of the equatorial cross 0.4, breadth 0.3.

_Habitat._--North Pacific, Station 253, surface.

6. _Lonchostaurus crystallinus_, n. sp. (Pl. 131, fig. 5).

Four equatorial spines lanceolate or rhomboidal, with broad leaf-cross at the base, of a peculiar crystalline structure and a lamellated surface, both opposite spines of the longitudinal axis twice as {774}large as the two spines of the transverse axis. Eight tropical spines of similar form, but only half as large, and with a very large, extremely prominent, lamellated leaf-cross. Eight polar spines quite rudimentary, scarcely prominent.

_Dimensions._--Length 0.36, breadth 0.2.

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

Genus 337. _Zygostaurus_,[377] n. gen.

_Definition._--#Quadrilonchida# with four equatorial spines of unequal size and form; both lateral spines (in the transverse axis) equal; but both principal spines (in the longitudinal axis) very different, the frontal larger than the caudal. Sixteen other spines much smaller (often the eight tropical larger than the eight rudimentary polar spines). No apophyses.

The genus _Zygostaurus_ differs from all other Staurolonchida in the peculiar differentiation of the four equatorial spines; the two opposite spines of the hydrotomical or longitudinal axis being very different in size and form (the frontal spine forked, the caudal spine simple); whilst the two opposite spines of the geotomical or lateral axis (perpendicular to the former) are equal, forked, but different in shape from the former. Therefore the geometrical fundamental form of the body in this remarkable genus becomes "amphithect" or "bilateral" in the widest signification of this term (comp. my General Morphology, vol. i. pp. 480, 482). Of the three different dimensive axes one (the longitudinal) exhibits unequal poles, whilst the two other (the sagittal and lateral) axes exhibit equal poles.

1. _Zygostaurus amphithectus_, n. sp. (Pl. 131, fig. 7).

Frontal spine (_c_1) little different from the two lateral spines; each with two divergent curved horns, which are equal and of about the same length as the simple broad basal part. Caudal spine (_c_3) simple, spindle-shaped, about as long as the frontal spine. Tropical spines little smaller than the three former, and of the same symmetrical forked form. Eight polar spines much smaller, but also forked, with thin bristle-shaped branches.

_Dimensions._--Length of the cross (longitudinal axis) 0.5, breadth (lateral axis) 0.4.

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

2. _Zygostaurus longicornis_, n. sp.

Frontal spine (_c_1) little different from the two lateral spines, each with two divergent curved horns, which are equal and of about the same length as the simple broad basal part. Caudal {775}spine (_c_3) simple, lanceolate, shorter than the frontal spine. Eight tropical spines in the basal part smaller than the three former, but with much longer fork-branches, which are prolonged into very thin and long bristles. Eight polar spines rudimentary, very short.

_Dimensions._--Length of the equatorial cross 0.4, breadth 0.3.

_Habitat._--South Pacific, Station 295, surface.

3. _Zygostaurus cornutus_, n. sp.

Frontal spine (_c_1) little different from the two lateral spines, each with two divergent straight horns, which are shorter than the basal part. Caudal spine (_c_3) simple, triangular, shorter than the three former. Eight tropical spines of equal size and form, doubly forked, each with four thin, bristle-shaped, little divergent teeth. Eight polar spines short, simply forked.

_Dimensions._--Length of the equatorial cross 0.5, breadth 0.4.

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

4. _Zygostaurus caudatus_, n. sp.

Frontal spine (_c_1) very different from the others, pincer-shaped, with two long, nearly parallel slightly bent horns. Lateral spines (_c_2 and _c_4) only half as long, with two short, nearly parallel horns. Caudal spine (_c_3) very long and stout, spindle-shaped, about twice as long as the frontal spine. Eight tropical spines of equal size and form, symmetrical, with two long and thin, divergent horns. Eight polar spines short and stout, with two divergent horns.

_Dimensions._--Length of the equatorial cross 0.8, breadth 0.3.

_Habitat._--Central Pacific, Station 265, surface.

5. _Zygostaurus frontalis_, n. sp.

Frontal spine (_c_1) very different from the others, with two very long, divergent, stout branches. Lateral spines (_c_2 and _c_4) only half as long, each with two stout, nearly parallel horns of equal length. Caudal spine (_c_3) simple, sword-like, shorter than the three former. Eight tropical spines of equal size and form, symmetrical, of the same shape as the two lateral, but only half as large. Eight polar spines very small, rudimentary, each with two short teeth.

_Dimensions._--Length of the equatorial cross 0.7, breadth 0.5.

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

6. _Zygostaurus sagittalis_, n. sp. (Pl. 131, fig. 8).

Frontal spine (_c_1) very different from the others, with two equal, strongly divergent, bent horns. Lateral spines (_c_2 and _c_4) little smaller, but with two very unequal horns (the anterior shorter than the posterior). Caudal spine (_c_3) simple, sword-like or triangular, two-edged, longer {776}than the frontal spine. Eight tropical spines different, the four anterior (_b_1, _b_4, _d_1, _d_4) smaller, with longer horns; the four posterior (_b_2, _b_3, _d_2, _d_3) broader, with shorter horns; the anterior horn of each tropical spine is longer than the posterior. Eight polar spines rudimentary, simple, very short.

_Dimensions._--Length of the equatorial spine-cross 0.6, breadth 0.4.

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

Subfamily 2. LITHOPTERIDA, Haeckel.

_Definition._--#Quadrilonchida# with two opposite transverse apophyses either on all twenty spines or only on a part of them.

Genus 338. _Quadrilonche_,[378] n. gen.

_Definition._--#Quadrilonchida# with two simple opposite apophyses either on each radial spine or only on a part of the twenty spines.

The genus _Quadrilonche_ is the ancestral form of the Lithopterida, or of those Quadrilonchida which bear two opposite apophyses or transverse processes. In _Quadrilonche_ these apophyses are simple, whilst they are branched in _Xiphoptera_ and fenestrated in _Lithoptera_. Each of these three genera may be divided into three subgenera; in the first only the four equatorial spines are provided with apophyses, in the second twelve spines (four equatorial and eight tropical), in the third subgenus all twenty spines.

Subgenus 1. _Quadriloncharium_, Haeckel.

_Definition._--Four large equatorial spines provided with transverse apophyses; sixteen other smaller spines simple, without apophyses.

1. _Quadrilonche tetrastaura_, n. sp.

Four equatorial spines very large, compressed, two-edged, each crossed in the distal third by two opposite simple apophyses. Sixteen other spines also compressed, linear, somewhat shorter than the former and only half as broad, without apophyses.

_Dimensions._--Length of the four major spines 0.12, breadth 0.02; length of the sixteen minor spines 0.08, breadth 0.01.

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

{777}2. _Quadrilonche platystaura_, n. sp. (Pl. 131, fig. 2).

Four equatorial spines lanceolate, compressed, with two opposite triangular simple apophyses in the broadest middle part. Sixteen other spines also lanceolate, much smaller, of about half the length, but only of one-fourth the breadth, without apophyses.

_Dimensions._--Length of the four major spines 0.2, breadth 0.018; length of the sixteen minor spines 0.1, breadth 0.004.

_Habitat._--North Pacific, Station 235, surface.

Subgenus 2. _Quadrilonchidium_, Haeckel.

_Definition._--All twenty spines provided with transverse apophyses.

3. _Quadrilonche mesostaura_, n. sp. (Pl. 131, fig. 1).

Four equatorial spines almost of the some form and length as the sixteen others, but of double or triple the breadth; each spine in its middle third with two opposite broad triangular apophyses, in the basal third rectangular, compressed, in the distal third isosceles triangular, with simple apex.

_Dimensions._--Length of the four major spines 0.16, breadth 0.01 to 0.015; length of the sixteen minor spines 0.12, breadth 0.005.

_Habitat._--Tropical Atlantic, Station 345, surface.

4. _Quadrilonche telostaura_, n. sp.

Four equatorial spines one and a half times as long and three times as broad as the sixteen others; all twenty spines cylindrical, of equal breadth throughout their whole length, with simple conical apex; each spine crossed in the distal third by two opposite, simple, conical apophyses.

_Dimensions._--Length of the four major spines 0.3, breadth 0.012; length of the sixteen minor spines 0.2, breadth 0.004.

_Habitat._--South Atlantic, Station 325, surface.

Genus 339. _Xiphoptera_,[379] Haeckel, 1881, Prodromus, p. 466.

_Definition._--#Quadrilonchida# with two opposite branched (but not latticed) apophyses, either on each radial spine or only on a part of the twenty spines.

The genus _Xiphoptera_ differs from the preceding ancestral genus _Quadrilonche_ in the ramification of the apophyses, which bear perpendicular branches on their distal side. These are therefore parallel to the spine itself. If the branches become united by transverse beams then we get _Lithoptera_.

{778}1. _Xiphoptera tessaractena_, n. sp.

Four equatorial spines in the outer third crossed by two opposite transverse apophyses, each of which bears on its distal side two to three branches, perpendicular to the apophysis and parallel to the spine itself. Sixteen other spines much smaller, in the outer third crossed by two simple opposite transverse apophyses.

_Dimensions._--Length of the four major spines 0.18, of the sixteen minor 0.05 to 0.1.

_Habitat._--North Pacific, Station 238, surface.

2. _Xiphoptera dodecactena_, n. sp. (Pl. 131, fig. 3).

Four equatorial spines one and a half times to twice as long and broad as the eight tropical spines. These twelve spines have the same form and are crossed in their distal third by two large opposite transverse apophyses, each of which bears on its distal side two to four branches, perpendicular to the apophysis and parallel to the spine. Eight polar spines much smaller than the twelve others, simple, without apophyses. The central capsule of this species exhibited a conical protuberance around the base of each individual spine.

_Dimensions._--Length of the twelve larger spines 0.1 to 0.2, of the eight smaller 0.02 to 0.06.

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

3. _Xiphoptera icosactena_, n. sp.

Four equatorial spines about twice as long and four times as broad as the sixteen other spines. All twenty spines crossed in the outer third by two large opposite transverse apophyses, each of which bears on its distal side two to four branches perpendicular to the apophysis and parallel to the spine itself.

_Dimensions._--Length of the four equatorial spines 0.26, of the sixteen smaller 0.11 to 0.14.

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

Genus 340. _Lithoptera_,[380] J. Müller, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 155.

_Definition._--#Quadrilonchida# with two opposite branched and latticed apophyses, either on each radial spine or only on a part of the twenty spines.

The genus _Lithoptera_, founded by Johannes Müller in 1858 for the first observed Mediterranean species, _Lithoptera fenestrata_, differs from all other Quadrilonchida in the fenestrated form of the apophyses, which he compared to the sails of a windmill. This peculiar fenestration is effected by two to four parallel pairs of opposite apophyses, which are crossed by perpendicular branches, parallel to the spine itself. {779}Therefore the wings or lattice-plates have quadrangular meshes and lie in one meridian plane of the spine, not in a tangential plane (as in the _Acanthophracta_). Commonly the lateral ends of the four broad equatorial wings are so crossed that one lateral corner of each wing lies on the upper, the other corner on the under side of both its neighbours; but sometimes the meeting corners have grown together.

Subgenus 1. _Lithopteranna_, Haeckel.

_Definition._--Four equatorial spines with transverse apophyses; sixteen others (eight tropical and eight polar spines) simple, without apophyses.

1. _Lithoptera tetraptera_, n. sp. (Pl. 131, fig. 9).

Four equatorial spines spindle-shaped, with latticed apophyses, each crossed by two transverse beams which are connected at equal distances by four rods parallel to the spine (therefore each wing with four square meshes in a single row). Lateral corners of the neighbouring wings not meeting. Sixteen smaller spines (eight tropical and eight polar) simple, conical, without apophyses.

_Dimensions._--Diagonal of the square body 0.24; length of the inner square 0.16.

_Habitat._--Tropical Atlantic, Station 348, surface.

2. _Lithoptera mülleri_, Haeckel.

_Lithoptera mülleri_, Haeckel, 1862, Monogr. d. Radiol., p. 398, Taf. xx.
figs. 1, 2.

Four equatorial spines four-edged, with large latticed apophyses, each crossed by three transverse beams, which are connected at irregular distances by eight to twelve rods parallel to the spine (therefore each wing with two rows of rectangular meshes). The wings are placed not perfectly in the equatorial plane, but a little obliquely, so that each wing lies with one lateral corner on the upper, with the other corner on the under side of its neighbours. Sixteen smaller spines simple, thin, cylindrical, without apophyses.

_Dimensions._--Diagonal of the square body 0.3; length of the inner square 0.17.

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

3. _Lithoptera lamarckii_, n. sp.

Four equatorial spines four-edged, with large latticed apophyses; each crossed by three transverse beams, which are connected at short distances by twelve to sixteen rods parallel to the spine (therefore each wing with two rows of hexagonal or nearly elliptical meshes). Wings placed as in _Lithoptera mülleri_. Sixteen smaller spines simple, thin, prismatic, without apophyses.

_Dimensions._--Diagonal of the square body 0.35; length of the inner square 0.2.

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

{780}4. _Lithoptera tetragona_, n. sp.

Four equatorial spines compressed, four-edged, with large latticed apophyses, each crossed by four transverse beams, which are connected at regular distances by eight to twelve rods parallel to the spine. (Therefore each wing with three rows of square meshes.) Wings placed in the equatorial plane and grown together by their meeting lateral ends, forming a square equatorial girdle of lattice-work. Sixteen smaller spines simple, thin, prismatic, without apophyses.

_Dimensions._--Diameter of the square body 0.4; length of the inner square 0.22.

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

Subgenus 2. _Lithopterella_, Haeckel.

_Definition._--Twelve spines (four equatorial and eight tropical) with transverse apophyses; the eight polar spines simple, without apophyses.

5. _Lithoptera quadrata_, n. sp. (Pl. 131, fig. 10).

Twelve spines with transverse apophyses; eight (polar) spines simple, small, without apophyses. Four equatorial spines very large and stout, compressed, each crossed by four transverse beams, which are connected by eight to ten rods parallel to the spine (therefore each wing with three rows of irregular rectangular meshes). Wings placed in the equatorial plane and grown together by their meeting lateral ends, forming a square equatorial girdle of lattice-work. Eight tropical spines thin, crossed by a long and thin transverse beam, which bears on its distal side eight to ten rods parallel to the spine.

_Dimensions._--Diagonal of the square body 0.35; length of the inner square 0.18.

_Habitat._--South Atlantic, Station 326, surface.

6. _Lithoptera dodecaptera_, n. sp.

Twelve spines with transverse apophyses; eight (polar) spines simple, small, without apophyses. Four equatorial spines very large, quadrangular; each crossed by three transverse beams, which are connected by ten to twelve rods parallel to the spine (therefore each wing with two rows of square meshes). Wings placed as in _Lithoptera mülleri_. Eight tropical spines much thinner, crossed each by two transverse beams, which are connected by six to eight rods parallel to the spine (therefore each wing with one row of rectangular meshes).

_Dimensions._--Diagonal of the square body 0.4; length of the inner square 0.25.

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

Subgenus 3. _Lithopteromma_, Haeckel.

_Definition._--All twenty spines with transverse apophyses.

{781}7. _Lithoptera darwinii_, Haeckel.

_Lithoptera darwinii_, Haeckel, 1879, Natürl. Schöpfungsgesch., Aufl.
vii. p. 706, Taf. xvi. fig. 12.

All twenty spines with transverse apophyses; these are quite simple in the eight small cross-shaped polar spines; also simple, but bearing some perpendicular rods, in the eight thin tropical spines. Four equatorial spines very large and stout, each crossed by four transverse beams, which are connected by eight to ten rods parallel to the spine (therefore each wing with three rows of irregular rectangular meshes). Wings placed in the equatorial plane and grown partly together by their meeting lateral ends.

_Dimensions._--Diagonal of the square body 0.4; length of the inner square 0.2.

_Habitat._--South-east Pacific, west coast of Patagonia, Station 302, surface.

8. _Lithoptera icosaptera_, n. sp.

All twenty spines with transverse apophyses, bearing one to three rows of rectangular meshes; eight polar spines small, each with a single row; eight tropical spines long and thin, each with two parallel rows. Four equatorial spines much larger and thicker, each with three parallel transverse rows of meshes. All twenty wings free, not grown together by their lateral ends.

_Dimensions._--Diagonal of the square body 0.48; length of the inner square 0.24.

_Habitat._--Indian Ocean, Belligemma, Ceylon (Haeckel), surface.

9. _Lithoptera fenestrata_, J. Müller.

_Lithoptera fenestrata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 154, Taf. xi. fig. 13.

All twenty spines with transverse apophyses, bearing one to three rows of irregular, rectangular meshes; eight polar and eight tropical spines small, each with a single row of meshes (between two parallel transverse beams). Four equatorial spines little larger, each with two rows (between three parallel transverse beams). Central capsule filled up with green pigment.

_Dimensions._--Diagonal of the square body 0.3; length of the inner square 0.2.

_Habitat._--Mediterranean (Saint Tropez, Nice).

Family XXXVIII. #AMPHILONCHIDA#, Haeckel (Pl. 132).

_Acantholonchida_ (Amphilonchida et Amphilithida), Haeckel, 1881, Prodromus, p. 466.

_Definition._--ACANTHARIA with twenty radial spines of very unequal size, disposed according to the law of the Icosacantha; two opposite equatorial spines (in the longitudinal axis) much larger than the eighteen others. No lattice-shell.

The family #Amphilonchida# is distinguished from all other #Acanthometra# by the excessive development of two opposite equatorial spines, which are much larger {782}than the eighteen other spines. In my Monograph (1862, p. 389) I had united all these Acanthonida in a single genus _Amphilonche_ (with ten species). Some species of it are very common and widely distributed; but in general the number of different forms in this family is much smaller than in the two foregoing families.

The two principal spines, which in all Amphilonchida are much larger than the eighteen other spines, characterise the "hydrotomical axis" or the larger equatorial axis. The two other equatorial spines or the "geotomical spines" are much smaller, and commonly of the same size as the eight tropical and the eight polar spines. In the genera _Amphilonche_ and _Amphibelone_ these eighteen smaller spines are rather equally developed; sometimes they are very small or quite rudimentary, so that the skeleton seems to be represented only by the two very long principal spines (Pl. 132, fig. 4). The genus _Acantholonche_ is distinguished by the unequal size of the eight tropical and the eight polar spines, the latter being more or less rudimentary. However, the central bases of all twenty spines, by which they are united in the centre, are constantly present. The genus _Amphibelone_ is distinguished by the unequal size and form of the two principal spines, one of them the "caudal spine," being larger (and often of another form) than the opposite "frontal spine."

The form of the radial spines is in the Amphilonchida far less varied and complicated than in the other Acanthonida (the Astrolonchida and Quadrilonchida). Apophyses or lateral transverse processes are never developed. The three main forms of spines are the same as in the other Acanthonida; they are (1) either cylindrical or conical (like _Acanthometron_), or (2) compressed or two-edged (like _Zygacantha_), or (3) quadrangular or four-edged (like _Acanthonia_). Often the spines are angular in the inner or proximal, roundish in the outer or distal part. The distal apex is commonly simple, conical or pyramidal. The central base is commonly also pyramidal, as in the majority of the Acanthonida; and the triangular faces of the neighbouring bases are simply propped one upon another. More rarely a basal leaf-cross is developed above the basal pyramid. Very rarely the central bases of the united spines grow together in the centre, so that the whole skeleton forms a single piece of acanthin.

_The Central Capsule_ is rarely spherical, commonly prolonged in the direction of the hydrotomical axis; ellipsoidal or cylindrical, sometimes also four-sided prismatic; it commonly envelops the greater part of the two principal spines; its structure and contents are the same as in the other Acanthonida.

_Synopsis of the Genera of Amphilonchida._

{ Two opposite large
{ principal spines
Eighteen smaller spines { (frontal and caudal)
of nearly equal size { equal, 341. _Amphilonche_.
and similar form. {
{ Caudal spine larger than
{ the frontal spine, 342. _Amphibelone_.

Eight tropical and eight polar spines of different
sizes (the latter often rudimentary), 343. _Acantholonche_.

{783}Genus 341. _Amphilonche_,[381] Haeckel, 1862, Monogr. d. Radiol., p. 389.

_Definition._--#Amphilonchida# with two equal principal spines (frontal and caudal spines not different); the eighteen smaller spines nearly equal.

The genus _Amphilonche_ represents the original and at the same time the most common form of Amphilonchida; the two opposite principal spines are of equal size and form, much larger (and often also of another form) than the eighteen smaller spines; these latter exhibit no marked differences in size and form.

Subgenus 1. _Amphiloncharium_, Haeckel.

_Definition._--Spines in the centre united by triangular faces of their pyramidal bases, propped one upon another. No basal leaf-cross.

1. _Amphilonche belonoides_, Haeckel.

_Amphilonche belonoides_, Haeckel, 1862, Monogr. d. Radiol., p. 392, Taf.
xvi. fig. 6, Taf. xviii. fig. 21.

_Acanthometra belonoides_, Haeckel, 1860, Monatsber. d. k. Akad. d. Wiss.
Berlin, p. 808.

Two principal spines cylindrical, of equal breadth throughout their whole length, with simple conical apex; base a small pyramid, without leaf-cross. Eighteen smaller spines conical, much shorter, with simple bristle-shaped apex. Central capsule spindle-shaped or cylindrical, yellow.

_Dimensions._--Length of the two major spines 0.4 to 0.8, of the eighteen minor 0.05 to 0.2.

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

2. _Amphilonche lanceolata_, n. sp. (Pl. 132, fig. 1).

Two principal spines compressed, lanceolate, two-edged, gradually tapering from the broader middle towards the two ends; apex simple; base a large pyramid, with broad leaf-cross. Eighteen smaller spines about half as long, pyramidal, with simple conical or bristle-shaped apex. Central capsule lentelliptical, pink, opaque.

_Dimensions._--Length of the two major spines 0.2, of the eighteen minor 0.1.

_Habitat._--Tropical Atlantic, Station 343, surface.

3. _Amphilonche diodon_, n. sp. (Pl. 132, fig. 3).

Two principal spines compressed, lanceolate, two-edged, tapering from the broader middle towards the two ends; apex simple; base a small pyramid, without leaf-cross. Eighteen smaller spines {784}sword-shaped, only two-thirds or one-half as long, and one-third or one-fourth as broad, each with two opposite teeth in the distal part. Central capsule ellipsoidal.

_Dimensions._--Length of the two major spines 0.13, breadth 0.02; length of the eighteen minor spines 0.1.

_Habitat._--North Atlantic, Station 352, surface.

4. _Amphilonche tenuis_, Haeckel.

_Amphilonche tenuis_, Haeckel, 1862, Monogr. d. Radiol., p. 389, Taf.
xvi. fig. 1, Taf. xviii. fig. 16.

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

Two principal spines quadrangular prismatic, with smooth edges, slightly or not at all prominent, of equal breadth throughout their whole length; apex simple or bifid; base a small pyramid, without leaf-cross. Eighteen smaller spines of the same form, but only one-fourth or one-third as long. Central capsule spherical or ellipsoidal, colourless.

_Dimensions._--Length of the two major spines 0.2 to 0.3, of the eighteen minor spines 0.05 to 0.1.

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

5. _Amphilonche denticulata_, Haeckel.

_Amphilonche denticulata_, Haeckel, 1862, Monogr. d. Radiol., p. 390,
Taf. xvi. fig. 2, Taf. xviii. fig. 17.

Two principal spines quadrangular prismatic, with prominent, elegantly denticulated edges, of equal breadth throughout their whole length; apex simple or truncated; base a small pyramid, without leaf-cross. Eighteen smaller spines of the same form, but only one-fourth or one-third as long. Central capsule ellipsoidal, opaque, yellowish-brown.

_Dimensions._--Length of the two major spines 0.3 to 0.4, of the eighteen minor 0.1; breadth of the former 0.009, of the latter 0.006.

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

6. _Amphilonche heteracantha_, Haeckel.

_Amphilonche heteracantha_, Haeckel, 1862, Monogr. d. Radiol., p. 293,
Taf. xvi. fig. 7.

_Acanthometra heteracantha_, Haeckel, 1860, Monatsber. d. k. Akad. d.
Wiss. Berlin, p. 808.

Two principal spines quadrangular prismatic, very large, with four broad, prominent, lamellar edges, of equal breadth throughout their whole length. Apex as well as the base a four-sided pyramid. Eighteen smaller spines very thin, conical, with bristle-shaped apex; base a small pyramid, without leaf-cross. Central capsule cylindrical or violin-shaped, opaque yellow.

_Dimensions._--Length of the two major spines 0.2 to 0.3, breadth 0.015 to 0.02; length of the eighteen minor spines 0.1 to 0.15, basal breadth 0.004 to 0.008.

_Habitat._--Mediterranean (Messina); Central Pacific, Station 271, surface.

{785}7. _Amphilonche elongata_, Haeckel.

_Amphilonche elongata_, Haeckel, 1862, Monogr. d. Radiol., p. 392, Taf.
xviii. figs. 22_a_, 22_b_.

_Acanthometra elongata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 48, Taf. vii. fig. 13.

Two principal spines quadrangular prismatic in the proximal half, cylindrical or spindle-shaped in the distal half, with simple apex; base a small pyramid, without leaf-cross. Eighteen smaller spines very thin, bristle-shaped, conical on the base, with small pyramid. Central capsule spindle-shaped, transparent, yellow.

_Dimensions._--Length of the two major spines 0.3 to 0.5, breadth 0.01 to 0.03; length of the eighteen smaller spines 0.05 to 0.3.

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

Subgenus 2. _Amphilonchidium_, Haeckel.

_Definition._--Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; between the meeting edges of the latter twenty-two pyramidal compartments or basal funnels.

8. _Amphilonche ovata_, Haeckel.

_Amphilonche ovata_, Haeckel, 1862, Monogr. d. Radiol., p. 390.

_Acanthometra ovata_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 47, Taf. vii. fig. 10, Taf. ix. fig. 4.

Two principal spines cylindrical, of equal breadth throughout their whole length, with simple conical or bifid apex; base with a large leaf-cross of double the breadth. Eighteen smaller spines of the same form, but thinner and only half as long. Central capsule ellipsoidal, brown, opaque.

_Dimensions._--Length of the two major spines 0.3 to 0.4, breadth 0.008 to 0.012; length of the eighteen minor spines 0.1 to 0.2.

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

9. _Amphilonche conica_, n. sp. (Pl. 132, fig. 6).

Two principal spines conical, elongate, with simple apex; base thickened, with large leaf-cross. Eighteen smaller spines also conical, of about the same basal breadth, but only one-fourth to one-half as long. Central capsule ellipsoidal, pellucid.

_Dimensions._--Length of the two major spines 0.15 to 0.2, basal breadth 0.03 to 0.04; length of the eighteen minor spines 0.05 to 0.1.

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

{786}10. _Amphilonche lancetta_, n. sp.

Two principal spines compressed, lanceolate, two edged, gradually tapering from the broader middle towards the two ends; apex simple; base of double the breadth, with a large leaf-cross. Eighteen smaller spines of the same form, but shorter and only half as broad. Central capsule lentelliptical, pellucid.

_Dimensions._--Length of the two major spines 0.2 to 0.3, breadth in the middle part 0.02 to 0.03; length of the eighteen smaller spines 0.1 to 0.2.

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

11. _Amphilonche complanata_, Haeckel.

_Amphilonche complanata_, Haeckel, 1862, Monogr. d. Radiol., p. 390, Taf.
xvi. fig. 3, Taf. xviii. fig. 18, _a_, _b_.

_Acanthometra complanata_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 808.

Two principal spines compressed, two-edged, linear, of equal breadth throughout their whole length; apex emarginate or bifid; base with a large leaf-cross of double the breadth. Eighteen smaller spines of the same form, but only one-fourth to one-half as large. Central capsule ellipsoidal, yellow, pellucid.

_Dimensions._--Length of the two major spines 0.15 to 0.25, breadth 0.004 to 0.006; length of the eighteen minor spines 0.05 to 0.1.

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

12. _Amphilonche messanensis_, Haeckel.

_Amphilonche messanensis_, Haeckel, 1862, Monogr. d. Radiol., p. 391,
Taf. xvi. fig. 4, Taf. xviii. fig. 19.

_Acanthometra messanensis_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 808.

Two principal spines quadrangular prismatic, often a little compressed from two sides, of nearly equal breadth throughout their whole length; apex either truncate or emarginate, with two opposite teeth; base with a large leaf-cross of double the breadth. Eighteen smaller spines of similar form or more compressed, much shorter. Central capsule spherical or ellipsoidal, yellow, transparent.

_Dimensions._--Length of the two major spines 0.12 to 0.18, breadth 0.016; length of the minor spines 0.05 to 0.09.

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

13. _Amphilonche hydrotomica_, n. sp. (Pl. 132, fig. 2).

Two principal spines quadrangular prismatic, with four broad prominent lamellar edges or wings, of equal breadth throughout their whole length; apex pyramidal; base with a large leaf-cross. Eighteen smaller spines cylindrical or bristle-shaped, only half as long and very thin. Central capsule cylindrical or spindle-shaped, very long, opaque.

{787}_Dimensions._--Length of the two major spines 0.1 to 0.2, breadth 0.02 to 0.03; length of the eighteen minor spines 0.05 to 0.1.

_Habitat._--Central Pacific, Stations 270 to 274, surface.

14. _Amphilonche violina_, n. sp. (Pl. 132, fig. 5).

Two principal spines quadrangular prismatic, nearly violin-shaped, with four very broad, prominent, lamellar wings, which are constricted in the middle part, and broadened towards the two ends; apex truncate pyramidal; base with a large leaf-cross. Eighteen smaller spines much shorter, of equal breadth at the base, assuming the form of a quadrangular pyramid, thin prismatic in the distal half. Central capsule spindle-shaped, opaque.

_Dimensions._--Length of the two major spines 0.15 to 0.18, breadth 0.02 to 0.025; length of the eighteen minor spines 0.04 to 0.08.

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

15. _Amphilonche tetraptera_, Haeckel.

_Amphilonche tetraptera_, Haeckel, 1862, Monogr. d. Radiol., p. 391, Taf.
xvi. fig. 5, Taf. xviii. fig. 20.

_Acanthometra tetraptera_, Haeckel, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 808.

Two principal spines four-sided pyramidal, with four broad lamellar prominent edges; apex simple or bifid; base with a large leaf-cross. Eighteen smaller spines of similar form, but only half as large. Central capsule spherical, opaque.

_Dimensions._--Length of the two major spines 0.2, breadth on the base 0.025; length of the eighteen minor spines 0.1.

_Habitat._--Mediterranean (Messina); North Atlantic, Canary Islands, Stations 352 to 354, surface.

Subgenus 3. _Amphilithium_, Haeckel, 1881, Prodromus, p. 466.

_Definition._--Spines in the basal part grown together, so that the whole skeleton represents a single piece of acanthin; a star with two larger and eighteen smaller rays.

16. _Amphilonche concreta_, n. sp. (Pl. 132, figs. 4, 4_a_).

Two principal spines cylindrical, very long, of equal breadth throughout their whole length, with simple conical apex. Eighteen smaller spines short, conical or bristle-shaped, scarcely one-fourth or one-tenth as long, often quite rudimentary. All twenty spines perfectly grown together in the centre, forming a single piece of acanthin (derived from _Amphilonche belonoides_ by central concrescence; often the sutures of the concreted bases are visible, fig. 4_a_).

_Dimensions._--Length of the two major spines 0.1 to 0.4, breadth 0.005 to 0.015; length of the eighteen minor spines 0.005 to 0.15.

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

{788}17. _Amphilonche acufera_, n. sp.

Two principal spines thick, four-sided prismatic in the basal half, cylindrical or spindle-shaped in the distal half, with simple conical apex. Eighteen smaller spines shorter, thin, bristle-shaped or conical on the base. All twenty spines in the centre perfectly grown together, forming a single piece of acanthin. (Derived from _Amphilonche elongata_ by central concrescence.)

_Dimensions._--Length of the two major spines 0.3 to 0.5, breadth 0.01 to 0.03; length of the eighteen minor spines 0.08 to 0.2.

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

Genus 342. _Amphibelone_,[382] Haeckel, 1862, Monogr. d. Radiol., p. 392.

_Definition._--#Amphilonchida# with two unequal principal spines (the frontal spine very different from the caudal spine); the eighteen smaller spines nearly equal.

The genus _Amphibelone_ exhibits among the Amphilonchida the same remarkable differentiation of the two principal or longitudinal spines, as _Zygostaurus_ among the Quadrilonchida; the frontal spine differs commonly from the caudal spine not only in its size, but also in its peculiar form; commonly one pole of the longitudinal axis is much more strongly developed than the other. The eighteen smaller spines are nearly equal.

Subgenus 1. _Amphibelonium_, Haeckel.

_Definition._--All twenty spines separate, but in contact in the centre and resting one against another by the triangular sides of their pyramidal bases, without a prominent basal leaf-cross.

1. _Amphibelone aciculata_, n. sp.

Two principal spines thick, without edges and wings, the frontal spine short, spindle-shaped, the caudal three to six times as long, cylindrical, both of equal breadth, with simple conical apex and simple pyramidal base, without leaf-cross. Eighteen smaller spines very thin, bristle-shaped, of the same length as the frontal spine. Central capsule cylindrical or spindle-shaped, enveloping the two principal spines nearly throughout their whole length.

_Dimensions._--Length of the frontal spine 0.2 to 0.4, of the caudal spine 1.0 to 2.0; breadth of both 0.01; length of the eighteen smaller spines 0.1 to 0.3.

_Habitat._--South Atlantic, Station 325, surface.