Chapter XI: Literature and History (38)

Apophyses of the long polar and tropical spines crossed by a transverse beam, which is again crossed by two perpendicular branches parallel to the apophyses; these branches are united by concrescence, and form a square shield with four crossed pores, the centre of which is pierced by the spine. At the base of each spine (in the outer shell) four crossed aspinal pores, corresponding to those of the shield, of about the same size as the other roundish pores. Four equatorial spines, simple, without apophyses, somewhat larger than the other sixteen spines.

_Dimensions._--Diameter of the outer shell 0.1, of the inner 0.04.

_Habitat._--Indian Ocean, Sunda-Archipelago, Singapore, Trebing, surface.

----

Suborder II. PRUNOPHRACTA.

_Definition._--Shell ellipsoidal, lenticular or diploconical, with radial beams of different size.

Family XLII. #BELONASPIDA#, n. fam. (Pl. 136, figs. 6-9; Pl. 139, figs. 8, 9).

_Definition._--ACANTHARIA with a simple ellipsoidal lattice-shell, composed of the branched apophyses of twenty radial spines meeting in its centre and disposed according to the Müllerian law of Icosacantha. Two opposite equatorial spines larger than the two others. Central capsule ellipsoidal, enclosed in the fenestrated shell.

The family #Belonaspida#, formerly united by me with the Dorataspida (in the Prodromus, 1881, p. 468), differs from it in the ellipsoidal form of the lattice-shell and {860}the enclosed central capsule. In the spherical Dorataspida, their ancestral family, all twenty radial spines are of equal size, whilst here in the Belonaspida two opposite spines are larger than the eighteen others. These two larger or principal spines are both equatorial spines, placed in the longitudinal or major axis of the ellipsoid, or the "hydrotomical axis" (compare above, p. 719). The two other equatorial spines are constantly smaller, and lie in the transverse or minor axis of the ellipsoid, or the "geotomical axis." The geometrical proportion of these two determining axes of the ellipsoidal shell is very variable (even in one and the same species), commonly 4 : 3 or 3 : 2, rarely 2 : 1, often only 5 : 4 or 6 : 5. All meridian planes, passing through the principal spines (or the longitudinal axis of the shell) are elliptical, and of equal size. All transverse planes, perpendicular to that axis, are circular; the largest of these circular parallel planes is the geotomical plane, which passes through the smaller equatorial spines and the spineless axis.

In the spherical Dorataspida the internal length of the radial spines (or the distance between the shell and the centre) is equal in all twenty spines. In the ellipsoidal Belonaspida this internal length is different, and commonly exhibits four different degrees; in the two principal spines it is of first rank, in the eight tropical spines of second rank, in the four (hydrotomical) polar spines of third rank, and in the six spines (four geotomical polar spines and two transverse equatorial spines) of fourth rank. These differences of the internal length become more important the more the hydrotomical axis is prolonged. Regarding all other qualities (in form, disposition, and mode of junction at the centre) the ellipsoidal Belonaspida do not differ from their ancestral group, the spherical Dorataspida (compare above, p. 802). In both families the pyramidal central bases of the twenty spines are commonly supported one upon another with their triangular neighbouring faces; but sometimes also here (particularly in _Phatnaspis_) the central bases are perfectly grown together. In this case also the sutures of the meeting branches of the apophyses are obliterated, whilst usually they remain open. Such forms, with spines and plates perfectly grown together, form a single piece of acanthin, and were formerly separated by me as a peculiar genus _Haliommatidium_ (Monogr. d. Radiol., 1862, p. 419). But as I now find this concrescence to be an accidental and inconstant peculiarity of some species, it no longer seems to me to be of generic importance.

The apophyses of the twenty radial spines, the branches of which compose the ellipsoidal lattice-shell, exhibit in all Belonaspida the same appearance as in the Diporaspida (and especially the Ceriaspida) among the spherical Dorataspida. Everywhere each radial spine gives off only two opposite primary apophyses, the fork-branches of which unite together and form a plate or shield with two aspinal pores (as in _Dorataspis_). Commonly the shell exhibits only these forty parmal pores, the other meshes between them being sutural pores. Only in one genus, _Phatnaspis_ (Pl. 136, {861}figs. 6-9), is this number multiplied; the two opposite primary apophyses are here crossed by numerous perpendicular lateral branches, and these are again united by secondary perpendicular ramules which are parallel to the apophyses themselves; therefore each plate here forms a rhombic shield pierced by very numerous (often more than one hundred) small quadrangular or circular pores. Only two of these numerous parmal pores are the primary aspinal pores (sometimes, as in Pl. 136, fig. 8, distinguished by their larger size); all others are secondary or coronal pores. Therefore _Phatnaspis_ repeats the characteristic formation of _Coscinaspis_, from which it differs in its ellipsoidal shell.

Moreover, the four other genera of the ellipsoidal Belonaspida correspond perfectly to certain genera of the spherical Dorataspida, and may be derived from these by hypertrophy or stronger development of two opposite equatorial spines. In _Thoracaspis_ and _Belonaspis_ (Pl. 139, figs. 8, 9) the surface of the shell-plates is without crests and dimples (in the former without, in the latter with accessory by-spines); they thus correspond to _Dorataspis_ and _Diporaspis_ among the Dorataspida. In two other genera the surface of the shell-plates bears a network of elevated crests, separating funnel-shaped dimples, in _Dictyaspis_ without, in _Coleaspis_ with by-spines; these correspond to _Ceriaspis_ and _Hystrichaspis_ among the Dorataspida. The small by-spines, covering the surface, exhibit the same forms as in the Dorataspida; but they are usually smaller, and less developed in the Belonaspida.

The twenty radial spines are commonly more or less compressed or two-edged, sometimes very flat, broad, and triangular (Pl. 139, figs. 8, 9). In some species (mainly of _Phatnaspis_) they are very long, thin, and needle-shaped (Monogr. d. Radiol., 1862, Taf. xxii. figs. 10-12). Rarely they are cylindrical, four-edged, or prismatic. The Belonaspida testify by this and other peculiarities to their near relation to the Diporaspida and Phractacanthida and their older origin from _Zygacantha_.

_The Central Capsule_ is in the Belonaspida ellipsoidal, and more or less prolonged in the hydrotomical or longitudinal axis of the shell. It is constantly smaller than the enveloping ellipsoidal shell, and separated from it by the calymma. Its structure and the shape of its nucleus are the same as in the nearly allied Dorataspida.

_Synopsis of the Genera of Belonaspida._

-------------------------------------------------------------------------
I. Subfamily Coleaspida.
Forty parmal pores (two aspinal pores on each plate, no coronal
pores).
-------------------------------------------------------------------------
Plates not dimpled, without { No by-spines, 371. _Thoracaspis_.
prominent crests. {
{ With by-spines, 372. _Belonaspis_.

Plates dimpled, with a { No by-spines, 373. _Dictyaspis_.
network of prominent {
crests, { With by-spines, 374. _Coleaspis_.
-------------------------------------------------------------------------
II. Subfamily Phatnaspida.
Eighty to two thousand or more parmal pores (two aspinal pores on
each plate, surrounded by two to one hundred or more coronal pores).
-------------------------------------------------------------------------
No by-spines (plates not dimpled), 375. _Phatnaspis_.

{862}Genus 371. _Thoracaspis_,[411] Haeckel, 1862, Prodromus, p. 468.

_Definition._--#Belonaspida# with forty parmal pores (two on each plate), without dimples and crests, also without by-spines, therefore with smooth surface.

The genus _Thoracaspis_ is the simplest form among the Belonaspida, and repeats in this family the nearly allied genus _Dorataspis_ among the Dorataspida. It differs from this genus only in the characteristic prolongation of one equatorial axis, which effects an ellipsoidal transformation of the spherical central capsule and the enclosing lattice-shell.

1. _Thoracaspis ellipsoides_, n. sp.

Parmal pores large, elliptical, five or six times as large as the small circular sutural pores. Each plate surrounded by five or six sutural pores (a single one on each side). Spines compressed triangular, sword-like, two-edged; inner and outer half of nearly equal length.

_Dimensions._--Length of the ellipsoidal shell (or major axis) 0.15, breadth (or minor axis) 0.12; length of the spines 0.07, basal breadth 0.016.

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

2. _Thoracaspis nephropora_, n. sp.

Parmal pores large, kidney-shaped, three to four times as large as the roundish small sutural pores. Each plate surrounded by five or six sutural pores (a single one on each side). Spines in the inner longer part cylindrical, in the outer shorter part conical, not compressed.

_Dimensions._--Length of the shell 0.2, breadth 0.15; length of the spines 0.06, basal breadth 0.018.

_Habitat._--Central Pacific, Station 268, surface.

3. _Thoracaspis circopora_, n. sp.

Parmal pores circular, of the same size as the circular sutural pores. Each plate surrounded by five or six sutural pores (a single one on each side). Spines compressed, thin, linear, two-edged; outer part one and a half times as long as the inner.

_Dimensions._--Length of the shell 0.17, breadth 0.13; length of the spines 0.12, basal breadth 0.003.

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

4. _Thoracaspis bipennis_, n. sp. (Pl. 139, fig. 8).

Parmal pores elliptical, about twice as large as the circular sutural pores, which are of rather variable size. Each plate surrounded by eight to twelve sutural pores (commonly two on each side). {863}Spines compressed, triangular, gradually tapering towards both ends; outer half a little longer, and much broader than the inner.

_Dimensions._--Length of the shell 0.14, breadth 0.12; length of the spines 0.08, basal breadth 0.025.

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

Genus 372. _Belonaspis_,[412] Haeckel, 1862, Prodromus, p. 468.

_Definition._--#Belonaspida# with forty parmal pores (two on each plate), without dimples and crests, but with numerous by-spines on the surface.

The genus _Belonaspis_ differs from its ancestral genus _Thoracaspis_ only in the possession of numerous superficial by-spines, and bears therefore to it the same relation as _Diporaspis_ does to _Dorataspis_. The two latter differ from the two former in the spherical form of the central capsule and the enclosing shell, which here becomes ellipsoidal.

1. _Belonaspis pandanus_, n. sp.

Parmal pores elliptical, three or four times as large as the circular sutural pores. Each plate surrounded by five or six sutural pores (a single one on each side). Spines compressed, triangular; outer part half as long as the inner, and twice as long as the numerous, simple, bristle-shaped by-spines.

_Dimensions._--Length of the ellipsoidal shell (or major axis) 0.12, breadth (or minor axis) 0.1; length of the spines 0.03, basal breadth 0.02.

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

2. _Belonaspis furcata_, n. sp.

Parmal pores elliptical, twice as broad as the circular sutural pores. Each plate surrounded by five or six sutural pores (a single one on each side). Spines compressed, linear, very thin; outer part longer than the inner. By-spines very numerous, half as long as the radius, furcate, with divergent fork-branches.

_Dimensions._--Length of the shell 0.1, breadth 0.08; length of the spines 0.12, breadth 0.003.

_Habitat._--Indian Ocean (Cocos Islands), Rabbe, surface.

3. _Belonaspis datura_, n. sp. (Pl. 139, fig. 9).

Parmal pores elliptical, three or four times as large as the circular sutural pores. Each plate surrounded by ten or twelve sutural pores (two on each side). Spines triangular, two-edged, about {864}as long as the radius of the shell; gradually tapering from its surface towards both ends. By-spines very short and numerous, simple.

_Dimensions._--Length of the shell 0.13, breadth 0.11; length of the spines 0.08, basal breadth 0.025.

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

4. _Belonaspis lanceolata_, n. sp.

Parmal pores elliptical, six or eight times as large as the small circular sutural pores. Each plate surrounded by ten to twelve sutural pores (two on each side). Spines lanceolate, flat, in the distal part needle-shaped, about as long as the diameter of the shell. By-spines very numerous, zigzag, half as long as the shell-radius.

_Dimensions._--Length of the shell 0.15 breadth 0.13; length of the spines 0.14, basal breadth 0.03; length of the by-spines 0.04.

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

5. _Belonaspis conifera_, n. sp.

Parmal pores kidney-shaped, three or four times as large as the small circular pores. Each plate surrounded by ten to twelve sutural pores (two on each side). Spines very thick, half as long in the outer conical part as in the inner cylindrical part. By-spines very short, conical.

_Dimensions._--Length of the shell 0.2, breadth 0.16; length of the spines 0.05, basal breadth 0.03.

_Habitat._--Central Pacific, Station 267, surface.

6. _Belonaspis multiforis_, n. sp.

Parmal pores circular, of the same size as the circular sutural pores. Each plate surrounded by fifteen to eighteen sutural pores (three on each side). Spines compressed, about as long as the radius. By-spines very numerous, zigzag, half as long as the radius.

_Dimensions._--Length of the shell 0.22, breadth 0.18; length of the spines 0.12, basal breadth 0.012; length of the by-spines 0.06.

_Habitat._--Equatorial Atlantic, Station 347, surface.

Genus 373. _Dictyaspis_,[413] n. gen.

_Definition._--#Belonaspida# with forty parmal pores (two on each plate), without by-spines, but with a network of prominent crests on the dimply surface.

The genus _Dictyaspis_ repeats among the Belonaspida the characteristic structure of _Ceriaspis_ (among the Dorataspida), by the development of prominent crests forming a {865}network with dimples on the outer surface of the shields. Either all the dimples or only a part of them are pierced by a pore. The forty aspinal pores are united in pairs in twenty larger dimples. The shell is usually very thick-walled and non-transparent.

1. _Dictyaspis solidissima_, Haeckel.

_Dorataspis solidissima_, Haeckel, 1862, Monogr. d. Radiol., p. 416, Taf.
xxii. figs. 6-9.

Surface of the shell with seventy to eighty funnel-shaped dimples, each of which is perforated at the base by one or two small meshes; twenty larger dimples in the centre of the plates (each with two elliptical aspinal pores), and fifty to sixty smaller sutural dimples between them (each with a single circular pore). All pores of nearly the same size. No blind dimples. Outer conical part of the thick radial spines of the same length as the inner cylindrical part. Radius of the shell four times as large as the thickness of its wall.

_Dimensions._--Length of the shell 0.12, breadth 0.1; length of the spines 0.06, basal breadth 0.012.

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

2. _Dictyaspis favosa_, n. sp.

Surface of the shell with one hundred and seventy to one hundred and ninety deep funnel-shaped dimples, seventy to eighty of which are perforated, the others blind; among the former each of the fifty to sixty smaller contains a single sutural pore, each of the twenty larger a couple of aspinal pores. All pores of nearly the same size. Outer part of the compressed two-edged spines triangular, half as long as the inner part. Radius of the shell six times as large as the thickness of its wall. (Differs from _Ceriaspis favosa_, Pl. 138, fig. 6, mainly in the ellipsoidal form of the shell and the different size and form of the spines.)

_Dimensions._--Length of the shell 0.16, breadth 0.13; length of the spines 0.04, basal breadth 0.025.

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

3. _Dictyaspis compacta_, n. sp.

Surface of the shell with one hundred and seventy to one hundred and ninety deep funnel-shaped dimples, seventy to eighty of which are perforated, the others blind; among the former each of fifty to sixty each contain a single sutural pore, twenty each a couple of aspinal pores. All dimples nearly of the same size, very deep. Outer part of the compressed sword-like spines somewhat longer than the inner part. Radius of the dark shell only twice as large as the thickness of its compact wall.

_Dimensions._--Length of the shell 0.18, breadth 0.15; length of the spines 0.12, basal breadth 0.02.

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

{866}Genus 374. _Coleaspis_,[414] Haeckel, 1881, Prodromus, p. 468.

_Definition._--#Belonaspida# with forty parmal pores (two on each plate), with numerous by-spines and with a network of prominent crests on the dimpled surface.

The genus _Coleaspis_ differs from its ancestral genus _Dictyaspis_ in the development of numerous by-spines, and bears therefore among the ellipsoidal Belonaspida the same relation to it as _Hystrichaspis_ does to _Coscinaspis_ among the spherical Dorataspida. If the four equatorial spines in _Coleaspis_ become different in pairs, it passes over into _Hexalaspis_. The shell is usually very dark and thick-walled.

1. _Coleaspis coronata_, n. sp.

All twenty spines of nearly equal size and form, about as long as the radius of the shell, compressed, sword-like, two-edged; both equatorial spines of the hydrotomical axis little longer than the eighteen others. Crests between the dimples of the shell-surface dentated, forming around the basal half of each spine a cylindrical sheath with a dentated, crown-like mouth, the teeth of which are prolonged into simple by-spines. (Similar to _Hexaconus coronatus_, Pl. 139, fig. 5, but differing in the nearly equal size of the spines and their sheaths, and in the longer by-spines.)

_Dimensions._--Major axis of the shell 0.2, minor 0.17; length of the spines 0.12, basal breadth 0.02.

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

2. _Coleaspis vaginata_, n. sp. (Pl. 140, fig. 13).

All twenty spines of nearly equal size and form, nearly as long as the diameter of the shell, conical; both equatorial spines of the hydrotomical axis about one-third longer than the eighteen others. Crests between the dimples of the shell-surface serrated, forming around the basal half of each spine a conical truncate sheath with crested surface and serrated mouth, the teeth of which are prolonged into short by-spines. (Similar to _Hexaconus vaginatus_, Pl. 139, fig. 7, but differing in the nearly equal size of all the spines and in the double thickness of the shell-wall.)

_Dimensions._--Major axis of the shell 0.12, minor 0.1, length of the spines 0.08, basal breadth 0.01.

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

3. _Coleaspis obscura_, n. sp.

All twenty spines of nearly equal size and form, little longer than their large cylindrical sheaths, which are nearly as long as the radius of the shell, and armed on the truncated mouth with strong triangular by-spines, both equatorial spines of the hydrotomical axis one and a half times as long as the eighteen others. Shell very dark and thick walled, quite opaque.

{867}_Dimensions._--Major axis of the shell 0.1, minor 0.08; length of the spines 0.06, of their sheaths 0.04.

_Habitat._--Arctic Ocean, Greenland, Koch, surface.

4. _Coleaspis occulta_, n. sp.

All twenty spines of nearly equal size and form, quite concealed in their long cylindrical sheaths, which are somewhat longer than the radius of the shell, and armed on the truncated mouth with acute simple teeth; each sheath deeply sulcated, apparently resulting from the concrescence of numerous parallel leaf-shaped by-spines. Small shell very dark and thick-walled, quite opaque.

_Dimensions._--Major axis of the shell 0.08, minor 0.06; length of the spines and their sheaths 0.05 to 0.06.

_Habitat._--Antarctic Ocean (off Kerguelen), Station 159, surface.

Subgenus 2. _Coleaspidium_, Haeckel.

_Definition._--Both equatorial spines of the hydrotomical axis much larger and of peculiar form, different from the eighteen other spines.

5. _Coleaspis amphilonche_, n. sp.

Both equatorial spines of the hydrotomical axis much longer than the eighteen others, and of very different form; one and a half times as long as the diameter of the shell, prismatic, with six prominent edges, pyramidal at the distal point. The eighteen other spines triangular, compressed, two-edged, scarcely as long as the radius of the thick-walled shell. Pores of the shell irregular polygonal, separated by ciliated crests, which bear simple by-spines (one-third as long as the radius).

_Dimensions._--Major axis of the shell 0.15, minor 0.12; length of the two larger spines 0.22, of the eighteen smaller 0.06 to 0.08; basal breadth of the former 0.03, of the latter 0.008.

_Habitat._--South Atlantic, Station 341, surface.

6. _Coleaspis hydrotomica_, n. sp. (Pl. 140, fig. 14).

Both equatorial spines of the hydrotomical axis much larger than the eighteen others, and of very different form; about as long as the diameter of the shell, in the basal half four-sided pyramidal, with four thick prominent edges, in the middle part constricted, in the distal half lanceolate, two-edged. Both equatorial spines of the geotomical axis of similar form, but much smaller, scarcely one-third as long. The sixteen other spines sword-like, thin, two-edged, about as long as the radius of the thick-walled shell. Pores of the shell irregular roundish, separated by high dentated crests, which bears zigzag by-spines (half as long as the radius).

_Dimensions._--Major axis of the shell 0.12, minor axis 0.1; length of the two larger spines 0.11, of the eighteen others 0.04 to 0.06; basal breadth of the former 0.04, of the latter 0.01.

_Habitat._--Cape of Good Hope, Station 143, surface.

{868}Genus 375. _Phatnaspis_,[415] Haeckel, 1881, Prodromus, p. 468

_Definition._--#Belonaspida# with eighty to two thousand or more parmal pores (four to one hundred or more on each plate), without by-spines on the surface.

The genus _Phatnaspis_ corresponds to the spherical _Coscinaspis_ among the Dorataspida, and differs from the other Belonaspida in the great number of the parmal pores; whilst the four other preceding genera exhibit only two opposite aspinal pores in the centre of each plate, in this there are constantly numerous coronal pores in addition to these, and the plates always possess the characteristic form of a wainscotted or panelled work, with quadrangular meshes. The number of these parmal pores amounts in each plate to from ten to twenty, often one hundred and twenty or more; therefore the number of parmal pores in the whole shell amounts to two thousand or more. Sometimes the pores are circular, but in this case too they are surrounded by quadrangular frames. The quadrangles are sometimes quite regular squares, sometimes more or less irregular. The thin and fragile bars between the quadrangular pores form in each plate two peculiar systems of parallel crests, which cross at right angles. Commonly the parallel crests of one system (parallel to the major diameter of the compressed radial spines) are equidistant, and pierce from one edge of the plate to the opposite, whilst the parallel crests of the other system (parallel to the minor diameter of the spines) are interrupted and at different distances (Pl. 136, fig. 9); but in other species both crossed systems are quite regular. In each plate there is one primary diagonal rib (often stronger than the parallel crests) which connects the two opposite corners of the rhomboidal plate. We can distinguish in this genus three different subgenera: A. in _Phatnasparium_ the primary diagonal rib arises from both flat sides of the compressed sword-like, radial spines; B. in _Phatnasplenium_ from both sharp edges of them; C. in _Phatnaspidium_ two crossed diagonal ribs arise from four edges of the spines (combination of A and B). Therefore in the first subgenus (A) two primary aspinal pores are placed opposite on the sharp edges of the spines, but in the second (B) inversely on their flat sides; in the third (C) there are apparently four primary aspinal pores, which are probably derived from B or A by division of the two pores.

Subgenus 1. _Phatnasparium_, Haeckel.

_Definition._--In the centre of each rhomboidal plate two primary aspinal pores, opposite on both edges of the compressed spines, from both flat sides of which the primary diagonal crest arises.

{869}1. _Phatnaspis lacunaria_, n. sp. (Pl. 136, fig. 9).

Parmal pores irregular quadrangular, of unequal size and form, ten to twelve on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores opposite on both edges of the latter. Spines much compressed, sword-like, their outer half shorter than the inner.

_Dimensions._--Length of the shell 0.21 to 0.23, breadth 0.18 to 0.2; basal breadth of the spines 0.01.

_Habitat._--Central Pacific, Station 268, surface.

2. _Phatnaspis ensiformis_, n. sp.

Parmal pores irregular quadrangular, of unequal size and form, six to eight on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores opposite on the two edges of the latter. Spines very broad, strongly compressed, sword-like, their outer half larger than the inner.

_Dimensions._--Length of the shell 0.16, breadth 0.11; basal breadth of the spines 0.02.

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

3. _Phatnaspis loculata_, n. sp.

Parmal pores regular quadrangular, of nearly equal size and form, twelve to sixteen on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores on the two edges of the latter. Spines linear, compressed, very long and thin, their outer half three to four times as long as the inner.

_Dimensions._--Length of the shell 0.24, breadth 0.18; breadth of the spines 0.004.

_Habitat._--North Atlantic, Station 354, surface.

4. _Phatnaspis fenestrata_, Haeckel.

_Haliommatidium fenestratum_, Haeckel, 1862, Monogr. d. Radiol., p. 421.

Parmal pores regular quadrangular, of nearly equal size and form, six to eight on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores on the two edges of the latter. Spines linear, little compressed, or nearly needle-shaped, very long and thin, their outer half five to ten times as long as the inner.

_Dimensions._--Length of the shell 0.11 to 0.12, breadth 0.07 to 0.08; breadth of the spines 0.002.

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

5. _Phatnaspis cristata_, n. sp. (Pl. 136, fig. 6).

Parmal pores circular, of very different size, separated by high square crests, ten to twelve on each side of the high, comb-like, primary diagonal rib, which arises from both flat sides of the {870}twoedged spines; two primary aspinal pores on the two edges of the latter. Each circular pore is surrounded by a square frame. Spines sword-like, strongly compressed, their outer part longer than the inner.

_Dimensions._--Length of the shell 0.2 to 0.22, breadth 0.16 to 0.18; basal breadth of the spines 0.01.

_Habitat._--North Pacific, Station 254, surface.

6. _Phatnaspis coscinoides_, n. sp.

Parmal pores circular, regular, all of nearly equal size, twelve to sixteen on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary pores on the two edges of the latter. Spines linear, little compressed, their outer part much longer than the inner.

_Dimensions._--Length of the shell 0.18, breadth 0.15; breadth of the spines 0.006.

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

Subgenus 2. _Phatnasplenium_, Haeckel.

_Definition._--In the centre of each rhomboidal plate two primary aspinal pores, opposite on the two flat sides of the compressed spines, from the two edges of which the primary diagonal crest arises.

7. _Phatnaspis orthopora_, n. sp.

Parmal pores irregular quadrangular, of unequal size and form, four to six on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two larger primary aspinal pores opposite on the two flat sides of the latter. Spines very thin and long, linear, their outer half three to four times as long as the inner.

_Dimensions._--Length of the shell 0.08, breadth 0.06; breadth of the spines 0.003.

_Habitat._--North Atlantic, Station 353, surface.

8. _Phatnaspis polypora_, n. sp.

Parmal pores irregular polygonal, of very unequal size and form, sixteen to twenty on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two very large, lanceolate, primary aspinal pores opposite on the two flat sides of the latter. Spines very thin, linear, on the outside of the shell rudimentary. (This remarkable species somewhat resembles _Coscinaspis polypora_, Pl. 136, fig. 8.)

_Dimensions._--Length of the shell 0.32, breadth 0.24; breadth of the spines 0.002.

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

{871}9. _Phatnaspis quadratura_, n. sp.

Parmal pores regular, square, all of nearly equal size and form, ten to twelve on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two primary aspinal pores opposite on the two flat sides of the latter, not different from the other pores. Spines sword-like, their outer part about as long as the inner.

_Dimensions._--Length of the shell 0.2, breadth 0.16; basal breadth of the spines 0.004.

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

10. _Phatnaspis tabulata_, Haeckel.

_Haliomma tabulatum_, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 37, Taf. v. figs. 5-8.

_Haliomma tabulatum_, Haeckel, 1862, Monogr. d. Radiol., p. 429.

Parmal pores regular, circular, with square frames, all of nearly equal size, eight to ten on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two primary aspinal pores opposite on the flat sides of the latter. Spines sword-like, short, scarcely half as long as the radius of the shell, their central ends are thickened and cause by their union the deceptive appearance of an enclosed "medullary shell."

_Dimensions._--Length of the shell 0.12 to 0.15, breadth 0.1 to 0.12; breadth of the spines 0.006.

_Habitat._--Mediterranean; Nice, Müller; Portofino, near Genoa, Haeckel, surface.

Subgenus 3. _Phatnaspidium_, Haeckel.

_Definition._--In the centre of each rhomboidal plate four primary aspinal spines, forming a regular cross, the centre of which receives the cylindrical or four-sided prismatic spine.

11. _Phatnaspis haliommidium_, n. sp. (Pl. 136, fig. 7).

Parmal pores irregular quadrangular, of unequal size and form, eight to ten on each side of the crossed diagonal ribs, which arise at right angles from the four edges of the prismatic spines; four primary aspinal pores not different from the others. Outer part of the strong spines scarcely longer than the inner. (Resembling _Icosaspis tabulata_, Pl. 136, fig. 2, which, however, is distinguished by the spherical shell and the larger pores.)

_Dimensions._--Length of the shell 0.22, breadth 0.17; breadth of the spines 0.016.

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

12. _Phatnaspis mülleri_, n. sp.

_Haliommatidium mülleri_, Haeckel, 1862, Monogr. A. Radiol, p. 419, pl.
xiii. figs. 10-12.

Parmal pores regular, square, all of nearly equal size and form, twelve to sixteen on each side of the crossed diagonal ribs, which arise at right angles from the needle-shaped spines; the four {872}primary aspinal pores not different from the others. Spines very thin and long, cylindrical; four to six times longer in the outer than in the inner part.

_Dimensions._--Length of the shell 0.24, breadth 0.16; breadth of the spines 0.002.

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

Family XLIII. #HEXALASPIDA#, n. fam. (Pl. 139).

_Definition._--ACANTHARIA with a simple discoidal or lenticular lattice-shell, composed of the branched apophyses of twenty radial spines meeting in the centre and disposed according to the Müllerian law of Icosacantha. Six larger spines in the hydrotomical plane, prominent on the margin of the circular or elliptical biconvex lens. Fourteen other spines much smaller or rudimentary. Central capsule biconvex lenticular, enclosed in the fenestrated shell.

The family #Hexalaspida# represents a new small, but very interesting group of Acanthophracta, which differs from all others in the lentelliptical or triaxial form of the lenticular lattice-shell, the margin of which bears six larger spines placed in the hydrotomical plane (compare above, p. 719). They may therefore be characterised shortly as "_Acanthophracta lentelliptica_," with three different dimensive axes and six larger marginal spines. A closer comparison with the other ACANTHARIA leaves no doubt that the Hexalaspida must be derived from the Belonaspida by stronger development of six radial spines placed in the hydrotomical plane, namely, two equatorial and four associated polar spines; whilst the six spines of the geotomical plane (perpendicular to the former) are much smaller; the eight tropical spines are intermediate in size between the former and the latter.

The geometrical fundamental form of the Hexalaspida (of the central capsule as well as of the enclosing shell) is therefore lentelliptical, with three different dimensive axes, and they exhibit among the ACANTHARIA a relation to the spherical Dorataspida and the ellipsoidal Belonaspida similar to that which the lentelliptical #Larcoidea# exhibit to the spherical #Sphæroidea# and the ellipsoidal #Prunoidea# among the #Sphærellaria# (compare above, p. 599). The largest of the three dimensive axes (which are perpendicular to one another) is here the hydrotomical axis, the shortest, on the contrary, the geotomical axis; the intermediate in size being the spineless axis. The development of the whole body is strongest in the hydrotomical meridian plane, in which the six principal spines are placed; it is weakest in the geotomical plane, in which the six smallest spines are placed; the eight tropical spines are intermediate in size between the others. This peculiar development is illustrated by the figures of Pl. 139, where the four equatorial spines are everywhere marked by _c_, the eight tropical spines by _b_ and _d_, the eight polar spines by _a_ and _e_.

{873}Rarely the six hydrotomical or principal spines are of equal size, and thus the margin of the shell may be quite circular or regularly hexagonal (Pl. 139, figs. 1-3); the two equatorial spines of the hydrotomical plane are usually larger than its four polar spines, and thus the margin of the shell becomes more or less elliptical (Pl. 139, figs. 4-7). Usually (almost constantly) these six larger spines are more or less compressed, triangular, often very broad and flat; their two edges lie in the hydrotomical plane. Their two flat surfaces are often furrowed, with longitudinal ribs or crests converging towards the simple apex of the spines.

The fourteen smaller spines are regularly disposed according to the Müllerian law of Icosacantha on both convex sides of the lenticular shell; they are not only smaller than the six principal spines, but often also of different form, much thinner and shorter, sometimes needle-shaped. In the genera _Hexonaspis_ and _Hexacolpus_ (Pl. 139, figs. 1, 2) only their inner part (inside of the shell) is developed, whilst their outer part is quite rudimentary and not prominent on the surface. Therefore these genera appear to possess only six marginal spines externally.

_The Lenticular Shell_ itself offers in the Hexalaspida great difficulties in the way of accurate study, as its wall is constantly very thick and dark, often quite opaque and non-transparent. However, prolonged accurate researches have convinced me that its structure is essentially the same as in the Belonaspida and especially in the genera _Dictyaspis_ and _Coleaspis_. As in these latter the twenty plates of the shell bear high crests or combs on the outer surface, and by these funnel-shaped dimples are separated. The network of these crests is more or less regular (Pl. 139, figs. 1-7). Around the base of each radial spine the shell is usually elevated in the form of a conical or cylindrical sheath; the crests are prolonged into the sheaths as longitudinal ribs, parallel to the spine or convergent towards its apex. Whilst in _Hexalaspis_ and _Hexonaspis_ these basal sheaths are not at all or but little prominent (Pl. 139, fig. 2; Pl. 140, fig. 16), in _Hexaconus_ and _Hexacolpus_ they envelop the basal half (or even more) of the spines, and very often the circular or elliptical free distal edge of the sheath is elegantly denticulated or serrated (Pl. 139, figs. 1, 3-7; pl. 140, figs. 9-16).

_The Pores_ of the shell exhibit in the Hexalaspida the same shape as in the majority of the Belonaspida. Each spine bears only two broad opposite apophyses, the fork-branches of which unite to form a polygonal shield with two pores. The number of parmal pores is constantly (?) forty, as each plate possesses only two primary aspinal pores; there are no secondary or coronal pores. The numerous (between fifty and one hundred, rarely more) smaller pores between the forty parmal pores are probably always sutural pores; however, their number and position is very difficult to determine, on account of the high protecting crests; the majority of the funnel-shaped dimples between the latter seem to be blind, not perforated. Sometimes all the dimples, except the twenty spinal ones, seem to be blind and the sutural pores appear {874}to have disappeared completely, so that there remain only twenty aspinal pores (Pl. 139, fig. 4).

The internal cavity of the shell in all Hexalaspida is very small, on account of the thickness of the massive wall; the latter is often greater than the diameter of the cavity. Setting aside this disproportion, the space of the cavity is further much reduced by the internal parts of the thick radial spines, which are united in the centre by their pyramidal bases (Pl. 140, fig. 15). Usually the twenty bases seem to remain free (supported one upon another by means of their triangular faces); but sometimes they seem to grow together perfectly and to form a single central star of acanthin. In some species, too, the sutures of the meeting branches of the apophyses of neighbouring spines seem to grow together, so that the whole shell exhibits a single piece of acanthin.

_The Central Capsule_ of the Hexalaspida is therefore very small and seems to fill up the greatest part of the shell-cavity. Its form is constantly more or less lenticular, sometimes lentelliptical. On account of the opacity of the shell I could not make out its shape more closely.

_Synopsis of the Genera of Hexalaspida._

All twenty spines externally } Sheaths of the spines
developed, prominent on } not prominent, 376. _Hexalaspis_.
the surface of the }
lenticular shell. } Sheaths of the spines
} prominent, 377. _Hexaconus_.

Only six spines (the }
hydrotomical spines) } Sheaths of the spines
externally developed and } not prominent, 378. _Hexonaspis_.
prominent on the margin }
of the disk; the other } Sheaths of the spines
fourteen spines not } prominent, 379. _Hexacolpus_.
prominent. }

Genus 376. _Hexalaspis_,[416] n. gen.

_Definition._--#Hexalaspida# with twenty prominent radial spines, which are not surrounded by prominent sheaths; the six hydrotomical spines much larger than the fourteen others.

The genus _Hexalaspis_ is the simplest form among the Hexalaspida, and may be derived directly from _Dictyaspis_ among the Belonaspida, by stronger development of the six hydrotomical spines. As in the following genus _Hexaconus_ all twenty spines are prominent externally.

Subgenus 1. _Hexalasparium_, Haeckel.

_Definition._--Six hydrotomical spines of equal size.

{875}1. _Hexalaspis heliodiscus_, n. sp. (Pl. 139, fig. 2).

All six hydrotomical spines of nearly equal size (or sometimes the two equatorial a little larger than the four polar spines), isosceles triangular, compressed, smooth; about as long as the radius of the shell, and half as broad at the base. The fourteen other spines very small, also triangular and compressed, but little prominent on the two convex sides of the lenticular shell.

_Dimensions._--Diameter of the shell 0.11; length of the six hydrotomical spines 0.05, basal breadth 0.03.

_Habitat._--Central Pacific, Station 271 to 274, surface.

2. _Hexalaspis stellata_, n. sp.

All six hydrotomical spines of nearly equal size, lanceolate compressed, with two longitudinal furrows on each flat side, about as long as the diameter of the shell, and one-fourth as broad at the base. The fourteen other spines very thin, also compressed, half as long and only one-fourth as broad as the six large spines.

_Dimensions._--Diameter of the shell 0.14; length of the six hydrotomical spines 0.13, basal breadth 0.035.

_Habitat._--South Pacific, Station 284, surface.

Subgenus 2. _Hexalaspidium_, Haeckel.

_Definition._--Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

3. _Hexalaspis sexalata_, n. sp.

Six hydrotomical spines of unequal size; the two equatorial spines about as long as the shell-radius and twice as long as the four polar spines, which are isosceles triangular. The fourteen other spines are only half as long and one-fourth as broad as the latter, little prominent. (Resembles _Hexonaspis hastata_, Pl. 140, fig. 16, which is distinguishable by the furrows on the six spines and by the total absence of the fourteen external rudimentary spines.)

_Dimensions._--Diameter of the shell 0.15; length of the two equatorial spines 0.08, of the four polar spines 0.04, of the fourteen other spines 0.02.

_Habitat._--North Pacific, Station 240, surface.

4. _Hexalaspis hexalastrum_, n. sp.

Six hydrotomical spines of unequal size; the two equatorial spines somewhat longer than the diameter of the shell and three times as long as the four polar spines, all six triangular, smooth, of the same basal breadth (equal to half the radius). The fourteen other spines very thin, conical at the base, nearly as long as the radius.

{876}_Dimensions._--Diameter of the shell 0.21; length of the two equatorial spines 0.24, of the eighteen others 0.08 to 0.1; basal breadth of the six larger spines 0.05, of the fourteen others 0.01.

_Habitat._--Western Tropical Pacific, Station 224, surface.

5. _Hexalaspis hexaglypha_, n. sp.

Six hydrotomical spines of unequal size; the two equatorial very large, six-sided prismatic, twice as long as the diameter of the shell and four times as long as the four pyramidal polar spines; each of these six spines with six deep furrows between the six prominent edges. The fourteen other spines very thin, compressed, two-edged, about as long as the radius of the shell.

_Dimensions._--Diameter of the shell 0.11; length of the two equatorial spines 0.2, of the eighteen others 0.04 to 0.06; basal breadth of the six larger spines 0.03, of the fourteen others 0.01.

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

Genus 377. _Hexaconus_,[417] n. gen.

_Definition._--#Hexalaspida# with twenty prominent radial spines, which are surrounded at the base by prominent sheaths; the six hydrotomical spines much larger than the fourteen others.

The genus _Hexaconus_ differs from the preceding _Hexalaspis_ in the development of conical or cylindrical sheaths surrounding the basal parts of the radial spines; these sheaths are developed sometimes around all twenty spines, sometimes only around the six larger hydrotomical spines.

Subgenus 1. _Hexaconarium_, Haeckel.

_Definition._--Six hydrotomical spines of equal size.

1. _Hexaconus ciliatus_, n. sp. (Pl. 139, fig. 3).

All six hydrotomical spines of nearly equal size, pyramidal, with six prominent edges, somewhat longer than the radius of the shell. Sheaths sulcated, finely ciliated at the mouth, twice as broad as long and only one-fourth as long as the spines. The fourteen smaller spines very thin, bristle-shaped, shorter than the radius of the shell.

_Dimensions._--Diameter of the shell 0.16; length of the six hydrotomical spines 0.11; basal breadth 0.03.

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

{877}2. _Hexaconus coronatus_, n. sp. (Pl. 139, fig. 5).

All six hydrotomical spines of equal size, conical, somewhat compressed, with two prominent edges, scarcely as long as the radius of the shell. Sheaths crested, strongly dentated on the mouth, three times as broad as long and only one-sixth as long as the spines. Fourteen smaller spines about half as large as the six principal spines, of the same form, but without coronated sheaths.

_Dimensions._--Diameter of the shell 0.2; length of the six hydrotomical spines 0.1; basal breadth 0.02.

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

3. _Hexaconus velatus_, n. sp. (Pl. 139, fig. 6).

All six hydrotomical spines of equal size, conical, somewhat compressed, shorter than the radius of the shell. Sheaths very large, truncated conical, enveloping the spines almost entirely, with crested wall, only half as broad at the constricted mouth as at the base. The fourteen smaller spines about half as large as the six principal spines, of the same form, but without large sheaths.

_Dimensions._--Diameter of the shell 0.12; length of the six hydrotomical spines 0.05; basal breadth 0.01.

_Habitat._--North Atlantic, Station 354, surface.

Subgenus 2. _Hexaconidium_, Haeckel.

_Definition._--Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

4. _Hexaconus serratus_, n. sp. (Pl. 139, fig. 4).

Six hydrotomical spines of unequal size, the two equatorial being as long as the radius of the shell and one and a half times as large as the four polar; all of the same form, triangular, compressed, with six prominent edges. Sheaths cylindrical, half as long as the spines, with prominent crests, and with strong serrated teeth at the distal mouth. The fourteen smaller spines scarcely one-fourth or one-sixth as large as the six principal spines, without prominent sheaths.

_Dimensions._--Diameter of the shell 0.2; length of the equatorial spines 0.1, basal breadth 0.05; length and breadth of the sheaths 0.05.

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

5. _Hexaconus vaginatus_, n. sp. (Pl. 139, fig. 7).

Six hydrotomical spines of unequal size; the two equatorial very stout, pyramidal, six-edged, nearly as long as the diameter of the shell, and on the base three to four times as broad as the eighteen other spines, which are much thinner, all nearly of equal length, and two-edged. All {878}twenty spines are provided with prominent basal sheaths, which are truncate conical, sulcate, and dentate on the narrowed distal mouth. The sheaths of the six hydrotomical spines are twice to three times as large as those of the fourteen smaller spines.

_Dimensions._--Diameter of the shell 0.15; length of the spines 0.12; basal breadth of the equatorial spines 0.04, of the other spines 0.02; length of the hydrotomical sheaths 0.05, of the other sheaths 0.02.

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

6. _Hexaconus echinatus_, n. sp. (Pl. 140, fig. 12).

Six hydrotomical spines of unequal size; the two equatorial, and their sheaths twice as large as the four polar spines. These six spines are six-edged, pyramidal, and their basal half enveloped by very large conical sheaths which are sulcate, and twice as broad on the dentate distal mouth as on the narrower base. The other fourteen spines are very thin, two-edged, half as long, with low sheaths. Approaches some forms of _Diploconus_.

_Dimensions._--Diameter of the shell 0.15; length of the equatorial spines 0.13, of the polar spines 0.08.

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

Genus 378. _Hexonaspis_,[418] n. gen.

_Definition._--#Hexalaspida# with six prominent radial spines (in the hydrotomical plane) which are not surrounded by prominent sheaths; the fourteen other spines quite rudimentary, not prominent.

The genus _Hexonaspis_ and the following _Hexacolpus_ differ from the two preceding genera in the rudimentary shape of the fourteen reduced and stunted smaller spines; these are only developed inside the shell, and are not prominent outside over its surface.

Subgenus 1. _Hexonasparium_, Haeckel.

_Definition._--Six hydrotomical spines of equal size.

1. _Hexonaspis heliosestrum_, n. sp.

All six hydrotomical spines of nearly equal size, isosceles triangular, compressed, smooth, about as long as the diameter of the shell and three times as long as broad at the base. This species is very similar to _Hexalaspis heliodiscus_ (Pl. 139, fig. 2), but differs in the larger size of the six marginal spines and in the complete external absence of the fourteen smaller spines.

{879}_Dimensions._--Diameter of the shell 0.13; length of the six marginal spines 0.12, basal breadth 0.04.

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

2. _Hexonaspis hexapleura_, n. sp. (Pl. 140, fig. 15).

All six hydrotomical spines of nearly equal size, triangular, compressed, six-edged, about as long as the radius of the shell and twice as long as broad on the base. Two strong prominent ribs on each flat side of the spines. Shell very thick-walled, with a very small cavity.

_Dimensions._--Diameter of the shell 0.11; length of the six marginal spines 0.06, basal breadth 0.03.

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

3. _Hexonaspis hexagona_, n. sp.

All six hydrotomical spines of equal size, very short, triangular, only half as long as broad at the base. The whole shell accordingly forms a regular hexagon, the six corners of which are formed by the distal points of the rudimentary spines, the six sides by their straight lateral edges. Shell very dark.

_Dimensions._--Diameter of the shell 0.2; length of the six marginal spines 0.03, basal breadth 0.06.

_Habitat._--South Atlantic (east of Patagonia), Station 318, surface.

Subgenus 2. _Hexonaspidium_, Haeckel.

_Definition._--Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

4. _Hexonaspis hastata_, n. sp. (Pl. 140, fig. 16).

Six hydrotomical spines of unequal size; two larger equatorial spines with six prominent wings, about as long as the radius of the shell and half as broad at the base; the four polar spines quite as broad, but only half as long, nearly equilateral triangular, with two shallow furrows on each flat side at the broader base. The fourteen smaller spines not visible on the surface, quite rudimentary. Crests of the surface elegantly denticulated.

_Dimensions._--Diameter of the shell 0.14; length of the two equatorial spines 0.08, of the four polar spines 0.04; basal breadth 0.04.

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

{880}Genus 379. _Hexacolpus_,[419] n. gen.

_Definition._--#Hexalaspida# with six prominent radial spines (in the hydrotomical plane), which are surrounded by prominent sheaths at the base; the fourteen other spines quite rudimentary, not prominent.

The genus _Hexacolpus_ differs from the preceding _Hexonaspis_ in the development of conical or cylindrical sheaths around the basal parts of the radial spines. It bears to the latter the same relation as _Hexaconus_ exhibits to _Hexalaspis_.

Subgenus 1. _Hexacolparium_, Haeckel.

_Definition._--Six hydrotomical spines all nearly of equal size.

1. _Hexacolpus nivalis_, n. sp. (Pl. 139, fig. 1).

_Hexalaspis nivalis_, Haeckel, 1882, Manuscript et Atlas.

All six hydrotomical spines of nearly equal size and equidistant, thin, lanceolate, compressed, somewhat shorter than the diameter of the hexagonal shell. Sheaths nearly prismatic, conical in the distal third, each with twelve prominent parallel crests, which are separated by twelve deep furrows; their contracted distal opening or mouth denticulate. The sheaths are as long as the radius of the shell, and envelop two-thirds of the spines. (Resembles certain forms of snow-crystals.)

_Dimensions._--Diameter of the shell 0.15, thickness of its wall 0.08; length of the spines 0.1, of the sheath 0.007; breadth of the latter 0.04.

_Habitat._--West Tropical Pacific, Station 225, surface.

2. _Hexacolpus conifer_, n. sp.

All six hydrotomical spines of equal size and equidistant, triangular, compressed, about as long as the radius of the circular shell. Sheaths conical, sulcate, half as broad on the serrate distal end as on the base. The sheaths envelop the basal half of the spines.

_Dimensions._--Diameter of the shell 0.18; length of the spines 0.1, of the sheaths 0.06; basal breadth of the latter 0.07, distal breadth 0.04.

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

Subgenus 2. _Hexacolpidium_, Haeckel.

_Definition._--Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

{881}3. _Hexacolpus trypanon_, n. sp. (Pl. 140, fig. 11).

Six hydrotomical spines of unequal size, two equatorial about as long as the diameter of the shell and nearly twice as large as the four polar; all of the same form, quadrangular prismatic, with prominent edges and pointed distal ends. Sheaths six-sided prismatic, with strong prominent edges and thinner parallel ribs between them; their distal mouth with six strong denticulated teeth. The sheaths envelop two-thirds of the spines, and are as broad as the radius of the shell.

_Dimensions._--Diameter of the shell 0.13; length of the equatorial spines 0.12, of their sheaths 0.08; breadth of the latter 0.06.

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

4. _Hexacolpus dodecodus_, n. sp.

Six hydrotomical spines of unequal size, two equatorial about as long as the radius of the shell and twice as large as the four polar; all of the same form, triangular, compressed, sulcated. Sheaths prismatic, with twelve prominent, parallel edges, and twelve strong serrated triangular teeth on the mouth. The sheaths envelop the basal half of the spines. This species greatly resembles _Hexaconus serratus_ (Pl. 139, fig. 4), but differs in the larger size of the equatorial spines and the complete reduction of the fourteen smaller spines.

_Dimensions._--Diameter of the shell 0.2; length of the equatorial spines 0.1, of their sheaths 0.06; breadth of the latter 0.08.

_Habitat._--North Pacific, Station 248, surface.

5. _Hexacolpus infundibulum_, n. sp. (Pl. 140, fig. 10).

Six hydrotomical spines of unequal size, two equatorial about twice as long as the diameter of the shell and as the four polar spines; all six spines of the same form, quadrangular prismatic, pointed at the distal pyramidal end. Sheaths conical, two to three times as broad at the denticulate distal mouth as at the narrow base, sulcate; the mantle of the cone concavely vaulted. The large sheaths envelop two-thirds or three-fourths of the spines.

_Dimensions._--Diameter of the shell 0.1 to 0.13; length of the equatorial spines 0.15 to 0.2, of their sheaths 0.1 to 0.15; basal breadth of the latter 0.04, distal breadth 0.12.

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

Family XLIV. #DIPLOCONIDA#, Haeckel (Pl. 140).

_Diploconida_, Haeckel, 1862, Monogr. d. Radiol., p.404.

_Definition._--ACANTHARIA with simple diploconical shell, composed of two very large equatorial spines which are opposite in the hydrotomical axis, are surrounded by conical or cylindrical, often compressed sheaths, and arise from a small central {882}lattice-shell. Eighteen other spines (disposed according to the Müllerian law of Icosacantha) much smaller, often rudimentary. Central capsule ellipsoidal or diploconical.

The family #Diploconida#, founded by me in 1862 for a single Mediterranean species (_Diploconus fasces_), appears to be the most aberrant and strange form among the ACANTHARIA. As I had met with only a single specimen, very dark and intransparent in its central part, my observations on its structure were imperfect and the explanation of it partly erroneous (compare my Monograph, pp. 46, 404, Taf. xx. figs. 7, 8). However, I regarded _Diploconus_ as the representative of quite a peculiar family, derived from the Acanthometrida, and I correctly compared the large opposite radial spines of one equatorial axis with the corresponding parts in _Amphilonche_.

Afterwards Richard Hertwig observed some specimens of _Diploconus fasces_ in the same locality (Messina), and gave an accurate description of its central capsule, including numerous small nuclei (1879, Organismus d. Radiol., p. 28, Taf. ii. fig. 3). He found also that the peculiar diploconical skeleton is not composed of silex, but of acanthin. In the explanation of the shell-structure he adopted my opinion.

In the rich collections of the Challenger I detected ten different forms of Diploconida, all very rare, and for the most part represented only by single specimens. A twelfth species was found by me in the collection of Captain Rabbe from the Indian Ocean. By the study of these new forms, and particularly by their comparison with the most nearly allied Hexalaspida and Belonaspida, it was possible for me to correct some errors in my former description and to give a much more correct description and natural explanation of this very peculiar and strange family of Radiolaria (compare Pl. 140).