Chapter XIX: Section II: DICYRTIDA, Haeckel, 1862, Monogr. d. Radiol., pp. 280, 296 (5)

No horn, 580. _Dicolocapsa_.
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Cephalis hidden in the upper part of the thorax.
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No horn, 581. _Cryptocapsa_.

Subfamily 1. SETHOCORIDA, Haeckel, Prodromus, p. 430.

_Definition._--#Sethocyrtida# with the basal mouth of the shell open (vel Dicyrtida eradiata aperta).

{1290}Genus 572. _Sethoconus_,[189] Haeckel, 1881, Prodromus, p. 430.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with conical or campanulate, gradually dilated thorax and wide open mouth. Cephalis with one or more horns.

The genus _Sethoconus_ is the oldest and simplest form of the Sethocorida, or of those Dicyrtida in which the simple thorax bears no apophyses and has the mouth open and not closed by a basal lattice-plate. Probably all those eradiate Sethocorida have been derived either from triradiate Sethopilida (_Lychnocanium_), or from multiradiate Sethophormida (_Sethophormis_, _Anthocyrtis_ ?) by loss of the radial ribs and feet. In _Sethoconus_ the thorax is more or less conical, sometimes more campanulate, commonly smooth, in some species covered with spines. The cephalis is usually small, with rudimentary collar septum, at other times large, with distinct cortinar septum. Correspondingly, the genus may be divided into different groups, which here are enumerated as subgenera.

Subgenus 1. _Conarachnium_, Haeckel, 1881, Prodromus, p. 430. (= _Ceratocyrtis_, Bütschli), 1882, _loc. cit._, p. 536.

_Definition._--Cephalis relatively large, with distinct collar septum and numerous pores. Thorax smooth.

1. _Sethoconus trochus_, Haeckel.

_Eucyrtidium trochus_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 293, Taf. vii, fig. 17.

_Conarachnium trochus_, Haeckel, 1881, Prodromus, p. 430.

Cephalis ovate, relatively large, with a pyramidal horn of the same length, and three pairs of large opposite pores, on each side of a vertical septum. Thorax wide, conical, about as long as broad, with nearly straight outlines; its pores regular, circular, hexagonally framed, of the same size as the cephalic pores.

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax 0.06 long, 0.06 broad.

_Habitat._--Tropical Pacific, Stations 200 to 281, surface.

2. _Sethoconus cucullaris_, Haeckel.

_Cornutella cucullaris_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. ii. fig. 7.

_Ceratocyrtis cucullaris_, Bütschli, 1882, Zeitschr. f. wiss Zool., Bd.
xxvi. p. 536, Taf. xxxiii. fig. 36, _a._, _b._

Cephalis subspherical, thorny, relatively large, with a conical horn of the same length, and small circular pores. Thorax wide, conical, enveloping the lower hidden half of the cephalis, about as {1291}long as broad, with slightly convex outlines; its pores subregular, circular, half as broad as the cephalis.

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax 0.15 long, 0.14 broad.

_Habitat._--Fossil in Barbados.

3. _Sethoconus pileus_, n. sp.

Cephalis subspherical, free, with distinct collar stricture, a conical oblique horn of the same length, and small, irregular, roundish pores. Thorax flatly conical, about half as long as broad, with straight outlines; its pores subregular, hexagonal, half as broad as the cephalis, with very thin bars.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.08 long, 0.16 broad.

_Habitat._--Central Pacific, Stations 262 to 274, surface.

4. _Sethoconus ampliatus_, Haeckel.

_Cornutella ampliata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. ii. fig. 5.

_Ceratocyrtis ampliata_, Bütschli, 1882, Zeitschr. f. wiss. Zool., Bd.
xxxvi. p. 536.

Cephalis, hemispherical, thorny, with a conical horn of twice the length; it is separated from the thorax by a complete internal collar septum, but without external collar stricture. Thorax flatly conical, about half as long as broad, with straight outlines; its pores subregular, hexagonal, about as large as the cephalis, with thin bars.

_Dimensions._--Cephalis 0.015 long, 0.03 broad; thorax 0.08 long, 0.18 broad.

_Habitat._--Fossil in Barbados.

5. _Sethoconus mitra_, Haeckel.

_Cornutella mitra_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. ii. fig. 8.

_Ceratocyrtis mitra_, Bütschli, 1882, Zeitschr. f. wiss. Zool., Bd.
xxxvi. p. 536.

Cephalis ovate, with slight collar stricture (not distinct enough in Ehrenberg's figure), with few large pores, and a conical stout horn of the same length. Thorax campanulate, conical, twice as long as broad, with slightly convex outlines; its pores subregular, roundish, increasing in size towards the mouth, the largest as broad as the cephalis.

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax 0.12 long, 0.07 broad.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms; fossil in Barbados.

6. _Sethoconus rayianus_, n. sp. (Pl. 58, fig. 6).

_Conarachnium rayianum_, Haeckel, 1881, Prodromus, p. 430.

Cephalis ovate, with obliterated collar stricture (but distinct internal septum), with small, irregular pores, and two to four divergent horns, which are longer than the cephalis, and two or three of which are forked. Thorax tent-shaped, conical, two-thirds as long as broad, with slightly {1292}concave outlines, and subregular, hexagonal pores, gradually increasing towards the mouth, the largest half as broad as the cephalis. This elegant species is dedicated to Dr. Ray, the discoverer of many rare Radiolarians in the Challenger collection.

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax 0.08 long, 0.12 broad.

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

7. _Sethoconus cervus_, Haeckel.

? _Eucyrtidium cervus_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 291, Taf. ix. fig. 21.

_Conarachnium cervus_, Haeckel, 1881, Prodromus, p. 430.

Cephalis subspherical, with slight collar stricture, small circular pores, and two to four divergent horns, one or two of which are forked. Thorax wide, conical, about as long as broad, with straight outlines and irregular, polygonal pores, gradually increasing towards the mouth; the largest as broad as the cephalis.

_Dimensions._--Cephalis 0.015 long, 0.02 broad; thorax 0.08 long, 0.08 broad.

_Habitat._--Indian Ocean; Maldive Islands, surface (Haeckel); Zanzibar, depth 2200 fathoms (Pullen).

8. _Sethoconus lophophæna_, n. sp.

_Conarachnium lophophæna_, Haeckel, 1881, Prodromus, p. 430.

Cephalis subspherical, with distinct collar stricture, small circular pores, and numerous (twelve to sixteen) radial, bristle-shaped horns of different lengths. Thorax wide, conical, somewhat longer than broad, with slightly convex outlines, and subregular, hexagonal pores, increasing gradually in size towards the mouth; the largest twice as broad as the cephalis.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.2 long, 0.16 broad.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

9. _Sethoconus larvatus_, Haeckel.

_Lophophæna larvata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. viii. fig. 10.

_Dictyocephalus larvatus_, Bütschli, 1882, Zeitschr. f. wiss. Zool., Bd.
xxxvi. p. 535.

Cephalis subspherical, large, with sharp collar stricture, and numerous (five to ten or more) radial, conical (partly forked) horns of different lengths. Thorax wide, conical, somewhat broader than long, with straight outlines. Pores of both joints very irregular, roundish, of very different sizes and form.

_Dimensions._--Cephalis 0.04 long, 0.05 broad; thorax 0.1 long, 0.12 broad.

_Habitat._--Fossil in Barbados.

{1293}10. _Sethoconus nassa_, Haeckel.

_Eucyrtidium nassa_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 72, Taf. ix. fig. 9.

Cephalis slenderly ovate, with sharp collar stricture, few scattered pores, and a very stout, pyramidal horn of the same length, which is surrounded at the base by three short, divergent, ascending spines (perhaps the remnants of the three cortinar rods of _Eucecryphalus_, &c. ?). Thorax slender, conical, with straight outlines, and small, dense, regular, circular pores of equal size.

_Dimensions._--Cephalis 0.04 long, 0.02 broad; thorax 0.12 long, 0.08 broad.

_Habitat._--Fossil in Barbados.

11. _Sethoconus tabulatus_, Haeckel.

_Cycladophora tabulata_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 289, Taf. iv. fig. 18.

Cephalis subspherical, with slight collar stricture, and numerous small, irregular pores, without horn, or with a small conical horn. Thorax slenderly conical, with straight outlines, and large, regular, hexagonal pores. Mouth truncate. (In the specimen I examined the thorax was longer and more conically dilated; the cephalis had a distinct small horn.)

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.08 long, 0.06 broad.

_Habitat._--North Atlantic, Antilles, depth 1600 fathoms (Ehrenberg); Station 347, depth 2250 fathoms.

Subgenus 2. _Cornutellium_ (vel _Ceratarachnium_), Haeckel, 1881, Prodromus, p. 430.

_Definition._--Cephalis very small, rudimentary, hyaline, without distinct collar septum, and without pores (or with scarce, rudimentary pores). Thorax smooth.

12. _Sethoconus hexagonalis_, Haeckel.

_Cornutella trochus_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 287, Taf. ix. fig. 14.

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the length. Thorax slenderly conical, or bottle-shaped, twice to three times as long as broad; in the lower half nearly cylindrical, with very thin, thread-like bars, and regular, hexagonal pores, increasing in size towards the mouth.

_Dimensions._--Cephalis 0.005 diameter, thorax 0.12 long, 0.05 broad.

_Habitat._--Indian Ocean, Zanzibar, depth 2200 fathoms (Pullen).

13. _Sethoconus verrucosus_, Haeckel.

_Cornutella verrucosa_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 287, Taf. ix. fig. 16.

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the {1294}length. Thorax slenderly conical, or bottle-shaped, with little convex outlines; three to four times as long as broad, papillate, with regular, circular pores, which are included by rhombic frames, and increase in size towards the mouth.

_Dimensions._--Cephalis 0.004 diameter, thorax 0.12 long, 0.035 broad.

_Habitat._--Indian Ocean (Zanzibar), depth 2200 fathoms (Pullen).

14. _Sethoconus orthoceras_, n. sp. (Pl. 54, fig. 11).

_Cornutella orthoceras_, Haeckel, 1879, Atlas, _loc. cit._

Cephalis very small, conical, hyaline, without pores, with a double internal stricture, and a very short, rudimentary horn. Thorax slenderly conical, with undulate outlines, three to four times as long as broad, with subregular, roundish pores, gradually increasing in size towards the mouth.

_Dimensions._--Cephalis 0.02 long, 0.01 broad; thorax 0.16 long, 0.04 to 0.08 broad.

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

15. _Sethoconus profundus_, Haeckel.

_Cornutella profunda_, Ehrenberg, 1854, Mikrogeol., Taf. xxxv. B, Nr. B.
iv. fig. 21.

_Cornutella profunda_, Bailey, 1856, Amer. Jour., vol. xxii. pl. i. fig.
23.

_Cornutella profunda_, Haeckel, 1862 Monogr. d. Radiol., p. 284.

Cephalis very small, spherical, hyaline without pores and internal stricture, with a very short, rudimentary horn. Thorax slenderly conical with straight outlines, three to four times as long as broad, with subregular, circular pores, gradually increasing in size towards the mouth.

_Dimensions._--Cephalis 0.004 to 0.008 diameter, thorax 0.08 to 0.12 long, 0.03 to 0.04 broad.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific; at various depths.

16. _Sethoconus trichostylus_, Haeckel.

_Cornutella trichostyla_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 287, Taf. vi. fig. 2.

Cephalis very small, conical, hyaline, without pores, with a very long, bristle-shaped, spirally twisted horn, longer than the whole shell. Thorax slenderly conical, with straight outlines, and very small, regular, circular pores of nearly equal size, which are separated by broader bars and spirally ascending oblique crests (according to the figure).

_Dimensions._--Cephalis 0.004 long, 0.002 broad; thorax 0.06 long, 0.04 broad.

_Habitat._--North Pacific (California), depth 2600 fathoms.

17. _Sethoconus longisetus_, Haeckel.

_Cornutella longiseta_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 287, Taf. ix. fig. 15.

Cephalis very small, spherical, hyaline, without pores, with a very long, bristle-shaped horn, {1295}nearly as long as the shell. Thorax slenderly conical, rough, with straight outlines, and irregular, roundish pores, gradually increasing in size towards the mouth.

_Dimensions._--Cephalis 0.01 diameter, thorax 0.09 long, 0.03 broad.

_Habitat._--Indian Ocean (Zanzibar), depth 2200 fathoms (Pullen).

18. _Sethoconus gracilis_, Haeckel.

_Eucyrtidium gracile_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf. xi. fig. 15.

Cephalis small, subspherical, with few scarce pores, and a stout, pyramidal horn, of the same length. Thorax slenderly conical, three to four times as long as broad, with straight outlines, and very small and numerous circular pores of equal size.

_Dimensions._--Cephalis 0.015 diameter, thorax 0.12 long, 0.04 broad.

_Habitat._--Fossil in Barbados.

19. _Sethoconus bimarginatus_, n. sp. (Pl. 54, fig. 12).

_Cornutella bimarginata_, Haeckel, 1879, Atlas, _loc. cit._

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary, conical horn of the same length. Thorax slenderly conical, three times as long as broad, with undulated, little convex outlines, and irregular, roundish, double-contoured pores, arranged in nine longitudinal series, markedly increasing in size towards the mouth.

_Dimensions._--Cephalis 0.01 diameter, thorax 0.16 long, 0.05 broad.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

20. _Sethoconus clathratus_, Haeckel.

_Cornutella clathrata_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig.
39_a_, _b_, _c_.

Cephalis very small, subspherical, hyaline, without pores, with a rudimentary horn of half the length. Thorax slenderly conical, three to four times as long as broad, smooth, with curved axis and small, regular, circular pores, nearly equal in size. This common species differs from all others of the genus by the curvation of the axis of the shell, which is more or less crescentic, or curved like a cowherd's horn; it may, therefore, represent a peculiar genus, _Sethodrepanum_.

_Dimensions._--Cephalis 0.003 to 0.006 diameter, thorax 0.08 to 0.16 long, 0.03 to 0.05 broad.

_Habitat._--Cosmopolitan; Atlantic, Pacific, many stations; fossil in Barbados and Sicily.

Subgenus 3. _Phlebarachnium_, Haeckel (et _Cladarachnium_, Haeckel), 1881, Prodromus, p. 430.

_Definition._--Cephalis small, with very small pores, and internal collar septum. Thorax spiny or thorny.

{1296}21. _Sethoconus facetus_, n. sp. (Pl. 55, fig. 1).

_Phlebarachnium facetum_, Haeckel, 1881, Prodromus, p. 430.

Cephalis small, hemispherical, with distinct collar septum, the same network as the thorax, and numerous bristle-shaped horns of the same length. Thorax wide, conical, about as long as broad, with slightly convex outlines; its network extremity delicate, with very small and numerous, regular, hexagonal pores, disposed in numerous divergent, longitudinal series, which are convoluted somewhat spirally around the shell axis. Surface covered with thin, scattered, bristle-shaped spines, about as long as the cephalis.

_Dimensions._--Cephalis 0.02 diameter, thorax 0.2 long, 0.22 broad.

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

22. _Sethoconus anthocyrtis_, n. sp. (Pl. 62, fig. 21).

_Anthocyrtis sethoconus_, Haeckel, 1879, Atlas, _loc. cit._

Cephalis small, subspherical, with very small pores and numerous radial, bristle-shaped spines of the same length. Thorax wide, conical, about as long as broad, with parabolic outlines, its network very delicate, with subregular, hexagonal meshes. Surface with scarce, bristle-shaped spines (not represented in the figure). Mouth with a corona of numerous small, vertical spines.

_Dimensions._--Cephalis 0.025 diameter, thorax 0.26 long, 0.24 broad.

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

23. _Sethoconus virgultus_, n. sp.

_Cladarachnium virgultum_, Haeckel, 1881, Prodromus, p. 430.

Cephalis and thorax nearly of the same form and stricture as in _Sethoconus facetus_, but larger and wider, with the same delicate, hexagonal network (Pl. 55, fig. 1); it differs from the latter by the wider, more convex and campanulate form, but mainly by the armature of the surface, which is densely covered with thin, arborescent, bristle-shaped spines, irregularly branched, and four to eight times as large as the cephalis.

_Dimensions._--Cephalis 0.02 diameter, thorax 0.32 long, 0.4 broad.

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

24. _Sethoconus setosus_, n. sp.

_Phlebarachnium setosum_, Haeckel, 1881, Prodromus, p. 430.

Cephalis small, subspherical, with distinct collar septum, and the same network as the thorax, with numerous bristle-shaped horns of the same length. Thorax slenderly conical, twice as long as broad, with irregular, polygonal pores of little different sizes, and very thin bars. Surface covered with perpendicular, simple, bristle-shaped spines, about as long as the cephalis.

_Dimensions._--Cephalis 0.02 diameter, thorax 0.12 long, 0.22 broad.

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

{1297}25. _Sethoconus venosus_, n. sp. (Pl. 55, fig. 2).

_Phlebarachnium venosum_, Haeckel, 1881, Prodromus, p. 430, et Atlas,
_loc. cit._

Cephalis subspherical, with a stout prismatic horn twice the length, bearing three denticulate edges. The uppermost part of the thorax is supported by three diverging, radial beams arising from the deep collar stricture. Thorax wide, conical, nearly twice as long as broad, with slightly convex, thorny outlines; its delicate network is composed of very irregular, polygonal meshes of different sizes, separated by stronger bars, and of numerous very small polygonal pores separated by very thin bars inside the former. The central capsule of the figured specimen exhibited in the upper third of the thorax four large club-shaped lobes, which arose from a very small sphere enclosed in the cephalis and containing the nucleus.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.4 long, 0.3 broad.

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

Genus 573. _Periarachnium_,[190] Haeckel, 1881, Prodromus, p. 430.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with conical or campanulate, gradually dilated thorax, and widely open mouth. Primary lattice-shell enveloped by an external arachnoidal mantle. Cephalis with one or more horns.

The genus _Periarachnium_ has been derived from those forms of the preceding _Sethoconus_, in which the conical thorax is covered with simple spines (_Phlebarachnium_) or branched spines (_Cladarachnium_). By communication of the branches of these spines a second outer shell is formed, which, like an arachnoidal mantle, envelops the inner primary shell.

1. _Periarachnium periplectum_, n. sp. (Pl. 55, fig. 11).

Cephalis hemispherical, separated from the thorax by a sharp collar stricture, from which arise three internal, diverging beams supporting its upper third. Thorax campanulate, conical, about as long as broad, with slightly convex outlines. The delicate lattice-work of the entire shell is double; the inner composed of subregular, hexagonal meshes; the outer of larger, irregular, polygonal meshes. The bars of the inner are much thicker than the thin threads of the outer. Both shells are connected by numerous bristle-shaped beams. The central capsule of the figured specimen exhibited in the upper part of the thorax three club-shaped lobes, which arose from a sphere enclosed in the cephalis and containing the nucleus.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.15 long, 0.12 broad.

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

{1298}Genus 574. _Sethocephalus_,[191] Haeckel, 1881, Prodromus, p. 430.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with discoidal, flatly expanded thorax. Cephalis large, without horn.

The genus _Sethocephalus_ (formerly proposed under the name _Platycryphalus_) contains some few and rare Sethocorida, distinguished by the very large cephalis, the collar opening of which is wide open, not closed by cortinar beams, and surrounded by a very flat, nearly discoidal thorax, like the brim of a hat. It is possible that this peculiar genus has been derived from a Tricyrtid (_Theocalyptra_?) by loss of the original cephalis, and that the apparent large cephalis is the original thorax.

1. _Sethocephalus eucecryphalus_, n. sp. (Pl. 56, fig. 13).

Cephalis very large, campanulate-conical, with irregular, polygonal pores and thin bars. Thorax short, scarcely broader than the cephalis, beyond the sharp collar stricture expanded like the brim of a hat, with few rows of irregular, polygonal pores. (In the specimen figured the thorax was only half as broad as in another specimen found afterwards.)

_Dimensions._--Cephalis 0.12 long, 0.09 broad; thorax 0.02 long, 0.12 broad.

_Habitat._--South Pacific, Station 285, surface.

2. _Sethocephalus platycryphalus_, n. sp.

_Platycryphalus sethodiscus_, Haeckel, 1881, Prodromus, p. 430.

Cephalis large, hemispherical, with irregular square pores and thin bars. Thorax flatly conical, three to four times as broad as the cephalis, beyond the collar stricture expanded nearly discoidally, with a delicate network of small, subregular, hexagonal pores. (Similar in general form to _Sethophormis aurelia_, Pl. 55, fig. 3, but without any trace of collar beams or radial ribs.)

_Dimensions._--Cephalis 0.04 long, 0.08 broad; thorax 0.04 long, 0.3 broad.

_Habitat._--South Pacific, Station 289, surface.

Genus 575. _Sethocyrtis_,[192] n. gen.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with ovate or subcylindrical thorax, the mouth of which is constricted, simple, without prominent hyaline peristome. Cephalis with an apical horn.

{1299}The genus _Sethocyrtis_ and the three following nearly allied genera differ from the three preceding genera of Sethocorida in the form of the thorax, which is not gradually dilated, conical, but cylindrical or ovate, with more or less constricted mouth. _Sethocyrtis_ may be derived from _Anthocyrtis_ by loss of the terminal feet. Its mouth is quite simple, without tubular or annular peristome.

1. _Sethocyrtis oxycephalis_, n. sp. (Pl. 62, fig. 9).

Shell rough, subconical, with slight collar stricture. Length of the two joints = 4 : 9, breadth = 3 : 8. Cephalis ovate, with a pyramidal horn of half the length. Thorax campanulate, with regular, circular pores, twice as broad as those of the cephalis. Mouth constricted, scarcely half as broad as the thorax.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax 0.09 long, 0.08 broad.

_Habitat._--Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.

2. _Sethocyrtis cancrina_, Haeckel.

_Eucyrtidium cancrinum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf. x. fig. 4.

Shell smooth, bottle-shaped, with obliterated collar stricture. Length of the two joints = 4 : 9, breadth = 2 : 7. Cephalis subcylindrical, with a stout conical horn of the same length, and sometimes a smaller accessory horn at its base. Thorax ovate, truncate, with regular, circular, quincuncial pores, twice as broad as those of the cephalis. Mouth little constricted, flat, nearly as broad as the thorax.

_Dimensions._--Cephalis 0.04 long, 0.02 broad; thorax 0.09 long, 0.07 broad.

_Habitat._--Fossil in Barbados.

3. _Sethocyrtis diomedis_, n. sp.

Shell thorny, pear-shaped, with slight collar stricture. Length of the two joints = 3 : 16, breadth = 4 : 20. Cephalis hemispherical, with a conical horn of twice the length. Thorax inflate, ovate, truncate at both poles, with regular, circular pores, twice as broad as those of the thorax. Mouth constricted, flat, half as broad as the thorax.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.12 to 0.16 long, 0.16 to 0.2 broad.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms; also fossil in Barbados.

4. _Sethocyrtis menelai_, n. sp.

Shell spiny, pear-shaped, with sharp collar stricture. Length of the two joints = 3 : 15, breadth = 4 : 18. Cephalis subspherical, with a large, cylindro-conical horn, about as long as the whole shell. {1300}Thorax inflate, subspherical, truncate, with large, irregular, roundish pores, four to six times as large as those of the cephalis. Mouth constricted, flat, one-third as broad as the thorax.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.15 long, 0.18 broad.

_Habitat._--Fossil in Barbados.

5. _Sethocyrtis subacuta_, Haeckel.

_Eucyrtidium subacutum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 293, Taf. vii. fig. 18.

Shell smooth, pear-shaped, with sharp collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 3. Cephalis subspherical, with small, irregular pores and a rudimentary horn of half the length. Thorax ovate, with large, subregular, hexagonal pores and thin bars between them. Mouth constricted, flat, half as broad as the thorax, without prominent peristome.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.08 long, 0.06 broad.

_Habitat._--Philippine Sea, depth 3300 fathoms (Ehrenberg).

6. _Sethocyrtis pleuracantha_, Haeckel.

_Eucyrtidium pleuracanthum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 293, Taf. vii. fig. 21.

Shell smooth, bottle-shaped, with distinct collar stricture. Length of the two joints = 2 : 4, breadth = 1 : 3. Cephalis slenderly ovate, with an excentric pyramidal horn of the same length. Thorax inflate, ovate, with irregular, roundish pores and thin bars between them. Mouth constricted, flat, half as broad as the thorax, without prominent peristome.

_Dimensions._--Cephalis 0.04 long, 0.02 broad; thorax 0.08 long, 0.06 broad.

_Habitat._--Tropical Pacific, Stations 200, 225, 266, 274, &c., at various depths.

7. _Sethocyrtis agamemnonis_, n. sp. (Pl. 62, figs. 11, _a_, _b_).

Shell pear-shaped, rough, with sharp collar stricture. Length of the two joints = 2 : 10, breadth = 3 : 8. Cephalis subspherical, with very small pores and a small, pyramidal horn of half the length. Thorax inflate, ovate; in the uppermost part (beyond the collar stricture) with a ring of six to nine very large roundish pores, which are twice to four times as broad as the other irregular, roundish pores. (The shell is seen in fig. 11 from the apical pole, in fig. 11_a_ with the cephalis, in fig. 11_b_ without it, exhibiting the four central collar pores of the cortinar septum.) Mouth truncate, without prominent peristome.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.1 long, 0.08 broad.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

{1301}8. _Sethocyrtis cassis_, Haeckel.

_Cornutella cassis_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 38.

_Cyrtocalpis cassis_, Haeckel, 1862, Monogr. d. Radiol., p. 287.

Shell pear-shaped, smooth, with obliterated collar stricture. Length of the two joints = 4 : 13, breadth = 3 : 12. Cephalis ovate, with a conical horn of half the length. Thorax inflate, ovate, with subregular, circular, quincuncial pores, twice to three times as broad as the bars. Mouth constricted, truncate, two-thirds as broad as the thorax, without prominent peristome.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax 0.13 long, 0.12 broad.

_Habitat._--Fossil in Tertiary rocks of Sicily (Caltanisetta).

Genus 576. _Sethocorys_,[193] Haeckel, 1881, Prodromus, p. 430.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with ovate or sub-cylindrical thorax, the mouth of which is constricted and prolonged into a ring-like peristome. Cephalis with an apical horn.

The genus _Sethocorys_ differs from the preceding _Sethocyrtis_, its ancestral form, in the form of the constricted mouth, which is prolonged into a prominent, hyaline, tubular, or annular peristome.

1. _Sethocorys achillis_, n. sp. (Pl. 62, fig. 8).

Shell rough, pear-shaped, with distinct collar stricture. Length of the two joints = 4 : 8, breadth = 3 : 8. Cephalis ovate, with a stout pyramidal horn of half the length. Thorax nearly spherical, with regular, circular, quincuncial pores of the same breadth as the cephalic pores. Mouth constricted, half as broad as the thorax, with a broad, smooth, striated peristome.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax 0.08 long, 0.08 broad.

_Habitat._--Cosmopolitan; Mediterranean (Corfu), Atlantic, Indian, Pacific; many stations, at various depths.

2. _Sethocorys patrocli_, n. sp.

Shell thorny, pear-shaped, with slight collar stricture. Length of the two joints = 4 : 12, breadth = 3 : 10. Cephalis ovate, with a pyramidal horn of twice the length. Thorax ovate, truncate at both poles, with regular, circular pores, twice as broad as the cephalic pores. Mouth constricted, half as broad as the thorax, with a broad, smooth, prominent peristome.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax 0.12 long, 0.1 broad.

_Habitat._--Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.

{1302}3. _Sethocorys armadillo_, Haeckel.

_Eucyrtidium armadillo_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf ix. fig. 10.

Shell slenderly ovate, smooth, with deep collar stricture. Length of the two joints = 3 : 10, breadth = 4 : 6. Cephalis ovate, at the apex thorny, with a conical horn of the same length. Thorax smooth, ovate, truncate, with small, regular, circular pores, disposed in from twelve to fifteen transverse rows of the same breadth as the cephalic pores. Mouth constricted, half as broad as the thorax, with a broad, hyaline, prominent peristome.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.1 long, 0.06 broad.

_Habitat._--Fossil in Barbados.

4. _Sethocorys odysseus_, n. sp. (Pl. 62, fig. 10).

Shell ovate, smooth, with obliterated collar stricture. Length of the two joints = 2 : 9, breadth = 4 : 8. Cephalis hemispherical, with a slender, conical horn of the same length. Thorax nearly spherical, with regular, circular pores, of the same breadth as the cephalic pores, quincuncially disposed. Mouth constricted, only one-third as broad as the thorax, with a broad, hyaline, prominent peristome.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.09 long, 0.08 broad.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

5. _Sethocorys amphora_, Haeckel.

_Lophophæna amphora_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 99, Taf.
iii. fig. 11.

Shell ovate, mouth with distinct collar stricture. Length of the two joints = 1 : 5, breadth = 2 : 4. Cephalis hemispherical, with a short conical horn of half the length. Thorax ovate, truncate, with small, regular, circular, quincuncial pores. Mouth constricted, half as broad as the thorax, with a narrow, prominent, hyaline peristome.

_Dimensions._--Cephalis 0.015 long, 0.03 broad; thorax 0.07 long, 0.06 broad.

_Habitat._--Fossil in Tertiary rocks of Sicily; Grotte (Stöhr).

6. _Sethocorys ajacis_, n. sp.

Shell slenderly ovate, smooth, without external collar stricture, but with an internal septum. Length of the two joints = 1 : 3, breadth = 1 : 2. Cephalis conical, with a large pyramidal horn of twice the length, and sometimes with a smaller accessory horn at its base; its pores scarce, irregular. Thorax ovate, truncate, hyaline, in the greater part without pores, in the smaller part {1303}with from two to four transverse rows of small, circular pores only. Mouth constricted, with a large cylindrical, tubular, hyaline peristome, half as long as the shell.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.09 long, 0.07 broad.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Genus 577. _Lophophæna_,[194] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with ovate or subcylindrical thorax, the mouth of which is either truncate or constricted. Cephalis armed with several large horns.

The genus _Lophophæna_ differs from the nearly allied _Sethocorys_ and _Dictyocephalus_ only in the armature of the large cephalis, which bears a group of large horns, often arranged in a corona of radial spines. Sometimes these spines are connected by anastomosing branches (like _Arachnocorys_).

Subgenus 1. _Lophophænula_, Haeckel.

_Definition._--Horns of the cephalis simple, free, radial spines, neither branched nor connected.

1. _Lophophæna galea_, Ehrenberg.

_Lophophæna galea orci_, Ehrenberg, 1854, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin p. 245.

_Lophophæna apiculata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. viii. fig. 11.

? _Cornutella spiniceps_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. ii. fig. 6.

Shell with slight collar stricture. Length of the two joints = 5 : 4, breadth = 5 : 6. Cephalis subglobular, with numerous bristle-shaped, radial spines, about as long as its radius. Thorax about the same size, truncate, conical, smooth, with wide open mouth. Pores in both joints of equal size, small, regular, circular.

_Dimensions._--Cephalis 0.05 long, 0.05 broad; thorax 0.04 long, 0.06 broad.

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms; also fossil in Barbados.

3. _Lophophæna radians_, Ehrenberg.

_Lophophæna radians_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. viii. fig. 9.

? _Lophophæna lynx_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. viii. fig. 13.

Shell with slight collar stricture. Length of the two joints = 4 : 6, breadth = 4 : 5. Cephalis subglobular, with numerous, stout, conical, radial spines, about as long as its diameter. Thorax {1304}of about the same size, subcylindrical, smooth, truncate, with wide open mouth. Pores in both joints of equal size, small, regular, circular.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.06 long, 0.05 broad.

_Habitat._--Cosmopolitan; Atlantic, Indian, Pacific; also fossil in Barbados.

3. _Lophophæna liothorax_, n. sp.

Shell with distinct collar stricture. Length of the two joints = 4 : 10, breadth = 4 : 8. Cephalis subglobular, with large, circular, hexagonally-framed pores, and with numerous stout, conical, radial spines, about as long as its diameter. Thorax twice as long, ovate, smooth, truncate, with little constricted mouth, and with irregular, roundish pores, of very different sizes.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.1 long, 0.08 broad.

_Habitat._--Central Pacific, Stations 270 to 274, depth 2350 to 2925 fathoms.

4. _Lophophæna echinocephala_, n. sp.

Shell with deep collar stricture. Length of the two joints = 4 : 8, breadth = 4 : 9. Cephalis subglobular, of the same shape as in the preceding species. Thorax thorny, inflate, nearly spherical, with a constricted mouth of half the breadth, and with irregular, roundish, double-contoured pores.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.08 long, 0.09 broad.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Subgenus 2. _Lophophænoma_, Haeckel.

_Definition._--Horns of the cephalis connected by anastomosing branches.

5. _Lophophæna circumtexta_, Haeckel.

_Lophophæna radians_, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 78, Taf. viii. figs. 7, 8.

Shell with slight collar stricture. Length of the two joints = 4 : 5, breadth = 4 : 5. Cephalis subglobular, with numerous conical, radial spines, about as long as its diameter, and at equal distances from the surface, connected by anastomosing branches. Thorax nearly cylindrical, smooth, little dilated towards the truncate, wide open mouth. Pores subregular, circular.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.05 long, 0.05 broad.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms; also fossil in Barbados.

{1305}Genus 578. _Dictyocephalus_,[195] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 830.

_Definition._--#Sethocorida# (vel Dicyrtida eradiata aperta) with ovate or subcylindrical thorax, the mouth of which is more or less constricted, either truncate or with a ring-like peristome. Cephalis rounded, without horn.

The genus _Dictyocephalus_ has originated probably from _Sethocorys_ by reduction and loss of the apical horn. The mouth is more or less constricted, either simple, truncate (_Dictyocryphalus_), or provided with a prominent, broad, hyaline, annular peristome (_Dictyoprora_).

Subgenus 1. _Dictyoprora_, Haeckel, 1881, Prodromus, p. 430.

_Definition._--Mouth of the thorax constricted, with a prominent, ring-like or tubular, hyaline peristome.

1. _Dictyocephalus amphora_, n. sp. (Pl. 62, fig. 4).

Shell smooth, thick-walled, subovate, with slight collar stricture. Length of the two joints = 5 : 9, breadth = 6 : 8. Cephalis large, obtusely conical, with numerous oblique pore-canals. Thorax inflate, with six to eight transverse rows of roundish pores, increasing in size towards the base. Mouth constricted, one-third as broad as the thorax, with an internal diaphragm and a narrow hyaline peristome.

_Dimensions._--Cephalis 0.05 long, 0.06 broad; thorax 0.09 long, 0.08 broad.

_Habitat._--Central Pacific, Stations 265 to 272, depth 2425 to 2925 fathoms.

2. _Dictyocephalus urceolus_, n. sp.

? _Eucyrtidium Mongolfieri_, Bury, 1862, Polycystins of Barbados, pl. v.
fig. 2.

Shell smooth, thick-walled, urceolate, with obliterated collar stricture. Length of the two joints = 5 : 12, breadth = 4 : 10. Cephalis campanulate, with numerous oblique pore-canals. Thorax inflate, with five or six transverse rows of roundish pores of equal size. Mouth constricted, nearly half as broad as the thorax, with a broad hyaline peristome.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.12 long, 0.1 broad.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms; also fossil in Barbados.

{1306}3. _Dictyocephalus excellens_, Haeckel.

_Eucyrtidium excellens_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf. x. fig. 2.

Shell annulate, thick-walled, urceolate, with slight collar stricture. Length of the two joints = 5 : 10, breadth = 4 : 7. Cephalis large, ovate-conical, with numerous oblique pore-canals. Thorax ovate, with ten to twelve transverse rows of regular, roundish pores, which are separated by prominent annular ribs. Mouth constricted, about half as broad as the thorax, with a broad hyaline peristome.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.1 long, 0.07 broad.

_Habitat._--Fossil in Barbados.

4. _Dictyocephalus ocellatus_, Haeckel.

_Dictyocephalus ocellatus_, Haeckel, 1862, Monogr. d. Radiol., p. 297.

? _Eucyrtidium ocellatum_, Ehrenberg, 1861, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 299.

Shell smooth, thick-walled, with deep collar stricture. Length of the two joints = 3 : 9, breadth = 4 : 7. Cephalis subspherical, with numerous oblique pore-canals. Thorax inflate, campanulate, hyaline, only with three or four remote transverse rows of circular, double-contoured pores of equal size. Mouth constricted, one-third as broad as the thorax, with a narrow hyaline annular peristome.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.09 long, 0.07 broad.

_Habitat._--North Atlantic, Greenland; Færöe Channel (Gulf Stream), John Murray.

5. _Dictyocephalus crassiceps_, Haeckel.

_Eucyrtidium crassiceps_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf. xi. fig. 4.

Shell smooth, thick-walled, with sharp collar stricture. Length of the two joints = 4 : 6, breadth = 3 : 4. Cephalis ovate, in the upper part with scattered pores, in the lower part with one transverse row of pores. Thorax hyaline, subcylindrical, only with four or five remote transverse rows of small, circular pores. Mouth constricted, half as broad as the thorax, with a short hyaline peristome.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax 0.06 long, 0.04 broad.

_Habitat._--Fossil in Barbados.

6. _Dictyocephalus australis_, n. sp. (Pl. 62, fig. 1).

Shell smooth, thick-walled, with slight collar stricture. Length of the two joints = 2 : 9, breadth = 3 : 6. Cephalis hemispherical, with few small pores. Thorax subcylindrical, with large, {1307}roundish, double-contoured pores, irregularly disposed. Mouth constricted, two-thirds as broad as the thorax, with a broad, hyaline peristome.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.09 long, 0.06 broad.

_Habitat._--East coast of Australia, Station 164, surface.

7. _Dictyocephalus mediterraneus_, n. sp. (Pl. 62, fig. 2).

Shell rough, thin-walled, with slight collar stricture. Length of the two joints = 3 : 10, breadth = 4 : 8. Cephalis hemispherical, with small, circular pores. Thorax ovate, truncate, with much larger circular pores of different sizes and thin bars between them. Mouth little constricted, two-thirds as broad as the thorax, with a narrow, hyaline peristome.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.1 long, 0.08 broad.

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

8. _Dictyocephalus papillosus_, Haeckel.

_Eucyrtidium papillosum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 293, Taf. vii. fig. 10.

Shell thin-walled, papillate, with obliterated collar stricture. Length of the two joints = 2 : 7, breadth = 3 : 5. Cephalis hemispherical, with small, circular pores. Thorax slenderly ovate, with larger, subregular, circular pores, separated by oblique series of conical papillæ. Mouth with a broad, hyaline peristome (the "third articulus" of Ehrenberg), separated by a stricture from the little broader thorax.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.07 long, 0.05 broad.

_Habitat._--Western Tropical Pacific (Philippine Sea), depth 3300 fathoms.

9. _Dictyocephalus tabulatus_, n. sp.

Shell thin-walled, papillate, with obliterated collar stricture. Length of the two joints = 2 : 10, breadth = 3 : 7. Cephalis hemispherical, with small, circular pores. Thorax slenderly ovate, truncate, with large, subregular, circular, hexagonally-framed pores. Mouth little constricted, nearly as broad as the thorax, with a broad, hyaline peristome.

_Dimensions._--Cephalis 0.02 long, 0.03 broad, thorax 0.1 long, 0.07 broad.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

10. _Dictyocephalus reticulum_, Haeckel.

_Dictyocephalus reticulum_, Haeckel, 1862, Monogr. d. Radiol., p. 297.

_Eucyrtidium reticulum_, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 300.

Shell thin-walled, smooth, with deep collar stricture. Length of the two joints = 2 : 8, breadth = 3 : 5. Cephalis subspherical, with small, circular pores. Thorax campanulate, with {1308}transverse rows of alternating square pores. Mouth little constricted, nearly as long as the thorax, with a narrow, prominent peristome.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.08 long, 0.05 broad.

_Habitat._--Arctic Ocean, Greenland (Schaffner); Iceland (Krabbe).

11. _Dictyocephalus ampulla_, n. sp.

Shell thin-walled, smooth, with slight collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 3. Cephalis subspherical, without pores, hyaline. Thorax inflate, subspherical, with scarce and small, widely-scattered, circular pores. Mouth constricted, only one-third as broad as the thorax, with a narrow, prominent peristome.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.08 long, 0.07 broad.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. _Dictyocryphalus_, Haeckel, 1881, Prodromus, p. 430.

_Definition._--Mouth of the thorax flat or truncate, without prominent ring-like peristome.

12. _Dictyocephalus obtusus_, Ehrenberg.

_Dictyocephalus obtusus_, Ehrenberg, 1860, Monatsber. d. k. preuss. Akad.
d. Wiss. Berlin, p. 830.

_Lophophæna obtusa_, Ehrenberg, 1854, Mikrogeol., Taf. xxii. fig. 40.

_Cornutella obtusa_, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 877.

_Dictyocephalus obtusus_, Haeckel, 1862, Monogr. d. Radiol., p. 296.

Shell smooth, thick-walled, with distinct collar stricture. Length of the two joints = 5 : 6, breadth = 4 : 5. Cephalis ovate, little smaller than the subcylindrical thorax. Pores subregular, circular, of little different sizes. Mouth truncate, without ring-like peristome.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.06 long, 0.05 broad.

_Habitat._--Fossil in Tertiary rocks of Sicily (Caltanisetta), Grotte, &c.

13. _Dictyocephalus globiceps_, n. sp. (Pl. 62, fig. 7).

Shell rough, thin-walled, with distinct collar stricture. Length of the two joints = 6 : 8, breadth = 6 : 7. Cephalis subspherical, large, with circular, double-contoured pores. Thorax cylindrical, with irregular, roundish pores, the size of which, like the thickness of the wall, decreases gradually towards the truncate mouth, which has no ring-like peristome.

_Dimensions._--Cephalis 0.06 long, 0.06 broad; thorax 0.08 long, 0.07 broad.

_Habitat._--Central Pacific, Station 271, depth 2425 fathoms.

{1309}14. _Dictyocephalus cavea_, n. sp.

Shell rough, thin-walled, with slight collar stricture. Length of the two joints = 3 : 10, breadth = 5 : 7. Cephalis hemispherical, thorny, with numerous regular, circular pores. Thorax subcylindrical, with very large, circular, hexagonally-framed pores (in nine longitudinal alternating rows), three to five times as broad as the cephalic pores. Mouth truncate, wide open, without ring-like peristome.

_Dimensions._--Cephalis 0.06 long, 0.1 broad; thorax 0.2 long, 0.14 broad.

_Habitat._--Central Pacific, Station 266, depth 2750 fathoms.

15. _Dictyocephalus capito_, Ehrenberg.

_Dictyocephalus capito_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 289, Taf. vii. fig. 24.

Shell smooth, thin-walled, with sharp collar stricture. Length of the two joints = 7 : 9, breadth = 6 : 8. Cephalis ovate, with numerous irregular, roundish, densely-crowded pores. Thorax ovate, with very few widely-scattered, irregular, roundish pores (broken off in Ehrenberg's figure). Mouth truncate, little constricted, without ring-like peristome.

_Dimensions._--Cephalis 0.07 long, 0.06 broad; thorax 0.09 long, 0.08 broad.

_Habitat._--Western Tropical Pacific (Philippine Sea) Station 206, depth 2100 fathoms.

16. _Dictyocephalus hispidus_, Ehrenberg.

_Dictyocephalus hispidus_, Ehrenberg, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin; Abhandl. d. k. Akad. d. Wiss. Berlin, 1872, p. 289, Taf. v.
fig. 18.

Shell rough, thin-walled, with deep collar stricture. Length of the two joints = 3 : 4, breadth = 3 : 5. Cephalis subspherical, spiny, with the same irregular, roundish pores as the funnel-shaped or nearly ovate thorax. Mouth truncate, little narrower than the thorax, without ring-like peristome.

_Dimensions._--Cephalis 0.03 long, 0.03 broad; thorax 0.04 long, 0.05 broad.

_Habitat._--Tropical Atlantic, Mexican Gulf (Ehrenberg); Station 338, depth 1990 fathoms.

Subfamily 2. SETHOCAPSIDA, Haeckel, 1881, Prodromus, p. 433.

_Definition._--#Sethocyrtida# with the basal mouth of the shell fenestrated (vel Dicyrtida eradiata clausa).

{1310}Genus 579. _Sethocapsa_,[196] Haeckel, 1881, Prodromus, p. 433 (sensu emendato).

_Definition._--#Sethocapsida# (vel Dicyrtida eradiata clausa) with a free cephalis bearing an apical horn.

The genus _Sethocapsa_ and the two following genera represent together the small subfamily of Sethocapsida, or those Dicyrtida in which the mouth of the thorax is closed, and no radial apophyses are present. _Sethocapsa_ may be derived either from _Lithopera_ by loss of the three radial rods, or from _Sethocyrtis_ by closure of the mouth.

1. _Sethocapsa pyriformis_, n. sp. (Pl. 57, fig. 2).

Shell rough, pear-shaped, with slight collar stricture. Length of the two joints = 3 : 10, breadth = 3 : 8. Cephalis subspherical, with numerous small pores, and a short pyramidal or conical horn of half the length. Thorax ovate, with subregular, circular, quincuncial pores.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.1 long, 0.08 broad.

_Habitat._--Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.

2. _Sethocapsa lagena_, Haeckel.

_Lithopera lagena_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. iii. fig. 4.

Shell smooth, pear-shaped, with sharp collar stricture. Length of the two joints = 3 : 8, breadth = 3 : 6. Cephalis pear-shaped, with few scarce pores, and a small conical horn of half the length. Thorax pear-shaped, with irregular, roundish pores. This species differs from the similar _Lithopera lagena_ almost only in the complete absence of the three internal radial collar beams inside the thorax, and may be derived from it by their retrograde metamorphosis.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.08 long, 0.06 broad.

_Habitat._--Fossil in Barbados.

3. _Sethocapsa macroceros_, n. sp.

Shell smooth, pear-shaped, with slight collar stricture. Length of the two joints = 2 : 11, breadth = 2 : 9. Cephalis subspherical, with small circular pores, and a very large, straight, pyramidal horn, of about the same length as the shell. Thorax ovate, with large, irregular, roundish pores, which are surrounded by polygonal frames.

_Dimensions._--Cephalis 0.02 diameter, thorax 0.11 long, 0.09 broad.

_Habitat._--Central Pacific, Station 270, depth 2925 fathoms.

{1311}4. _Sethocapsa nidus_, Haeckel.

_Lithopera nidus pendulus_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 78, Taf. iii. fig. 7.

Shell smooth, pear-shaped, with distinct collar stricture. Length of the two joints = 3 : 6, breadth = 3 : 5. Cephalis subspherical, with a large, straight, pyramidal horn of twice the length, and scarce small pores. Thorax ovate, also with very small and scarce pores.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.06 long, 0.05 broad.

_Habitat._--Fossil in Barbados.

5. _Sethocapsa bulla_, n. sp.

Shell spiny, with slight collar stricture. Length of the two joints = 3 : 12, breadth = 4 : 12. Cephalis hemispherical, with small, scarce pores, and a conical horn of the same length. Thorax nearly spherical, with large, subregular, circular, quincuncial pores, twice as broad as the bars.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.12 long, 0.12 broad.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms; fossil in Barbados.

6. _Sethocapsa ampulla_, n. sp.

Shell papillate, with slight collar stricture. Length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis hemispherical, hyaline, without pores, with a large pyramidal horn of twice the length. Thorax nearly spherical, with large, irregular, roundish, lobulated pores.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.15 long, 0.15 broad.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

7. _Sethocapsa staurocephala_, Haeckel.

? _Lithopera oxystauros_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. iii. fig. 6.

? _Lithopera amblystauros_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 78, Taf. iii. fig. 5.

Shell smooth, with slight collar stricture. Length of the two joints = 3 : 4, breadth = 3 : 4. Cephalis large, ovate, with a conical horn of the same length, small scarce pores, and an internal frontal septum, composed of two crossed beams, a vertical and a horizontal. Thorax little larger than the cephalis, ovate, with irregular, small and scarce pores. (The two figures of Ehrenberg are either incomplete--in _Lithopera amblystauros_, the cephalic horn, and in _Lithopera oxystauros_, the basal part of the thorax, being broken off--or they belong to different #Botryodea#).

_Dimensions._--Cephalis 0.03 diameter, thorax 0.04 diameter.

_Habitat._--Fossil in Barbados.

{1312}Genus 580. _Dicolocapsa_,[197] Haeckel, 1881, Prodromus, p. 433 (sensu emendato).

_Definition._--#Sethocapsida# (vel Dicyrtida eradiata clausa) with a free cephalis, without apical horn.

The genus _Dicolocapsa_ differs from the preceding _Sethocapsa_ in the loss of the apical horn, and therefore bears to it the same relation that _Dictyocephalus_ does to _Sethocyrtis_.

1. _Dicolocapsa microcephala_, n. sp. (Pl. 57, fig. 1).

Shell smooth, thin-walled, with distinct collar stricture. Cephalis small, subspherical, with small, crowded pores. Length of the two joints = 1 : 3, breadth = 1 : 3. Thorax also nearly spherical, three times as large as the cephalis, with small, irregularly scattered, circular pores, and much broader bars.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.09 diameter.

_Habitat._--Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. _Dicolocapsa megacephala_, n. sp.

Shell smooth, thin-walled, with sharp collar stricture. Cephalis large, conical, obtuse. Length of the two joints = 5 : 9, breadth = 6 : 8. Thorax ovate, truncate, with hemispherical base. Pores of both joints equal, subregular, circular, about as broad as the bars.

_Dimensions._--Cephalis 0.05 long, 0.06 broad; thorax 0.09 long, 0.08 broad.

_Habitat._--Central Pacific, Station 272, depth 2600 fathoms.

3. _Dicolocapsa platycephala_, n. sp.

Shell papillate, thick-walled, with slight collar stricture. Cephalis flat, hemispherical, hyaline, without pores (or with few small pores). Length of the two joints = 2 : 11, breadth = 4 : 9. Thorax ovate, with small, regular, circular pores, half as broad as the bars.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.11 long, 0.09 broad.

_Habitat._--Fossil in Barbados.

Genus 581. _Cryptocapsa_,[198] Haeckel, 1881, Prodromus, p. 433.

_Definition._--#Sethocapsida# (vel Dicyrtida eradiata clausa) with a cephalis hidden in the thorax, without apical horn.

{1313}The genus _Cryptocapsa_ differs from the preceding _Dicolocapsa_, its ancestral form, in the peculiar shape of the cephalis, which is nearly perfectly enclosed in the upper part of the inflated thorax. It has, therefore, to the latter the same relation as _Carpocanium_ bears to _Anthocyrtis_.

1. _Cryptocapsa bacca_, n. sp.

Cephalis spherical, with small circular pores enclosed in the upper part of the thorax, which is ovate, smooth, and exhibits regular, circular pores, about as broad as the bars.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.15 long, 0.12 broad.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms.

2. _Cryptocapsa pila_, n. sp.

Cephalis spherical, with few small pores, enclosed in the upper part of the thorax, which is pear-shaped, spiny, and exhibits subregular, hexagonal pores, three times as broad as the bars. From each hexagon corner a small thorn arises.

_Dimensions._--Cephalis 0.04 diameter, thorax 0.25 long, 0.17 broad.

_Habitat._--Central Pacific, Station 269, depth 2900 fathoms.

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