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 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.

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.

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.

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.

3. Dictyocephalus excellens, Haeckel.

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.

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.

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, 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.

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.

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 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.

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.

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.

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.

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).

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.

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.

4. Sethocapsa nidus, Haeckel.

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.

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.

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.

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.

Section III. TRICYRTIDA, Haeckel, 1881, Prodromus, p. 426, 434.

Definition.—Cyrtoidea trithalamia, with three-jointed shell, composed of cephalis, thorax, and abdomen, with two separating transverse constrictions, an upper collar, and a lower lumbar constriction.

Synopsis of the Families and Subfamilies of Tricyrtida.

Family LXV. Podocyrtida, n. fam. (Pl. 67, 68, 71-73).

Definition.—Tricyrtida triradiata. (Cyrtoidea with a three-jointed shell, divided by two transverse constrictions into cephalis, thorax, and abdomen, and bearing three radial apophyses.)

The family Podocyrtida, composed of the Theopilida and Theoperida of my Prodromus, comprises those Cyrtoidea in which the lattice-shell is three-jointed and triradial, bearing three external apophyses. The two subfamilies differ in the shape of the basal mouth, which in the Theopilida is a simple wide opening, in the Theoperida closed by a lattice-plate. The latter are derived from the former by development of this closing plate. The phylogenetic origin of the Podocyrtida may be found in the Tripocyrtida, from which they are derived by development of an abdomen. But there are also some forms, which may be derived directly from the Plectoidea, and the origin of some other forms seems to be doubtful.

The Podocyrtida represent one of the largest groups of Cyrtoidea, very rich in numerous species, which are partly very common and widely distributed. A large number of living and fossil species has already been described and figured by Ehrenberg, (1872, 1879, loc. cit.). These mainly belong to his genera Podocyrtis, Pterocanium, Rhopalocanium, Lithornithium, &c., and many of them are very characteristic and common forms, in which the triradial structure of the three-jointed shell is visible at first view. We distinguish here twenty genera and one hundred and fifty species. The majority have a shell with a simple wide open mouth (Theopilida, fourteen genera and one hundred and eighteen species), in the minority the mouth is closed by lattice-work (Theoperida, six genera and thirty-two species).

The three joints of the shell have in the majority of Podocyrtida such a proportion that the cephalis is the smallest, the abdomen the largest, and the thorax between them intermediate in size. The cephalis bears almost constantly an apical horn; this is rarely reduced or lost; sometimes two or more horns are developed. The three radial apophyses arise originally from the base of the cephalis, and may from this point run along the shell-wall embedded in the lattice-plate of the thorax and the abdomen. They leave the latter at very different points, and form either lateral wings or terminal feet, sometimes both together. They are either solid or latticed, sometimes also branched, and of very various shape. Often only the three terminal feet surrounding the mouth have remained, whilst the ribs have disappeared.

Many species of this large family are very variable and connected with other different species by numerous transitional forms; the distinction of the genera described is also often very difficult.

Synopsis of the Genera of Podocyrtida.

Subfamily 1. Theopilida, Haeckel, Prodromus, p. 435.

Definition.—Podocyrtida with the terminal mouth of the shell open (vel Tricyrtida triradiata aperta).