The genus Tricolocapsa differs from the preceding Theocapsa in the loss of the apical horn, and exhibits therefore to it the same relation that Theocampe bears to Theocorys. In some species (Pl. 66, figs. 1, 3) a small tube begins to be developed on the cephalis, and these may perhaps be separated as a peculiar genus, Tricolopera.

Subgenus 1. Tricolocapsula, Haeckel.

Definition.—Thorax of about the same size as the abdomen, or larger.

1. Tricolocapsa theophrasti, n. sp. (Pl. 66, fig. 1).

Shell slenderly ovate, with two slight strictures. Length of the three joints = 2 : 8 : 5, breadth = 3 : 7 : 5. Cephalis hemispherical, with a larger, tube-like, cervical pore at the collar stricture. Thorax very thick-walled, with irregular, roundish, double edged pores, smaller than the bars between them. Abdomen smaller, inversely campanulate-conical, with very irregular pores. Basal pole acute.

Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.05; breadth, a 0.03, b 0.07, c 0.05.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Tricolocapsa dioscoridis, n. sp. (Pl. 66, fig. 3).

Shell short and broad, with two deep strictures. Length of the three joints = 3 : 5 : 4, breadth = 4 : 7 : 5. Cephalis hemispherical, with a larger, tube-like, cervical pore above the collar stricture. Thorax very broad, with irregular, large and spare, roundish pores. Abdomen much smaller, inversely conical, with smaller pores. Basal pole obtuse.

Dimensions.—Length of the three joints, a 0.03, b 0.05, c 0.04; breadth, a 0.04, b 0.07, c 0.05.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

3. Tricolocapsa linnæi, n. sp. (Pl. 66, fig. 5).

Shell short and broad, with two deep strictures. Length of the three joints = 1 : 4 : 2, breadth = 1 : 4 : 2. Cephalis hemispherical. Thorax thick-walled, inflated, with subregular, circular, double-edged pores. Abdomen much smaller, thin-walled, with irregular, polygonal pores. Basal pole hemispherical, rounded.

Dimensions.—Length of the three joints, a 0.02, b 0.08, c 0.05; breadth, a 0.03, b 0.08, c 0.05.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

4. Tricolocapsa decandollei, n. sp. (Pl. 66, fig. 4).

Shell subovate, with two sharp strictures. Length of the three joints = 2 : 2 : 2, breadth = 3 : 4 : 3.5. Cephalis campanulate. Thorax broader, ring-shaped. Abdomen inversely hemispherical. All three joints of the same length, thick-walled, with the same regular and peculiar reticulation, the small circular pores being surrounded by square, elevated frames.

Dimensions.—Length of the three joints, a 0.07, b 0.07, c 0.07; breadth, a 0.10, b 0.14, c 0.12.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. Tricolocapsium, Haeckel.

Definition.—Thorax much smaller than the abdomen.

5. Tricolocapsa brownii, n. sp.

Shell ovate, very thick-walled, with two indistinct strictures. Length of the three joints = 2 : 4 : 7, breadth = 3 : 7 : 10. Cephalis flat, hemispherical. Thorax truncate, conical. Abdomen inflated, inversely hemispherical. Pores regular, circular, of the same breadth as the bars, hexagonally-framed, twice as large in the abdomen as in the thorax. Basal pole rounded.

Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.07; breadth, a 0.03, b 0.07, c 0.1.

Habitat.—Fossil in Barbados.

6. Tricolocapsa schleidenii, n. sp. (Pl. 66, fig. 2).

Shell subconical, with two deep strictures. Length of the three joints = 2 : 3 : 6, breadth = 3 : 5 : 6. Cephalis subspherical. Pores subregular, circular, arranged in transverse girdles, three in the broad thorax, six in the subglobular abdomen. Basal pole rounded.

Dimensions.—Length of the three joints, a 0.02, b 0.03, c 0.06; breadth, a 0.03, b 0.05, c 0.06.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

Genus 625. Phrenocodon,^[242] n. gen.

Definition.—Theocapsida (vel Tricyrtida eradiata clausa) with an apical horn, and a lattice-plate between thorax and abdomen.

The genus Phrenocodon differs from the two preceding genera in the remarkable circumstance, that the basal lattice-plate closes not the terminal mouth itself, but the constricted opening between thorax and abdomen. It may therefore be regarded as a Sethocapsa, which has developed a third, open, abdominal joint. The cephalis bears an apical horn.

1. Phrenocodon clathrostomium, n. sp. (Pl. 70, figs. 7, 8).

Shell campanulate-conical, with two deep strictures. Length of the three joints = 2 : 6 : 3, breadth = 3 : 10 : 14. Cephalis hemispherical, with an oblique curved horn of the same length. Thorax subconical, with polygonal, roundish pores, increasing in size towards the girdle. A perfect fenestrated diaphragm, with irregular, roundish pores of very different sizes, separates the thorax from the abdomen. The latter is composed of three parallel, circular rings, which are connected by fifteen to twenty radial beams. As the middle ring is larger than the two others, the beams between the large quadrangular pores are divergent in the upper, convergent in the lower girdle. Short prolongations of the divergent beams form a coronal around the middle ring (compare fig. 7 profile, fig. 8 from below).

Dimensions.—Length of the three joints, a 0.02, b 0.06, c 0.03; breadth, a 0.03, b 0.1, c 0.14.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Phrenocodon diaphragma, n. sp.

Shell campanulate-conical, very similar to that of the preceding species, but with abdomen and proportions different. Length of the three joints = 1 : 3 : 2, breadth = 1 : 4 : 4. Abdomen cylindrical, with two or three transverse rows of large quadrangular meshes (fifteen to twenty in each row), without the characteristic inflexion of the preceding species, and without the coronal.

Dimensions.—Length of the three joints, a 0.02, b 0.06, c 0.034; breadth, a 0.02, b 0.08, c 0.08.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Section IV. STICHOCYRTIDA, Haeckel, 1862, Monogr. d. Radiol., p. 280, 312 (Pls. 75-80).

Definition.—Cyrtoidea polythalamia, with annulated shell, divided by three to six or more transverse, horizontal constrictions, into four to seven or more annular joints. (The first joint represents the cephalis, the second the thorax, the third the abdomen, all the following joints together a post-abdomen.)

Synopsis of the three Families and six Subfamilies of Stichocyrtida.

Family LXVIII. Podocampida, n. fam.

Definition.—Stichocyrtida triradiata. (Cyrtoidea with an annulated shell, divided by three or more transverse constrictions into four or more annular joints, and bearing three radial apophyses).

The family Podocampida comprises those Cyrtoidea in which the lattice-shell is composed of numerous (four to eight or more) annular joints, and bears three external radial apophyses. It may be divided into two subfamilies, differing in the shape of the terminal mouth. This is a simple wide opening in the Stichopilida (and the united Artopilida), closed by a lattice-plate in the Stichoperida (and the united Artoperida). The phylogenetic origin of the Podocampida may be found in the Podocyrtida (p. 1314).

Very few forms only of the Podocampida were hitherto known, viz., Stichopilium (Pterocodon) davisianum, and three fossil species from Barbados, figured by Ehrenberg; Artopera loxia (united by him with Lithornithium), and two species of Pteropilium (sphinx and bombus, both united by him with the three-jointed Pterocanium). In general, the triradiate Stichocyrtida are much rarer and much poorer in specific forms than the triradiate Tricyrtida, their ancestors. We have observed altogether only forty-four species, thirty Stichopilida, and fourteen Stichoperida; the former are disposed among seven, the latter among three genera.

The three radial apophyses appear either as lateral ribs or prominent wings in the thorax (Pl. 77, fig. 8-12), or as three terminal feet around the mouth (Pl. 97, fig. 15). Sometimes the ribs are replaced by three radial combs, or rows of spines, and these may be united by three divergent beams, forming three vaulted bridges with numerous bows (Pl. 75, figs. 10, 11). The lateral wings or ribs, as well as the terminal feet, are either solid or fenestrated.

Synopsis of the Genera of Podocampida.

Subfamily 1. Stichopilida, Haeckel, 1881, Prodromus, p. 439.

Definition.—Podocampida with the terminal mouth of the shell open (vel Stichocyrtida triradiata aperta).

Genus 626. Stichopilium,^[243] Haeckel, 1881, Prodromus, p. 439.

Definition.—Stichopilida (vel Stichocyrtida triradiata aperta) with three solid lateral ribs or wings, without terminal feet. Cephalis with a horn.

The genus Stichopilium is the most primitive among all Stichocyrtida, and represents perhaps the common ancestral form of this family. The shell is composed of four or more joints (sometimes ten to twelve), has a wide open terminal mouth, and three lateral solid wings or ribs (sometimes a little latticed on the base). Stichopilium may be derived from Theopilium or Pterocorys by addition of new terminal joints.

Subgenus 1. Triacartus, Haeckel, 1881, Prodromus, p. 437.

Definition.—Shell with three annular strictures, and four distinct joints.

1. Stichopilium cortina, n. sp.

Shell ovate, with three sharp strictures. Length of the four joints = 2 : 6 : 3 : 4. Cephalis subspherical, with a slender pyramidal horn of twice the length. The three edges of the horn are prolonged into three strong divergent ribs, along the three first joints, and into three free conical lateral spines, directed downwards, on the end of the third joint. The fourth joint is subcylindrical; its circular, terminal mouth half as broad as the third joint, which is the broadest. Pores small, regular, hexagonal, with thin bars.

Dimensions.—Length of the shell (with four joints) 0.15, breadth 0.08. Length of the single joints, a 0.02, b 0.06, c 0.03, d 0.04.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Stichopilium costatum, n. sp.

Shell conical, or nearly pyramidal, with three distinct strictures. Length of the four joints = 3 : 5 : 8 : 4. Cephalis subconical, with a stout pyramidal horn of the same length. Thorax campanulate, with six longitudinal ribs, from three of which in the middle arise three horizontal, conical, free spines or wings, about as long as the cephalis. The third large prismatic joint bears twelve parallel ribs, six new ribs being intercalated between the six former. Fourth joint short, cylindrical, without ribs, the wide open mouth not constricted, nearly as broad as the third joint, which is the broadest. Pores small, irregular, polygonal, or roundish.

Dimensions.—Length of the shell (with four joints) 0.2, breadth 0.12. Length of the single joints, a 0.03, b 0.05, c 0.08, d 0.04.

Habitat.—North Pacific, Station 244 (off Japan), depth 2900 fathoms.

3. Stichopilium bicorne, n. sp. (Pl. 77, fig. 9).

Shell conical, with three slight strictures. Length of the four joints = 4 : 14 : 5 : 3. Cephalis large, conical, with two stout pyramidal, divergent horns of twice the length. From its base (in the middle of the collar stricture) arise three internal, downwardly divergent ribs, which are prolonged on the outside of the upper half of the thorax into three stout, pyramidal, lateral spines (similar to the horns). The fourth joint, with wide open mouth, was the broadest, but not fully developed in the single specimen observed. Pores subregular, hexagonal, with thin bars.

Dimensions.—Length of the shell (with four joints) 0.02, breadth 0.09. Length of the single joints, a 0.02, b 0.07, c 0.025, d 0.015.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

4. Stichopilium davisianum, Haeckel.

Shell campanulate, conical, with three slight strictures. Length of the four joints = 2 : 3 : 4 : 3. Cephalis hemispherical, with few small pores and a short conical horn. Thorax campanulate, with larger circular pores, and three recurved, divergent, lateral wings of the same length. Third and fourth joints each with three transverse rows of very large hexagonal pores. The similar form described by Ehrenberg as Cycladophora davisiana, is either a mutilated specimen, or belongs to Lithostrobus.

Dimensions.—Length of the shell (with four joints) 0.12, breadth 0.08. Length of the single joints, a 0.02, b 0.03, c 0.04, d 0.03.

Habitat.—North Atlantic, Greenland, depth 1000 to 1500 fathoms.

5. Stichopilium campanulatum, n. sp. (Pl. 77, fig. 11).

Shell campanulate, with three slight strictures. Length of the four joints = 3 : 5 : 5 : 4. Cephalis subovate, with an internal rod-cross, and a stout pyramidal horn of the same length. From the middle of the collar stricture arise three divergent collar beams, which descend in the upper half of the campanulate thorax as three divergent ribs, and are prolonged into three free horizontal spines. (In the specimen figured these three wings are very short; in another specimen, found afterwards, there were three solid, pyramidal, horizontal spines, as long as the cephalic horn.) The third joint is the broadest, of about the same length as the fourth. (The annular septum between the two latter is by a mistake not figured). Pores subregular, circular, hexagonally framed.

Dimensions.—Length of the shell (with four joints) 0.17, breadth 0.12. Length of the single joints, a 0.03, b 0.05, c 0.05, d 0.04.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

6. Stichopilium triserratum, n. sp.

Shell slenderly campanulate, with three deep strictures. Length of the four joints = 2 : 4 : 6 : 3. Cephalis hemispherical, with a stout pyramidal horn three times the length. The three edges of the horn are prolonged into three strong prominent ribs along the three first joints; each rib bears a series of stout, irregular, triangular teeth. The fourth joint is without ribs; its constricted mouth is half as broad as the third (broadest) joint. Pores subregular, circular.

Dimensions.—Length of the shell (with four joints) 0.15, breadth 0.08. Length of the single joints, a 0.02, b 0.04, c 0.06, d 0.03.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Subgenus 2. Stichopilidium, Haeckel.

Definition.—Shell with four or more annular strictures and five or more joints.

7. Stichopilium macropterum, Haeckel.

Shell slenderly conical, with five deep strictures. Length of the six joints = 2 : 5 : 4 : 3 : 3 : 6. Cephalis hemispherical, with a stout conical horn of twice the length. Thorax campanulate, with three large, triangular, widely divergent wings or ribbed solid spines, nearly as long as the shell. The breadth of the joints increases gradually; the last joint is the broadest, with wide open mouth. Pores subregular, circular.

Dimensions.—Length of the shell (with six joints) 0.23, breadth 0.1. Length of the single joints, a 0.02, b 0.05, c 0.04, d 0.03, e 0.03, f 0.06.

Habitat.—Fossil in Barbados.

8. Stichopilium pectinatum, n. sp.

Shell slenderly conical, with nine sharp strictures. All ten joints have nearly equal length, and increase gradually in breadth; the last joint is the broadest, and twice as long as each of the others, with wide open mouth. Cephalis subspherical, with a conical horn of the same length. Each joint (excepting the first and the last) bears three lateral, nearly horizontal spines, and the bases of all the spines are connected by three longitudinal, divergent ribs. Pores subregular, hexagonal. (Similar to Stichopera pectinata, Pl. 75, fig. 11.)

Dimensions.—Length of the shell (with ten joints) 0.32, breadth 0.1.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

9. Stichopilium thoracopterum, n. sp.

Shell slenderly ovate, twice as long as broad, with eleven slight annular strictures. The twelve joints (excepting the second) are of nearly equal length, or alternately longer and shorter. The eighth joint is the broadest, one and a half times as broad as the slightly constricted mouth. Cephalis small, hemispherical, with a pyramidal horn of twice the length. Thorax (or second joint) campanulate, twice to three times as long as each of the eleven other joints, with three longitudinal ribs, prolonged into three divergent, slender, free spines. Pores small, regular, hexagonal.

Dimensions.—Length of the shell (with twelve joints) 0.22, breadth 0.11. Length of each joint (on an average) 0.015 to 0.017, thorax 0.035.

Habitat.—South Pacific, Station 296, depth 1825 fathoms.

Genus 627. Artopilium,^[244] Haeckel, 1881, Prodromus, p. 437.

Definition.—Stichopilida (vel Stichocyrtida triradiata aperta) with three latticed lateral ribs or wings, without terminal feet. Cephalis with a horn.

The genus Artopilium (including also the genera Trictenartus, Pterocorythium, Stichopterygium, and Clathropyrgus of my Prodromus) has a shell of the same form as the preceding Stichopilium, but it differs in the fenestration of the three lateral ribs or wings, which in the latter are solid. The limit between the two genera is often not sharp. Artopilium may be also derived from the three-jointed Dictyoceras by addition of new terminal joints.

Subgenus 1. Trictenartus, Haeckel, 1881, Prodromus, p. 437.

Definition.—Shell with three annular strictures and four joints.

1. Artopilium elegans, n. sp. (Pl. 75, fig. 1).

Shell three-sided pyramidal, with three annular strictures. Length of the four joints = 1 : 2 : 9 : 3. Cephalis small, hemispherical, with two large, prismatic, divergent horns of three times the length. The three prominent edges of the second and third joints are finely latticed and dentated, and at the basal end of the third joint are prolonged into three stout, free, pointed, pyramidal, divergent wings, about as long as the horns. The fourth joint is only as long as the second, three-sided prismatic, its wide triangular mouth is armed with six parallel, vertical, slender teeth (two between every three wings). Network very delicate and regular, in the first and second joints with circular, in the third and fourth joints with small hexagonal meshes.

Dimensions.—Length of the shell (with four joints) 0.3, breadth of the third joint 0.3, of the fourth 0.2. Length of the single joints, a 0.02, b 0.04, c 0.18, d 0.06.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

2. Artopilium longicorne, n. sp. (Pl. 77, fig. 10).

Shell subovate, with three internal annular septa. Length of the four joints = 2 : 3 : 2 : 6. Cephalis hemispherical, with a very large three-sided prismatic horn, nearly as long as the shell. Along the three following joints arise three broad, triangular, latticed wings, about as long as the shell. The fourth joint is the broadest, and twice as broad as the constricted mouth. Pores in the two upper joints regular, circular, in the two lower and the three wings hexagonal.

Dimensions.—Length of the shell (with four joints) 0.13, breadth 0.09. Length of the single joints, a 0.02, b 0.03, c 0.02, d 0.06.

Habitat.—Central Pacific, Station 263, depth 2650 fathoms.

3. Artopilium cyrtopterum, n. sp. (Pl. 77, fig. 12).

Shell subovate, with three sharp strictures. Length of the four joints = 1 : 2 : 3 : 3. Cephalis subspherical, with a stout, pyramidal horn of twice the length. Along the second and third joints arise three broad, triangular, latticed wings, about half as long as the shell. The third joint is the broadest, and twice as broad as the constricted mouth. Pores subregular, circular.

Dimensions.—Length of the shell (with four joints) 0.18, breadth 0.1. Length of the single joints, a 0.02, b 0.04, c 0.06, d 0.06.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

Subgenus 2. Clathropyrgus, Haeckel, 1881, Prodromus, p. 439.

Definition.—Shell with four or more annular strictures, and five or more joints.

4. Artopilium trifenestra, n. sp. (Pl. 75, fig. 7).

Shell tower-shaped, nearly cylindrical, with nine deep strictures. The ten joints are of different lengths and breadths. The third and fourth joints are the longest, twice as long as the first, fifth, sixth, eighth, and ninth joints. The third, seventh, and tenth joints are the broadest, and nearly twice as broad as the second and ninth joints. The mouth of the last joint is dilated. The second joint bears three divergent ribs, and the third joint (as prolongations of these) three broad, triangular, lattice-wings, and between the latter three large, ovate openings or windows, recalling those in Clathrocanium (Pl. 64). Cephalis subspherical, with a pyramidal horn of twice the length. Pores subregular, circular, hexagonally framed.

Dimensions.—Length of the shell (with ten joints) 0.28, of the first and ninth joints 0.02, of the third and fourth joints 0.04; breadth of the third and seventh joints 0.08, of the second and ninth joints 0.04.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

5. Artopilium trigonopterum, n. sp.

Shell in the upper half campanulate-conical, in the lower half cylindrical, with seven internal septa. The four middle joints are equal in length, each about twice as long as each of the two first and of the two last joints. Cephalis hemispherical, with a conical horn of the same length. Along the first three joints arise three broad, triangular, lattice-wings. Pores small, regular, hexagonal, in the wings and the two first joints circular. The five lower joints are of equal breadth.

Dimensions.—Length of the shell (with eight joints) 0.2, breadth 0.1. Length of the four middle joints, each about 0.034, of the two first and the two last, each 0.017.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

6. Artopilium cornutella, n. sp.

Shell slenderly conical, without external strictures, but with twelve to fifteen internal annular septa. All thirteen to sixteen joints are nearly equal or slightly different in length, but increase gradually in breadth. Along the whole shell arise three narrow, divergent lattice-wings, increasing in height towards the wide open mouth. Pores subregular, square, in three to four transverse rows on each joint, half as large in the three wings as in the joints. Cephalis small, subspherical, with a conical horn of twice the length. (In the specimen described the axis of the slender cone was straight, in another incomplete specimen curved; this may perhaps be a separate species, Artopilium curvatum.)