Chapter XXV: Section III: TRICYRTIDA, Haeckel, 1881, Prodromus, p. 426, 434 (6)

Shell ovate, smooth. Length of the three joints = 3 : 5 : 15, breadth = 6 : 10 : 16. Cephalis hemispherical. Thorax truncate conical. Abdomen inflated, subspherical, three times as broad as the constricted mouth. Pores of nearly equal size, regular, circular in the thorax alternating, in the abdomen disposed in five to six transverse, widely distant rows.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.025 _c_ 0.075; breadth, _a_ 0.03, _b_ 0.05, _c_ 0.08.

_Habitat._--Fossil in the Tertiary rocks of Barbados.

3. _Theocampe stenostoma_, n. sp. (Pl. 66, fig. 23).

Shell about ovate, smooth. Length of the three joints = 3 : 4 : 3, breadth = 6 : 8 : 9. Cephalis hemispherical, large. Thorax and abdomen short, barrel-shaped. Both strictures deep. Abdomen three times as broad as the constricted mouth. Pores of equal size, regular, circular, disposed in oblique rows.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.04, _c_ 0.03; breadth, _a_ 0.06, _b_ 0.08, _c_ 0.09.

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

4. _Theocampe nucula_, Haeckel.

_Eucyrtidium nucula_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 29, Taf. vii. fig. 19.

Shell nearly ovate, rough. Length of the three joints = 3 : 5 : 3, breadth = 4 : 7 : 6. Cephalis hemispherical, large. Thorax and abdomen inflated. Both strictures deep. Thorax broader than the short abdomen, and twice as broad as the constricted mouth. Pores of equal size, regular, circular, regularly disposed in transverse rows: three in the cephalis, six in the thorax, and three in the abdomen.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.05, _c_ 0.03; breadth, _a_ 0.04, _b_ 0.07, _c_ 0.06.

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

5. _Theocampe cryptoprora_, Haeckel.

_Eucyrtidium cryptoprora_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 291, Taf. vii. fig. 14.

Shell ovate, thin-walled, smooth, without external strictures, but with two distinct internal annular septa. Length of the three joints = 2 : 7 : 4, breadth = 3 : 7 : 6. Cephalis, large, subspherical, {1424}hyaline; its lower half hidden in the upper part of the campanulate thorax. Mouth little constricted, nearly as broad as the truncate abdomen. All pores equal, small, regular, circular.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.07, _c_ 0.04; breadth, _a_ 0.03, _b_ 0.07, _c_ 0.06.

_Habitat._--Tropical Pacific, Stations 225 to 265, in various depths.

6. _Theocampe ovulum_, n. sp.

Shell perfectly ovate, thick-walled, smooth, without external strictures, but with two broad, internal septa. Length of the three joints = 2 : 3 : 10, breadth = 3 : 6 : 8. Cephalis and thorax together obtuse, conical, with obliquely ascending pores. Abdomen inflated, twice as broad as the constricted mouth, with ten to twelve transverse rows of pores. All pores equal, small, regular, circular.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.03, _c_ 0.1; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.08.

_Habitat._--Fossil in Tertiary rocks of Barbados and Sicily.

7. _Theocampe cassis_, Haeckel.

_Eucyrtidium cassis_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 291, Taf. vii. fig. 20.

Shell bottle-shaped, thin-walled, with slight collar, but deep lumbar stricture. Length of the three joints = 3 : 8 : 6, breadth = 2 : 7 : 7. Cephalis ovate. Thorax campanulate. Abdomen inflated, twice as broad as the constricted mouth. Pores equal, regular, circular, disposed in quincuncial rows.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.08. _c_ 0.06; breadth, _a_ 0.02, _b_ 0.07, _c_ 0.07.

_Habitat._--Tropical Pacific (Philippines), Station 206, depth 2100 fathoms.

Subgenus 2. _Theocamptra_, Haeckel.

_Definition._--Pores of the thorax and the abdomen of different sizes or dissimilar forms.

8. _Theocampe sphærothorax_, n. sp. (Pl. 66, fig. 25).

Shell almost ovate, rough. Length of the three joints = 2 : 5 : 10, breadth = 3 : 8 : 8. Cephalis hemispherical. Thorax nearly spherical, truncate. Abdomen ovate, twice as broad as the constricted mouth. Pores subregular, circular, quincuncially disposed, in the abdomen twice as broad as in the thorax, and four times as broad as in the cephalis.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.05, _c_ 0.1; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.08.

_Habitat._--Central Pacific, Stations 263 to 274, depth 2350 to 2925 fathoms.

{1425}9. _Theocampe versipellis_, Haeckel.

_Eucyrtidium versipellis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 72, Taf. xi. fig. 14.

Shell slenderly ovate, rough. Length of the three joints = 3 : 5 : 13, breadth = 4 : 8 : 9. Cephalis subspherical, without pores. Thorax hemispherical. Abdomen inflated, twice as broad as the constricted mouth. Pores subregular, circular, quincuncially disposed, in the abdomen three times as broad as in the thorax.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.05, _c_ 0.13; breadth, _a_ 0.04, _b_ 0.08, _c_ 0.09.

_Habitat._--Fossil in Barbados.

10. _Theocampe megalopora_, Haeckel.

_Eucyrtidium megaloporum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 291, Taf. vii. fig. 19.

Shell almost ovate, with two distinct strictures. Length of the three joints = 2 : 6 : 3, breadth = 3 : 6 : 4. Cephalis hemispherical. Thorax ovate, inflated. Abdomen inversely ovate, two to three times as broad as the constricted mouth. Pores subregular, circular, quincuncially disposed, twice as broad in the large thorax as in the smaller abdomen.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.03; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.04.

_Habitat._--Central Pacific, Station 267, depth 2700 fathoms.

11. _Theocampe collaris_, n. sp. (Pl. 66, fig. 18).

Shell almost ovate, with two distinct strictures. Length of the three joints = 3 : 3 : 6, breadth = 4 : 5 : 7. Cephalis obtuse conical, with five or six transverse rows of small pores. Thorax truncate conical, with longitudinal furrows, each of which contains a single pore. Abdomen inflated, with five or six distant, transverse rows of small, circular pores.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.03, _c_ 0.06; breadth, _a_ 0.04, _b_ 0.05, _c_ 0.07.

_Habitat._--South Pacific, Station 295, depth 1500 fathoms.

12. _Theocampe gemmata_, Haeckel.

_Eucyrtidium gemmatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf. x. fig. 6.

Shell slenderly ovate, smooth, with two internal annular septa. Length of the three joints = 1 : 1 : 4, breadth = 1 : 2 : 3. Cephalis campanulate, nearly as large as the truncate, conical thorax, both with small, irregular, obliquely descending pores. Abdomen broader, twice as broad as the constricted mouth, with numerous longitudinal ribs, alternating with single rows of small, circular pores. (This and the following allied species approach to _Cycladophora_, by the abdominal ribs.)

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.02, _c_ 0.07; breadth, _a_ 0.025, _b_ 0.035, _c_ 0.045.

_Habitat._--Fossil in Barbados.

{1426}13. _Theocampe costata_, n. sp. (Pl. 66, fig. 24).

Shell almost ovate, with two sharp strictures. Length of the three joints = 2 : 4 : 8, breadth = 3 : 5 : 7. Cephalis hemispherical. Thorax twice as large, also hemispherical, both with regular, circular, quincuncial pores. Abdomen broader, with numerous longitudinal ribs, alternating with longitudinal rows of larger pores. Mouth constricted, half as broad as the thorax.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.08; breadth, _a_ 0.03, _b_ 0.05, _c_ 0.07.

_Habitat._--Indian Ocean, Sunda Straits (Rabbe), surface.

14. _Theocampe cryptocephala_, Haeckel.

_Eucyrtidium cryptocephalum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 70, Taf. xi. fig. 11.

Shell ovate, rough, with two distinct strictures. Length of the three joints = 1 : 2 : 4, breadth = 1 : 4 : 5. Cephalis subspherical, its lower half hidden in the campanulate thorax. Abdomen subspherical, twice as broad as the constricted mouth. Pores subregular, circular, quincuncial, twice as broad in the abdomen as in the thorax.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.07; breadth, _a_ 0.025, _b_ 0.07, _c_ 0.09.

_Habitat._--Fossil in Barbados.

Subfamily 2. THEOCAPSIDA, Haeckel, 1881, Prodromus, p. 436.

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

Genus 623. _Theocapsa_,[240] Haeckel, 1881, Prodromus, p. 436.

_Definition._--#Theocapsida# (vel Tricyrtida eradiata clausa), with an apical horn, and a terminal lattice-plate on the mouth.

The genus _Theocapsa_, and the two following genera, represent together the small subfamily of Theocapsida, or of those Tricyrtida in which the mouth is closed by a lattice-plate, and external radial appendages are wanting. _Theocapsa_ may be derived from _Theocorys_ by fenestration of the constricted mouth.

Subgenus 1. _Theocapsetta_, Haeckel.

_Definition._--Thorax of about the same size as the abdomen, or somewhat larger; pores of both nearly equal in size and similar in form.

{1427}1. _Theocapsa aristotelis_, n. sp. (Pl. 66, fig. 6).

Shell subovate, smooth, with two distinct strictures. Length of the three joints = 2 : 6 : 7, breadth = 3 : 8 : 8. Cephalis hemispherical, with a conical, slender horn of about the same length. Thorax and abdomen nearly equal in size, thin-walled, smooth, with small, regular, circular pores of equal size. Basal pole rounded.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.07; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.08.

_Habitat._--Mediterranean (Gibraltar), Atlantic (Canary Islands), surface.

2. _Theocapsa plinii_, n. sp.

Shell subovate, smooth, with two indistinct strictures. Length of the three joints = 2 : 5 : 6, breadth = 3 : 7 : 7. Cephalis hemispherical, with a pyramidal, thick horn of about the same length. Thorax and abdomen of nearly equal size, thick-walled, rough, with large, regular, circular, double-edged pores of equal size (twice as large and half as numerous as in the similar preceding species).

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.06; breadth, _a_ 0.03, _b_ 0.07, _c_ 0.07.

_Habitat._--Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms.

3. _Theocapsa democriti_, n. sp. (Pl. 66, fig. 8).

Shell slender, ovate, spiny, with two distinct strictures. Length of the three joints = 3 : 5 : 6, breadth = 4 : 7 : 7. Cephalis ovate, with numerous slender horns of the same length. Thorax and abdomen with small, irregular, roundish pores of nearly equal size, armed with scattered slender spines, half as long as the cephalic horns. Basal pole hemispherical, rounded.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.05, _c_ 0.06; breadth, _a_ 0.04, _b_ 0.07, _c_ 0.07.

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

4. _Theocapsa galeni_, n. sp.

Shell broadly ovate, spiny, with two deep strictures. Length of the three joints = 2 : 7 : 6, breadth = 3 : 8 : 7. Cephalis hemispherical, with two conical, divergent horns of the same length. Thorax and abdomen with large, irregular, roundish pores of nearly equal size, armed with numerous short spines, not larger than the pores. Basal pole conical, pointed.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.07, _c_ 0.06; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.07.

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

Subgenus 2. _Theocapsilla_, Haeckel.

_Definition._--Thorax of about the same size as the abdomen, or somewhat larger; pores of the two different in size or form.

{1428}5. _Theocapsa wottonis_, n. sp. (Pl. 66, fig. 11).

Shell subovate, rough, with two deep strictures. Length of the three joints = 3 : 7 : 5, breadth = 3 : 9 : 8. Cephalis subspherical, with regular, circular, hexagonally-framed pores, and with a stout pyramidal horn of the same length. Thorax conical, with subregular, circular, double-edged pores. Abdomen hemispherical, smaller and thinner walled, with irregular, somewhat oblong pores. Basal pole rounded.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.07, _c_ 0.05; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.08.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

6. _Theocapsa gessneri_, n. sp.

Shell broadly ovate, with two deep strictures. Length of the three joints = 3 : 9 : 5, breadth = 4 : 10 : 4. Cephalis hemispherical, with a slender, conical horn of the same length. Thorax subspherical, with small, regular, circular pores. Abdomen inversely conical, with few large, somewhat oblong pores. Basal pole acute.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.09, _c_ 0.05; breadth, _a_ 0.04, _b_ 0.1, _c_ 0.04.

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

7. _Theocapsa aldrovandi_, n. sp.

Shell slender, inversely ovate, with two slight strictures. Length of the three joints = 3 : 8 : 14, breadth = 4 : 11 : 8. Cephalis subglobular, with a conical horn of the same length. Thorax also subglobular, papillate, with regular, circular, hexagonally-framed pores. Abdomen inversely conical, slender, with very small and numerous, subregular, circular pores. Basal pole ovate, pointed.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.08, _c_ 0.14; breadth, _a_ 0.04, _b_ 0.11, _c_ 0.08.

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

8. _Theocapsa malpighii_, n. sp. (Pl. 66, fig. 15).

Shell inversely ovate, with two distinct strictures. Length of the three joints = 3 : 8 : 11, breadth = 4 : 9 : 8. Cephalis hemispherical, with a conical horn of the some length Thorax hemispherical, thorny, with very small circular pores, surrounded by large, regular, hexagonal frames. Abdomen inversely campanulate, with larger circular pores, and longitudinal ribs. Basal pole blunt, conical.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.08, _c_ 0.11, breadth, _a_ 0.04, _b_ 0.09, _c_ 0.08.

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

Subgenus 3. _Theocapsomma_, Haeckel.

_Definition._--Thorax much smaller than the abdomen, pores of the two nearly equal in size and similar in form.

{1429}9. _Theocapsa linnæi_, n. sp. (Pl. 66, fig. 13).

Shell slender, subcylindrical, rough with two slight strictures. Length of the three joints = 1 : 3 : 6, breadth = 1 : 4 : 4. Cephalis hemispherical, with a pyramidal horn of twice the length (sometimes, as in the specimen figured, one or two small accessory horns occur at its base). Thorax hemispherical, thick-walled. Abdomen nearly cylindrical, twice as long as the thorax, thin-walled, with a hemispherical, rounded basal pole. The specimen figured is an abnormal one, with some deformities on the irregular abdomen; in numerous other specimens the abdomen is cylindrical, regular. Pores of the thorax and abdomen equal, very small and numerous, regular, circular, three to four times as broad as the bars.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05 to 0.06, _c_ 0.1 to 0.12; breadth, _a_ 0.03, b 0.06 to 0.07, _c_ 0.07 to 0.08.

_Habitat._--Cosmopolitan; Atlantic, Indian, and Pacific Oceans; many Stations at various depths.

10. _Theocapsa forskalii_, n. sp. (Pl. 66, fig. 9).

Shell slender, subcylindrical, smooth, with two slight strictures. Length of the three joints = 1 : 1 : 3, breadth = 1 : 2 : 2. Cephalis hemispherical, with a conical horn of half the length. Abdomen three times as long as the thorax, of the same breadth, with the same irregular, roundish pores, large and small intermingled. Basal pole rounded.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.03, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.06.

_Habitat._--North Atlantic, Canary Islands, Station 353, depth 2965 fathoms.

11. _Theocapsa wolffii_, n. sp. (Pl. 66, fig. 14).

Shell slender, spindle-shaped very thick-walled, rough, without external strictures, but with two broad internal girdles. Length of the three joints = 2 : 3 : 15, breadth = 4 : 5 : 7. Cephalis with a short horn of the same length, conical. Abdomen five times as long as the thorax, with the same subregular, circular pores. Basal pole inversely conical, with some larger, elongate pores.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.03, _c_ 0.15; breadth, _a_ 0.04, _b_ 0.05, _c_ 0.07.

_Habitat._--Mediterranean, Crete, depth 1620 fathoms (Spratt).

12. _Theocapsa pallasii_, n. sp.

Shell subovate, thorny, with two slight strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 2 : 3. Cephalis ovate, with a pyramidal horn of the same length. Thorax and abdomen with subregular, circular pores of medium size. Basal pole hemispherical. (Differs from _Theocapsa mülleri_, Pl. 66, fig. 7, mainly in the larger number and smaller size of the regular, quincuncial pores.)

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.06, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.09.

_Habitat._--Tropical Atlantic, Station 342, depth 1445 fathoms.

{1430}Subgenus 4. _Theocapsura_, Haeckel.

_Definition._--Thorax much smaller than the abdomen, pores of the two different in size or form.

13. _Theocapsa lamarckii_, n. sp. (Pl. 66, fig. 16).

Shell slenderly ovate, rough, with two distinct strictures. Length of the three joints = 1 : 2 : 7, breadth = 1 : 4 : 5. Cephalis subspherical, with a conical horn of twice the length. Thorax conical, with regular, circular pores. Abdomen three times longer, with subregular, hexagonal pores of twice the size. Basal pole hemispherical, with very large, irregular, roundish pores.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.14; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.1.

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

14. _Theocapsa cuvieri_, n. sp. (Pl. 66, fig. 10).

Shell slenderly spindle-shaped, thorny, with two slight strictures. Length of the three joints = 1 : 3 : 6, breadth = 1 : 3 : 3. Cephalis subspherical, with a conical horn of the same length. Thorax conical, spiny, with regular, circular, double-edged pores. Abdomen thinner-walled, inversely conical, with irregular, roundish pores. Basal pole acute, with a bunch of larger spines.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.12; breadth, _a_ 0.02, _b_ 0.05, _c_ 0.06.

_Habitat._--South Atlantic, Station 332, depth 2200 fathoms.

15. _Theocapsa baerii_, n. sp.

Shell slenderly spindle-shaped, smooth with two indistinct strictures. Length of the three joints = 1 : 2 : 8, breadth = 2 : 3 : 4. Cephalis hemispherical, with a thick conical horn of the same length. Abdomen four times as long as the thorax. Pores in the thorax small and numerous, regular, circular, in the abdomen twice as large, and irregularly roundish. Basal pole inversely conical, acute. (Differs from _Theocapsa wolffii_, Pl. 66, fig. 14, mainly in the shape of the pores.)

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.03, _c_ 0.12; breadth, _a_ 0.03, _b_ 0.04, _c_ 0.06.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

16. _Theocapsa rathkei_, n. sp.

Shell slenderly conical, with two slight strictures. Length of the three joints = 1 : 2 : 10, breadth = 2 : 4 : 15. Cephalis small, with a large, conical horn of three times the length. Thorax small, thorny, with small irregular, roundish pores. Abdomen very large, as long and as broad as the thorax, with irregular polygonal or roundish, very large pores, the margin of which is finely denticulate. Basal pole truncate, rounded.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.2; breadth, _a_ 0.04, _b_ 0.08, _c_ 0.3.

_Habitat._--Fossil in Barbados.

{1431}17. _Theocapsa schwannii_, n. sp.

Shell slenderly ovate, or pear-shaped, with two distinct strictures. Length of the three joints = 1 : 2 : 7, breadth = 2 : 4 : 7. Cephalis subspherical, small, with a stout, pyramidal horn of three times the length. Cavity of the thorax subspherical, its thick wall with small, regular, circular, hexagonally-framed pores. Abdomen very thick-walled, with crested bars, and very large, irregular, roundish pores. Basal pole rounded, truncate.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.14, breadth, _a_ 0.04, _b_ 0.08, _c_ 0.14.

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

18. _Theocapsa mülleri_, n. sp. (Pl. 66, fig. 7).

Shell slenderly ovate, or pear-shaped, spiny, with two indistinct strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 2 : 3. Cephalis ovate, with a stout, pyramidal horn of the same length, and with a variable number of smaller accessory horns. Pores irregular, roundish, three to four times as broad in the inflated abdomen as in the thorax. Basal pole hemispherical, spiny.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.05, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.07, _c_ 0.09.

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

19. _Theocapsa sarsii_, n. sp.

Shell pear-shaped, with two indistinct strictures. Length of the three joints = 1 : 1 : 3, breadth = 1 : 2 : 4. Cephalis with a thick horn of the same length, conical. Abdomen subspherical, very thick-walled, its pores regular, circular, twice as broad as the bars, and three times as broad as those of the thorax. Basal pole flat, rounded.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.05, _c_ 0.12; breadth, _a_ 0.05, _b_ 0.11, _c_ 0.15.

_Habitat._--Fossil in Barbados.

20. _Theocapsa darwinii_, n. sp. (Pl. 66, fig. 12).

Shell pear-shaped, with two distinct strictures. Length of three joints = 1 : 1 : 5, breadth = 1 : 2 : 5. Cephalis hemispherical, with a conical horn of twice the length. Thorax campanulate, with small, regular, circular pores. Abdomen broad, ovate, with larger, regular, circular, hexagonally-framed pores. Basal pole hemispherical.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.04, _c_ 0.2; breadth, _a_ 0.04, _b_ 0.08, _c_ 0.2.

_Habitat._--Central Pacific, Stations 263 to 274, depth 2350 to 2925 fathoms.

Genus 624. _Tricolocapsa_,[241] Haeckel.

_Definition._--#Theocapsida# (vel Tricyrtida eradiata clausa) without apical horn, with a terminal lattice-plate on the mouth.

{1432}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.

{1433}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 {1434}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.

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