Chapter XXII: Section III: TRICYRTIDA, Haeckel, 1881, Prodromus, p. 426, 434 (3)

Shell three-sided prismatic, with three broad and long hyaline wings, which are prolonged from the collar stricture almost to the basal end, with three parallel edges. Length of the three joints = 2 : 8 : 10, breadth = 3 : 9 : 8. Cephalis hemispherical, with a conical horn of the same length. Thorax subspherical; abdomen inversely ovate; pores of both small, regular, circular, of equal size.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.1; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.08.

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

2. _Theopera pyramis_, Haeckel.

_Rhopalocanium_ sp., Bury, 1862, Polycystins of Barbados, pl. xvii. fig.
8.

Shell three-sided pyramidal, with three broad and long hyaline wings, which are prolonged from the collar stricture almost to the basal end, with three diverging edges. Length of the three joints = 3 : 8 : 11, breadth = 4 : 8 : 9. Cephalis subspherical, with a conical horn of the same length. Thorax hemispherical; abdomen inversely campanulate. Pores in the abdomen twice to three times as broad as in the thorax, subregular, circular. Differs from the preceding species mainly in the broader pyramidal form and the divergence of the wings.

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

_Habitat._--Fossil in Barbados.

3. _Theopera fusiformis_ (Pl. 67, fig. 5).

Shell nearly spindle-shaped, rough, with two slight strictures. Length of the three joints = 2 : 3 : 6, breadth = 2 : 5 : 4. Cephalis hemispherical, large, with an oblique conical horn of the same length. Thorax hemispherical; abdomen inversely conical. Pores irregular, roundish, of very {1358}different sizes. Three wings short, broad, diverging, triangular, and striated, embracing at the base the lumbar stricture, the lower third of the thorax and the upper third of the abdomen.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.06, _c_ 0.12; breadth, _a_ 0.045, _b_ 0.1, _c_ 0.08.

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

4. _Theopera luscinia_, Haeckel.

_Lithornithium luscinia_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. iv. fig. 9.

Shell slenderly ovate, with distinct collar, but indistinct lumbar strictures. Length of the three joints = 1 : 3 : 6, breadth = 1 : 5 : 5. Cephalis hemispherical, with a slender cylindrical horn of three times the length, bearing a spindle-shaped spinulate top (like a fir-cone). Pores subregular, circular, twice as broad in the abdomen as in the thorax. Three wings arising with broad triangular base, embracing the lower third of the thorax and the upper third of the abdomen, prolonged into three slender diverging spines, as long as the shell.

_Dimensions._--Length of the three joints _a_ 0.015, _b_ 0.05, _c_ 0.1; breadth, _a_ 0.02, _b_ 0.07, _c_ 0.07.

_Habitat._--Fossil in Barbados.

5. _Theopera chytropus_, n. sp. (Pl. 67, fig. 6).

Shell slender, ovate, with distinct collar, but indistinct lumbar stricture. Length of the three joints = 1 : 2 : 5, breadth = 1 : 3 : 3. Cephalis hemispherical, with a conical horn of the same length. Pores in the thorax and abdomen of similar shape, irregular, roundish. Three wings with broad triangular base attached at the upper half of the shell, in the lower half free, diverging, with a spinulate knob at the distal end.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.06, _c_ 0.15; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.09.

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

6. _Theopera cortina_, n. sp. (Pl. 67, fig. 8).

Shell slender, ovate, with distinct collar, but indistinct lumbar stricture. Length of the three joints = 1 : 2 : 6, breadth 1 : 4 : 4. Cephalis subspherical, with an elegant pyramidal horn of three times the length, bearing an ovate, spinulate knob. Pores subregular, circular, two or three times as large in the abdomen as in the thorax. The three wings are slightly elevated small ribs on the thorax, arise with broad, triangular, striated bases in the upper half of the abdomen, and are prolonged into three slender diverging feet, which are as long as the shell, and bear a spinulate, ovate knob at the distal end.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.13; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.08.

_Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms.

{1359}Genus 598. _Rhopalocanium_,[215] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Theoperida# (vel Tricyrtida triradiata clausa) with three lateral wings on the sides of the inversely conical abdomen, which bears no vertical terminal horn on the basal apex.

The genus _Rhopalocanium_, and the closely allied _Rhopalatractus_ which follows, differ from the preceding _Theopera_, their probable ancestral form, in the origin of the three lateral wings from the inversely conical abdomen, the thorax bearing no wings. The upper part of the wing bases, which arose formerly from the thorax, is here reduced and lost.

1. _Rhopalocanium lasanum_, n. sp. (Pl. 67, fig. 10).

Shell subovate, with two distinct strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 3 : 4. Cephalis hemispherical, with a conical, dimpled horn of twice the length. Thorax subconical, abdomen campanulate, both with irregular, circular pores. Three wings cylindrical, divergent, about as long as the shell, striated, with an ovate, dimpled knob at the distal end, their broad triangular base being attached to the upper half of the abdomen. (Form rather variable.)

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.07, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.12.

_Habitat._--Central Pacific, Stations 263 to 268, depth 2650 to 3000 fathoms.

2. _Rhopalocanium ornatum_, Ehrenberg.

_Rhopalocanium ornatum_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 9;
Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 82, Taf. xvii. fig. 8.

Shell nearly spindle-shaped, with two distinct strictures. Length of the three joints = 1 : 3 : 6, breadth = 1 : 4 : 3. Cephalis hemispherical, with a stout, cylindrical horn of twice the length, bearing a dimpled cone. Thorax ovate, campanulate. Abdomen inversely conical. Pores subregular, circular, twice as large in the thorax as in the abdomen. Three wings compressed, slender, divergent, slightly longer than the abdomen, bearing an ovate, dimpled cone at their distal end, with the broad, triangular, striated base attached to the upper third of the abdomen.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.12; breadth, _a_ 0.025, _b_ 0.08, _c_ 0.07.

_Habitat._--Fossil in Barbados.

3. _Rhopalocanium cortinium_, n. sp.

Shell slender, ovate, nearly of the same form as, and with similar fenestration to that of _Theopera cortina_, (Pl. 67, fig. 8). It differs from the latter mainly by the absence of the three thoracic ribs, characteristic of _Theopera_. Length of the three joints = 1 : 2 : 6, breadth = 1 : 4 : 4. The {1360}three wings arise by a broad, triangular, striated base from the upper half of the abdomen, below the lumbar stricture. The cephalic horn and the three divergent wings are shorter, and at the distal end not so much thickened as in _Theopera cortina_.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.045, _c_ 0.12; breadth, _a_ 0.03, _b_ 0.07, _c_ 0.08.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

4. _Rhopalocanium pythia_, n. sp.

_Rhopalocanium ornatum_, Bury, 1862, Polycystins of Barbados, pl. vi.
fig. 1.

Shell nearly ovate, with two deep strictures. Length of the three joints = 1 : 4 : 8, breadth = 1 : 4 : 4. Cephalis subspherical, with a conical horn of three times the length. Thorax inflated, abdomen inversely campanulate and prolonged into a short, conical, latticed tube. Pores subregular, circular. Three wings slender, as long as the abdomen, arising by a broader base from the uppermost part of the abdomen, their thickened end being curved inwards.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.07, _c_ 0.15; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.07.

_Habitat._--Fossil in Barbados.

5. _Rhopalocanium delphicum_, n. sp. (Pl. 67, fig. 9).

Shell nearly spindle-shaped, with two deep strictures. Length of the three joints = 1 : 2 : 4, breadth = 1 : 3 : 3. Cephalis hemispherical, with a slender, conical, curved horn, as long as the hemispherical thorax. Abdomen inversely campanulate, prolonged into a short, conical, latticed tube. Pores subregular, circular. Three wings arising by a narrow base from the uppermost part of the abdomen, slender, cylindrical, S-shaped, curved, divergent, with a thick scaly appendix like a fir-cone at the distal end.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.07, _c_ 0.14; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.08.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

Genus 599. _Rhopalatractus_,[216] Haeckel, 1881, Prodromus, p. 437.

_Definition._--#Theoperida# (vel Tricyrtida triradiata clausa) with three lateral wings on the sides of the inversely conical abdomen, which bears a vertical terminal horn on the basal apex.

The genus _Rhopalatractus_, one of the most remarkable forms of Tricyrtida, differs from the preceding _Rhopalocanium_, its ancestral form, in the production of a vertical, basal horn, which descends from the basal apex of the inversely conical abdomen, and is opposed to the upper apical horn of the cephalis. The shell becomes here, therefore, exquisitely spindle-shaped.

{1361}1. _Rhopalatractus pentacanthus_, n. sp. (Pl. 68, fig. 11).

Shell very thick-walled, with two sharp strictures. Length of the three joints = 1 : 6 : 8, breadth = 1 : 6 : 7. Cephalis hemispherical, with conical cavity, and a conical horn of twice the length. Thorax subspherical, separated from the abdomen by a deep lumbar stricture, with small, regular, circular, hexagonally-framed pores. Abdomen three-sided prismatic, with three strong, prominent, wing-shaped edges, which are slightly divergent towards the base, and prolonged into three pyramidal feet about as long as the thorax. Pores of the abdomen disposed in longitudinal rows, which are separated by denticulate crests. Abdominal base inversely pyramidal, and prolonged into a very large, cylindrical, basal, axial spine, nearly as long as the whole shell.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.12, _c_ 0.15; breadth, _a_ 0.03, _b_ 0.11, _c_ 0.14.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

2. _Rhopalatractus foveolatus_, n. sp. (Pl. 68, fig. 10).

Shell slenderly ovate, thick-walled, with rough, dimpled surface. Length of the three joints = 1 : 3 : 5, breadth = 2 : 4 : 4. Cephalis hemispherical, with spherical cavity, and a thick, conical spine of the same length. Thorax subspherical, with subregular, circular pores. Abdomen inversely conical, with larger, irregular, roundish pores, prolonged at the distal end into a cylindrical, axial, basal spine of about half its length. From the middle part of the abdomen arise three lateral, conical feet, which are slightly curved and divergent downwardly, scarcely as long as the basal spine. All five spines are dimpled.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.1; breadth _a_ 0.04, _b_ 0.08, _c_ 0.08.

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

3. _Rhopalatractus fusiformis_, n. sp.

Shell slender, spindle-shaped, nearly of the same form as in the preceding species. Length of the three joints = 1 : 2 : 6, breadth = 1 : 2 : 2. Cephalis subspherical, with a cylindrical horn three times the length. Pores subregular, circular, of equal breadth in the thorax and in the abdomen, which is prolonged into a cylindrical, axial, basal spine of the same length. From the upper third of the abdomen arise, from a broad triangular base, three conical wings of half the length, divergent and slightly curved inwards.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.05, _c_ 0.15; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.06.

_Habitat._--Central Pacific, Station 263, depth 2650 fathoms.

4. _Rhopalatractus fenestratus_, n. sp. (Pl. 68, fig. 12).

_Dictyatractus fenestratus_, Haeckel, 1881, Prodromus et Atlas.

Shell nearly spindle-shaped, with two distinct strictures. Length of the three joints = 1 : 3 : 6, breadth = 1 : 4 : 4. Cephalis hemispherical, with a large, club-shaped horn, nearly as long as the abdomen, sulcated by longitudinal ribs, which are elegantly denticulate in the distal half. Thorax {1362}subspherical. Abdomen subovate, prolonged into a pyramidal, axial, basal spine, half as long as the thorax. Pores subregular, circular. From the upper half of the abdomen arise three stout, lateral, diverged wings of about the same length, which are curved inwards and fenestrated both at the broad triangular base and at the thickened, three-edged distal end.

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

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

Genus 600. _Lithochytris_,[217] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Theoperida# (vel Tricyrtida triradiata clausa) with a three-sided pyramidal abdomen, the triangular base of which is prolonged at the three corners into three terminal feet.

The genus _Lithochytris_ differs from all the other Theoperida in the absence of lateral wings and the possession of three divergent, terminal feet, which arise from the three corners of the three-sided pyramidal abdomen. It repeats, therefore, among the Tricyrtida, that characteristic formation which _Sethochytris_ and _Tetrahedrina_ represent among the Dicyrtida. Some species may be derived from _Pterocanium_, other species from _Podocyrtis_, by the development of a lattice-plate closing the terminal mouth.

Subgenus 1. _Lithochytrodes_, Haeckel.

Three feet of the abdomen solid, not fenestrated, representing external apophyses of the triangular shell-base.

1. _Lithochytris cortina_, n. sp. (Pl. 67, fig. 12).

Shell three-sided pyramidal, without external strictures, but with two internal girdles. Length of the three joints = 2 : 2 : 5, breadth = 3 : 4 : 6. Cephalis large, truncate-pyramidal, with nine deep divergent ribs (and nine longitudinal rows of pores between them), and with a stout pyramidal horn of half the length. The three prominent edges of the thorax and abdomen are prolonged over the base of the pyramid into three very stout, solid, subovate feet, about as long as the thorax.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.04, _c_ 0.1; breadth, _a_ 0.06, _b_ 0.08, a 0.12.

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

2. _Lithochytris pyriformis_, n. sp. (Pl. 67, fig. 13).

Shell pyramidal, nearly pear-shaped, with two distinct strictures. Length of the three joints = 1 : 1 : 3, breadth = 1 : 2 : 3. Cephalis large, pear-shaped, with a short pyramidal horn of half the {1363}length. Thorax and abdomen rounded, without prominent edges. Three basal feet pyramidal, solid, nearly vertical, as long as the thorax. Pores irregular, roundish, in the abdomen large, twice to three times as broad as in the thorax.

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

_Habitat._--Tropical Atlantic, Station 348, depth 2450 fathoms.

3. _Lithochytris tripodium_, Ehrenberg.

_Lithochytris tripodium_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 76, Taf. iv. fig. 11.

Shell pyramidal, nearly pear-shaped, with two distinct strictures. Length of the three joints = 1 : 2 : 4, breadth = 1 : 2 : 5. Cephalis with a horn of the same length, conical. Thorax and abdomen rounded, without prominent edges. Three basal feet conical, solid, strongly divergent, shorter than the thorax. Pores subregular, circular, twice as broad in the abdomen as in 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_ 0.1.

_Habitat._--Fossil in Barbados.

Subgenus 2. _Lithochytridium_, Haeckel.

_Definition._--Three feet of the abdomen hollow and fenestrated, representing direct protuberances or corner prolongations of the triangular shell-base.

4. _Lithochytris galeata_, n. sp. (Pl. 67, fig. 16).

Shell pyramidal, with two sharp strictures. Length of the three joints = 1 : 1 : 4, breadth = 1 : 2 : 4. Cephalis subspherical, with an oblique pyramidal horn of the same length. Thorax somewhat larger. Abdomen inflated, with three sharp, prominent edges, which are prolonged over the shell-base into three pyramidal, hollow, and fenestrated feet, longer than the thorax. Pores subregular, circular, twice as broad in the abdomen as in the thorax.

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

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

5. _Lithochytris pileata_, Ehrenberg.

_Lithochytris pileata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 76, Taf. v. fig. 3.

Shell three-sided pyramidal, with deep collar, but indistinct lumbar stricture. Length of the three joints = 2 : 2 : 9, breadth = 3 : 5 : 10. Cephalis with a conical horn of the same length, pear-shaped. Thorax very short and broad. Abdomen inflated, with three sharp, prominent edges, which {1364}are prolonged over the shell-base into three pyramidal, hollow and fenestrated feet, the lower edge of which is horizontal. Pores regular, circular, of equal size in the thorax and abdomen.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.02, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.05, _c_ 0.1.

_Habitat._--Fossil in Barbados.

6. _Lithochytris lucerna_, n. sp. (Pl. 67, fig. 14).

Shell three-sided pyramidal, with two indistinct strictures. Length of the three joints = 1 : 2 : 5, breadth = 2 : 3 : 8. Cephalis small, with a horn of the same length, conical. Thorax with subspherical cavity. Abdomen with three rounded, prominent edges, which are prolonged over the shell-base into three conical, hollow, and fenestrated feet, twice as long as the thorax, with a thick, pyramidal, terminal spine. Pores subregular, circular, of equal size in the thorax and abdomen.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.1; breadth, _a_ 0.04, _b_ 0.06, _c_ 0.16.

_Habitat._--South Pacific, Station 297, depth 1775 fathoms.

7. _Lithochytris lanterna_, n. sp. (Pl. 67, fig. 11).

Shell three-sided pyramidal, with two distinct strictures. Length of the three joints = 1 : 2 : 4, breadth = 1 : 3 : 6. Cephalis small, with a pyramidal slender horn of twice the length. Thorax with subspherical cavity. Abdomen with three sharp prominent edges, which are prolonged over the convex shell-base into three slender, prismatic, hollow, fenestrated feet, strongly divergent, twice as long as the thorax (seen in fig. 11 from the vaulted base). Pores circular, twice as broad in the abdomen as in the thorax.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.08; breadth, _a_ 0.02, _b_ 0.06, _c_ 0.12.

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

8. _Lithochytris pyramidalis_, Ehrenberg.

_Lithochytris pyramidalis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 76, Taf. v. fig. 1.

Shell three-sided pyramidal, without external strictures, but with two internal transverse girdles. Length of the three joints = 1 : 2 : 6, breadth = 2 : 4 : 8. Cephalis with a short horn of half the length, conical. Cavity of the thorax subspherical. Abdomen with three rounded edges, prolonged over the concave base into three pyramidal, hollow, and fenestrated feet, twice as long as the thorax. Pores large, irregular, roundish.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.12; breadth, _a_ 0.04, _b_ 0.08, _c_ 0.16.

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

9. _Lithochytris pteropus_, n. sp. (Pl. 67, fig. 15).

Shell three-sided pyramidal, with two indistinct strictures, but with two broad, internal girdles. Length of the three joints = 2 : 2 : 6, breadth = 2 : 3 : 9. Cephalis with a small horn of half the {1365}length, pear-shaped. Thorax broader than long. Abdomen with three prominent, rounded edges, prolonged over the concave base into three conical, hollow, and fenestrated feet, twice as long as the thorax. Pores small, circular, irregular, in longitudinal series along the edges.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.04, _c_ 0.12; breadth, _a_ 0.04, _b_ 0.06, _c_ 0.18.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

10. _Lithochytris vespertilio_, Ehrenberg.

_Lithochytris vespertilio_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 76, Taf. iv. fig. 10.

Shell three-sided pyramidal, with two indistinct strictures. Length of the three joints = 1 : 2 : 5, breadth = 2 : 3 : 10. Cephalis with a short horn of half the length, conical. Thorax inflated. Abdomen without prominent edges, divided in the lower half into three large, conical, hollow, and fenestrated feet, twice as long as the thorax. Pores small, irregular, roundish.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.1; breadth, _a_ 0.04, _b_ 0.06, _c_ 0.2.

_Habitat._--Fossil in Barbados.

Family LXVI. #PHORMOCYRTIDA#, n. fam.

_Theophormida et Theophænida_, Haeckel, 1881, Prodromus, pp. 436, 437.

_Definition._--#Tricyrtida# multiradiata. (#Cyrtoidea# with a three-jointed shell, divided by two transverse constrictions into cephalis, thorax, and abdomen, with numerous, four to nine or more, radial apophyses.)

The family #Phormocyrtida#, composed of the Theophormida and Theophænida of my Prodromus, comprises those #Cyrtoidea# in which the lattice-shell is three-jointed, and bears numerous radial appendages (usually six or nine, sometimes more, rarely less, four or five). The two subfamilies differ in the shape of the terminal mouth, which is in the Theophormida a simple wide opening, in the Theophænida closed by a lattice-plate. The phylogenetic origin of the Phormocyrtida may be found either in the Podocyrtida or in the Anthocyrtida; they may be derived either from the former by interpolation of interradial, secondary apophyses between the three primary perradial apophyses; or from the latter by development of an abdomen.

The radial apophyses are originally radial ribs, which arise from the base of the cephalis on the collar stricture, run along the thorax and abdomen, and are often prolonged into terminal feet. Whilst in some forms the radial ribs are completely preserved in both joints, they are in other forms only partly visible (in the abdomen), and very often only their free terminal prolongations are preserved in the form of a corona of feet around the mouth of the thorax. This corona is either simple or double. Sometimes also a corona is developed on the lumbar stricture, between the thorax and abdomen.

{1366}These apophyses exhibit a remarkable variety in the great subfamily Theophormida, with open mouth. In the small subfamily Theophænida, however, the apophyses appear as six or nine simple lateral wings on the abdomen.

The Theophormida are richly represented not only in the present seas, but also as fossils in Barbados, and numerous remarkable forms have been already described by Ehrenberg, in his genera _Calocyclas_ and _Cycladophora_. Many Phormocyrtida belong to the most elegant and admirable forms of Radiolaria.

_Synopsis of the Genera of Phormocyrtida._

-------------------------------------------------------------------------
I. Subfamily Theophormida.
Terminal mouth of the abdomen a simple wide opening.
--------------------
Radial ribs enclosed in the wall of the shell, either the thorax
or the abdomen.
-------------------------------------------------------------------------
{ Abdomen flat, dilated, with
{ a wide open mouth, 601. _Theophormis_.
Radial ribs in {
the thorax and {
the abdomen. { Abdomen ovate or cylindrical,
{ with constricted
{ mouth, 602. _Phormocyrtis_

{ Peristome with free terminal
Radial ribs in { feet, 603. _Alacorys_.
the abdomen {
only. { Peristome smooth, without
{ free feet, 604. _Cycladophora_.
-------------------------------------------------------------------------
No radial ribs in the shell wall. Peristome with a corona of
terminal feet.
-------------------------------------------------------------------------
{ Abdomen cylindrical or
Terminal { ovate, not dilated, 605. _Calocyclas_.
corona simple. {
{ Abdomen dilated, truncate,
{ conical or discoidal, 606. _Clathrocyclas_.

{ Both coronas terminal, 607. _Lamprocyclas_.
Corona of feet {
double. { One corona, terminal, the
{ other lumbar, 608. _Diplocyclas_.
-------------------------------------------------------------------------
II. Subfamily Theophænida.
-------------------------------------------------------------------------
Terminal mouth of the { Six lateral wings, 609. _Hexalatractus_.
abdomen closed by a {
lattice-plate. { Nine Lateral wings, 610. _Theophæna_.

Subfamily 1. THEOPHORMIDA, Haeckel, 1881, Prodromus, p. 436.

_Definition._--#Phormocyrtida# with the basal mouth of the shell open (vel Tricyrtida multiradiata aperta).

Genus 601. _Theophormis_,[218] Haeckel, 1881, Prodromus, p. 436.

_Definition._--#Theophormida# (vel Tricyrtida multiradiata aperta) with numerous radial ribs enclosed in the wall of the thorax and of the flat dilated abdomen; mouth of the latter wide open.

{1367}The genus _Theophormis_ commences the series of the Theophormida, or the multiradiate Podocyrtida, as their oldest and simplest form. The three-jointed shell is flat, campanulate or hat-shaped, and pierced by four or more radial ribs, four of which are primary or perradial, the others secondary or interradial. _Theophormis_ may be derived from the similar _Sethophormis_ by development of a lumbar constriction, and a third joint or abdomen.

1. _Theophormis callipilium_, n. sp. (Pl. 70, figs. 1-3).

Shell flat, hat-shaped, with two sharp annular strictures. Cephalis large, flatly cap-shaped, with small, irregular, square meshes (fig. 3). The collar septum (fig. 2) is composed (as in the following species) of four crossed, thin, horizontal beams, each of which is inserted at the collar stricture by a three forked branch. From the centre of the collar stricture (in the common nodal point of the four beams) there arises a vertical, axial rod, which is inserted at the flat top of the cephalis by five branches (one central and four lateral). Length of the three joints = 1 : 3 : 2, breadth = 2 : 6 : 11. Thorax flat, campanulate, with four primary perradial ribs (prolongations of the four cortinar beams), and numerous (twenty to thirty) interpolated secondary ribs; four of these are in interradial (midway between the four primary ribs), and bisect the four large, semicircular, perradial meshes at the base of the thorax. Network of the thorax and abdomen subregular, with hexagonal meshes and thin bars. Abdomen flatly expanded, somewhat curved, like the brim of a hat, half as broad in the anterior (frontal) part as in the posterior (occipital) part, which is about as broad as the radius of the thorax. The twenty to thirty radial ribs of the abdomen are prolongations of the thoracic ribs, and are somewhat prominent at the margin of the peristome, which appears therefore elegantly indented.

_Dimensions._--Length of the three joints, _a_ 0.02 to 0.03, _b_ 0.06 to 0.08, _c_ 0.03 to 0.06; breadth, _a_ 0.05 to 0.08, _b_ 0.2 to 0.3, _c_ 0.4 to 0.5.

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

2. _Theophormis medusa_, n. sp.

Shell flatly campanulate, with two distinct, annular strictures. Length of the three joints = 1 : 2 : 1, breadth = 2 : 5 : 8. Cephalis large, hemispherical. Thorax flatly conical, with four crossed ribs, opposite in pairs in two meridional planes, perpendicular one to another, and prolonged into the flat, nearly discoidal abdomen, which is half as broad as the thorax. The wall of the abdomen is pierced by eight radial ribs; four secondary ribs being interpolated between the four primary. Network of the entire shell very delicate, with regular, hexagonal meshes, and very thin bars. Peristome circular, not dentate.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.07, _c_ 0.04; breadth, _a_ 0.06, _b_ 0.16, _c_ 0.24.

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

3. _Theophormis cruciata_, n. sp.

Shell flat, campanulate, with two distinct annular strictures. Cephalis flat, cap-shaped, with irregular, square meshes. Thorax flat, conical, with hexagonal meshes. Abdomen flatly expanded, {1368}of half the breadth, with larger hexagonal meshes. Thorax and abdomen pierced by four stout radial ribs, lying opposite in pairs in two diameters, perpendicular one to another. No secondary or interradial ribs are interpolated between the four primary. Mouth truncate, circular.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.04; breadth, _a_ 0.05, _b_ 0.18, _c_ 0.25.

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

4. _Theophormis senaria_, n. sp.

Shell flat, hat-shaped, similar to _Theophormis callipilium_ (Pl. 70, figs. 1-3), but with a different number and arrangement of the piercing radial ribs. The cephalis and its collar septum exhibit the same formation as in _Sethophormis hexalactis_, described above (p. 1245, Pl. 56, fig. 6.) The caudal and sternal ribs, which are opposed in the sagittal plane, are simple, whilst the two lateral ribs are forked. In the flat abdomen there are six secondary or interradial ribs, interpolated between the six primary or perradial ribs of the thorax. Delicate network with regular, hexagonal meshes.

_Dimensions._--Length of the three joints, _a_ 0.035, _b_ 0.075, _c_ 0.025; breadth, _a_ 0.07, _b_ 0.2, _c_ 0.3.

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

Genus 602. _Phormocyrtis_,[219] n. gen.

_Definition._--#Theophormida# (vel Tricyrtida multiradiata aperta) with numerous radial ribs enclosed in the wall of the thorax, and of the ovate or cylindrical abdomen; mouth of the latter constricted.

The genus _Phormocyrtis_ differs from the preceding _Theophormis_ in the ovate or cylindrical form of the abdomen, the mouth of which is more or less constricted. The former exhibits, therefore, the same relation to the latter that _Sethamphora_ bears to _Sethophormis_ among the Dicyrtida. _Phormocyrtis_ may be derived directly either from _Sethamphora_ by development of an abdomen, or from _Pterocorys_ or _Theopilium_ by multiplication of the three radial ribs.

1. _Phormocyrtis carinata_, n. sp.

Shell ovate, with two slight strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 3 : 4. Cephalis hemispherical, with a stout pyramidal horn of twice the length, and few very small pores. Pores in the campanulate thorax and the inflated abdomen regular, circular, small, and numerous. Six stout prominent ribs, beginning from the collar stricture, arise along the thorax and abdomen, and reach the constricted mouth, which is half as broad as the abdomen. (This species is very similar to _Pterocorys carinata_, from which it differs in the six complete radial ribs of the shell-wall.)

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.06, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.12.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

{1369}2. _Phormocyrtis fastosa_, Haeckel.

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

Shell ovate, with two distinct strictures. Length of the three joints = 1 : 3 : 3, breadth = 1 : 5 : 6. Cephalis ovate, with a stout pyramidal horn of the same length, and numerous rather large pores. Pores in the campanulate thorax and the inflated abdomen much smaller, very numerous, regular, hexagonal. Along these two joints arise nine delicate, divergent ribs; these extend almost to the wide mouth, which is slightly constricted.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.09, _c_ 0.08; breadth, _a_ 0.02, _b_ 0.1, _c_ 0.12.

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

3. _Phormocyrtis costata_, n. sp. (Pl. 69, fig. 6).

Shell smooth, with sharp collar, but indistinct lumbar stricture. Length of the three joints = 2 : 5 : 5, breadth = 2 : 6 : 6. Cephalis conical, with a stout pyramidal horn of twice the length. Thorax and abdomen together nearly cylindrical, constricted towards both poles, with thirty to forty longitudinal ribs, which are nearly parallel, vertical in the middle part, and convergent towards both poles; alternate with the same number of longitudinal rows of regular, circular pores. Mouth with a broad, hyaline, only slightly constricted peristome.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.1, _c_ 0.1; breadth, _a_ 0.04, _b_ 0.12, _c_ 0.12.

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

4. _Phormocyrtis embolum_, Haeckel.

_Eucyrtidium embolum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 70, Taf. x. fig. 5.

Shell smooth, with sharp collar, but indistinct lumbar stricture. Length of the three joints = 3 : 7 : 10, breadth = 3 : 9 : 7. Cephalis subspherical, with a pyramidal horn of the same length. Thorax campanulate; abdomen inversely truncate, conical; both with sixteen to twenty longitudinal ribs, and alternate longitudinal rows of small circular pores, converging towards the two poles. Mouth truncate, with broad hyaline peristome.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.07, _c_ 0.1; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.07.

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

5. _Phormocyrtis quadrata_, n. sp.

Shell ovate, papillate, with two slight strictures. Length of the three joints = 2 : 3 : 13, breadth = 4 : 6 : 11. Cephalis hemispherical, small, with two divergent, pyramidal horns of twice the length. Along the hemispherical thorax and the ovate inflated abdomen run twenty-four to thirty curved ribs, converging towards the two poles, and alternate with the same number of {1370}longitudinal rows of circular, regular pores, disposed in ten to twelve transverse rows. Each pore with a square, elevated frame. Mouth constricted, only one-third as broad as the thorax.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.03, _c_ 0.13; breadth, _a_ 0.04, _b_ 0.06, _c_ 0.11.

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

6. _Phormocyrtis longicornis_, n. sp. (Pl. 69, fig. 15).

_Theocorys longicornis_, Haeckel, 1881, Prodromus et Atlas, _loc. cit._

Shell slender, ovate, rough, with two slight strictures. Length of the three joints = 3 : 8 : 12, breadth = 4 : 10 : 11. Cephalis hemispherical, with a very large, cylindrical horn, about as long as the shell. Thorax hemispherical, with regular, circular, hexagonally-framed pores. Abdomen subcylindrical, with twenty to twenty-four nearly parallel undulate ribs, and alternate longitudinal rows of regular, circular pores. Mouth constricted, circular, about half as broad as the thorax.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.08, _c_ 0.12; breadth, _a_ 0.04, _b_ 0.1, _c_ 0.11.

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

Genus 603. _Alacorys_,[220] Haeckel, 1881, Prodromus, p. 436.

_Definition._--#Theophormida# (vel Tricyrtida multiradiata aperta) with numerous radial ribs in the abdomen, which are prolonged over the mouth into free feet.

The genus _Alacorys_ and the following _Cycladophora_ differ from the preceding two genera in the formation of the radial ribs, which arise from the lumbar stricture, and lie in the wall of the abdomen, but are absent on the thorax. The shell is usually large, more or less pyramidal or conical, with a wide open terminal mouth. The latter is in _Cycladophora_ simply truncate, whilst in _Alacorys_ it is surrounded by from four to twelve or more terminal feet, prolongations of the abdominal ribs. According to the different number of these (four, five, six, or more) some subgenera may be distinguished, as _Tetralacorys_, _Pentalacorys_, _Hexalacorys_, &c.

Subgenus 1. _Tetralacorys_, Haeckel, 1881, Prodromus, p. 436.

_Definition._--Peristome armed with four feet, opposite in two meridian planes, which are perpendicular to one another.

1. _Alacorys lutheri_, n. sp. (Pl. 65, fig. 4).

Shell papillate, with distinct collar stricture. Length of the three joints = 3 : 6 : 6, breadth = 3 : 8 : 10. Cephalis subspherical, with a pyramidal horn of the same length. Thorax tuberculate, {1371}nearly hemispherical, with circular pores of very different sizes. From the margin of its wide open mouth descend four stout perradial ribs, which are forked at the distal end, and by communication of their fork-branches form the four large, pentagonal holes of the abdomen. From the middle of the lower margin of the holes descend four parallel, vertical, slender feet, about as long as the shell. This species is dedicated to the memory of the great Reformer, Martin Luther.

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

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

2. _Alacorys tetracantha_, Haeckel.

_Podocyrtis tetracantha_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 82, Taf. xiii. fig. 2.

? _Podocyrtis parvipes_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 82, Taf. xiv. fig. 5.

Shell rough, with distinct collar stricture. Length of the three joints = 1 : 3 : 5, breadth = 1 : 4 : 6. Cephalis subspherical, with a rudimentary conical horn. Thorax campanulate, with irregular, roundish pores of different sizes. Abdomen inflated, with a small number of very large irregular holes, intermingled with smaller roundish holes. From the margin of the wide open mouth descend, nearly vertically, four strong vertical feet, which are about as long as the shell, and slightly curved, with convex outlines. _Podocyrtis parvipes_ of Ehrenberg seems to be only a mutilated specimen of this species.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.13.

_Habitat._--Fossil in Barbados.

Subgenus 2. _Pentalacorys_, Haeckel, 1881, Prodromus, p. 436.

_Definition._--Peristome armed with five feet, one of which is odd and occipital, the other four paired and lateral.

3. _Alacorys pentacantha_, Haeckel.

_Podocyrtis pentacantha_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 82, Taf. xvii. fig. 1.

Shell rough, with slight collar stricture. Length of the three joints = 1 : 2 : 3, breadth = 1 : 4 : 6. Cephalis subspherical, with a rudimentary conical horn. Thorax campanulate, with subregular, circular, quincuncial pores. Abdomen wider, campanulate, with a small number of very large and irregular, roundish holes. From the peristome descend five stout conical feet, which are slightly curved and divergent, nearly as long as the shell.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.06; breadth, _a_ 0.025, _b_ 0.08, _c_ 0.11.

_Habitat._--Fossil in Barbados.

{1372}4. _Alacorys bismarckii_, n. sp. (Pl. 65, fig. 3).

Shell spiny, with distinct collar stricture. Length of the three joints = 1 : 4 : 5, breadth = 2 : 7 : 10. Cephalis hemispherical, with a very stout, dimpled, conical horn of the same length. Thorax campanulate, spiny, with regular, circular pores. Abdomen wider, campanulate, with larger conical spines, and a small number of irregular, roundish, very large holes. From the peristome descend, nearly vertically, five very large cylindrical feet, nearly twice as long as the shell; they are S-shaped, curved, spinulate in the distal half, and armed at the proximal base with two stout conical spines, the smaller of which is directed inwards, the larger curved upwards. Dedicated to Prince Otto von Bismarck, the Reconstructor of the German Empire.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.1; breadth, _a_ 0.04, _b_ 0.14, _c_ 0.2.

_Habitat._--Western Tropical Pacific (north of New Guinea), Station 220, depth 1100 fathoms.

Subgenus 3. _Hexalacorys_, Haeckel, 1881, Prodromus, p. 436.

_Definition._--Peristome armed with six feet, three of which are primary or perradial (Podocyrtis), the three other alternate, secondary or interradial.

5. _Alacorys friderici_, n. sp. (Pl. 65, fig. 1).

Shell conical, rough, with sharp collar stricture. Cephalis subspherical, with a large, oblique, prismatic horn, twice the length. Thorax campanulate, with regular, circular pores (six to eight in its length). Abdomen wider, campanulate, with a small number of very large pores (three to four in the course of its length). Peristome with six very large divergent feet, which are about as long as the shell, cylindrical, irregularly curved. The specimen figured was observed living, with expanded pseudopodia. The central capsule exhibited four large pear-shaped lobes, filling up the shell-cavity; each contained an oil-globule in the thoracic part. The undivided cephalic part of the capsule enclosed a nucleus, from which four lobes protruded through the four collar pores into the thorax. Dedicated to Frederick the Great, the Royal Philosopher of Potsdam.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.06, _c_ 0.08; breadth, _a_ 0.04, _b_ 0.09, _c_ 0.14.

_Habitat._--North Atlantic, Canary Islands, Lanzerote (Haeckel), surface.

6. _Alacorys guilelmi_, n. sp. (Pl. 65, fig. 2).

Shell thorny, with distinct collar stricture. Length of the three joints = 1 : 3 : 4, breadth = 2 : 5 : 8. Cephalis hemispherical, with a rudimentary conical horn. Thorax hemispherical, spiny, with regular, circular pores. Abdomen wider, campanulate, papillate, with a small number of very large circular holes. Peristome with six diverging feet, which are about as long as the shell, at the base conical, thickened, and at the distal end curved inwards, with a spinulate knob. Dedicated to the German Emperor, Wilhelm.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.08; breadth, _a_ 0.03, _b_ 0.1, _c_ 0.16.

_Habitat._--Western Tropical Pacific, Station 224, depth 1850 fathoms.

{1373}7. _Alacorys hexacantha_, n. sp.

Shell thorny, with slight collar stricture. Length of the three joints = 2 : 5 : 7, breadth = 4 : 10 : 14. Cephalis flat, cap-shaped, with a rudimentary conical horn. Thorax campanulate, with regular, circular pores. Abdomen wider, campanulate, with a small number of very large polygonal pores. Peristome with six large divergent feet, which are longer than the shell, cylindrical, and slightly curved, in the proximal half convex, in the distal half concave.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.07; breadth, _a_ 0.04, _b_ 0.1, _c_ 0.14.

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

8. _Alacorys hexapleura_, n. sp.

Shell spiny, with distinct collar stricture. Length of the three joints = 2 : 10 : 8, breadth = 3 : 11 : 10. Cephalis hemispherical, large, hyaline, and thick-walled, with a very stout, conical horn of the same length. Thorax pear-shaped, with numerous, regular, circular pores and conical spines, the size of which increases gradually towards the deep, lumbar stricture. Abdomen truncate, conical, with irregular, roundish pores, and six very strong, straight, divergent ribs, prolonged into six short, conical feet.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.2, _c_ 0.16; breadth, _a_ 0.06, _b_ 0.22, _c_ 0.2.

_Habitat._--Fossil in Barbados.

Subgenus 4. _Octalacorys_, Haeckel.

_Definition._--Peristome armed with eight feet, four of which are primary or perradial (corresponding to those of _Tetralacorys_), the other four alternate, secondary, or interradial.

9. _Alacorys aculeata_, Haeckel.

_Podocyrtis aculeata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 80, Taf. xiii. fig. 3.

_Podocyrtis aculeata_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol.
xxxvi. p. 540, Taf. xxxiii. fig. 34.

Shell spiny, with deep collar stricture. Length of the three joints = 2 : 5 : 8, breadth = 2 : 7 : 10. Cephalis subspherical, with a slender, conical horn of twice the length. Thorax campanulate, thorny, with regular, circular pores. Abdomen wider, campanulate, with a small number of very large, regular, hexagonal meshes, and stout spines in the nodal points. Peristome with eight strong conical feet, which are nearly parallel, little curved (convex at the outside), and sometimes all of the same size (equal to the length of the shell); at other times different, four larger alternating with four smaller feet.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.05, _c_ 0.08; breadth, _a_ 0.025, _b_ 0.07, _c_ 0.1.

_Habitat._--Fossil in Barbados.

{1374}10. _Alacorys octacantha_, n. sp.

Shell spiny, with deep collar stricture. Length of the three joints = 2 : 8 : 6, breadth = 3 : 7 : 7. Cephalis ovate, with a short, conical horn. Thorax pear-shaped, spiny, with regular, circular pores, similar to _Cycladophora erinaceus_, Ehrenberg (1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xviii. fig. 2). Abdomen truncate, conical, with irregular, roundish pores, and eight stout, straight, thorny, divergent ribs of equal size, which are prolonged into eight free, conical, spiny feet of the same length.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.16. _c_ 0.12; breadth, _a_ 0.06, _b_ 0.14, _c_ 0.14.

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

Subgenus 5. _Ennealacorys_, Haeckel.

_Definition._--Peristome armed with nine feet, three of which are primary or perradial, the other six secondary or interradial.

11. _Alacorys enneacantha_, n. sp.

Shell papillate, with slight collar stricture. Length of the three joints = 2 : 4 : 8, breadth = 3 : 6 : 9. Cephalis hemispherical, with a stout, conical horn of twice the length. Thorax campanulate, with subregular, circular pores, and small, conical papillæ. Thorax wider, campanulate, with circular pores, and conical papillæ of three times the size. Peristome with nine widely divergent, little curved, conical feet, about as long as the shell. Similar to _Podocyrtis ventricosa_, Ehrenberg (1875, _loc. cit._, Taf. xvi. fig. 3), different mainly in the feet.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.08; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.09.

_Habitat._--Central Pacific, Station 268, depth 2900 fathoms.

12. _Alacorys gigas_, n. sp.

Shell thorny, with distinct collar stricture. Length of the three joints = 1 : 4 : 2, breadth = 1 : 5 : 4. Cephalis ovate, with a short, conical horn of about half the length. Thorax campanulate, thorny, with small, regular, circular pores, very similar to _Cycladophora gigas_, Ehrenberg (_loc. cit._, 1875, p. 68, Taf. xviii. fig. 1). Abdomen truncate, conical, smooth, with irregular, roundish pores, and nine stout and straight, little divergent ribs, which are prolonged into nine cylindrical, pointed feet of the same length.

_Dimensions._--Length of the three joints, _a_ 0.05, _b_ 0.2, _c_ 0.1; breadth, _a_ 0.05, _b_ 0.25, _c_ 0.2.

_Habitat._--Fossil in Barbados.

Subgenus 6. _Polyalacorys_, Haeckel.

_Definition._--Peristome with numerous (ten to twenty or more) prominent feet, three or four of which are primary and perradial, the others secondary and interradial.

{1375}13. _Alacorys dodecantha_, n. sp.

? _Podocyrtis schomburgkii_, var., Bury, 1862, Polycystins of Barbados,
Taf. xii. fig. 3.

Shell smooth, with slight collar stricture. Length of the three joints = 1 : 3 : 4, breadth = 1 : 4 : 7. Cephalis ovate, with a conical horn of the same length. Thorax campanulate, with regular, circular pores. From its margin arise twelve stout, little curved, radial beams, which are widely divergent, and connected in the middle part by a transverse circular ring, so that the abdomen exhibits twelve large triangular holes, and at the peristome, alternating with these, twelve free conical feet of the same length.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.09, _c_ 0.11; breadth, _a_ 0.03, _b_ 0.12, _c_ 0.22.

_Habitat._--Central Pacific, Station 263, depth 2650 fathoms; also fossil in Barbados.

14. _Alacorys carcinus_, n. sp. (Pl. 74, fig. 9).

_Calocyclas carcinus_, Haeckel, 1879, Atlas, _loc. cit._

_Podocyrtis schomburgkii_, var., Bury, 1862, Polycystins of Barbados, pl.
i. fig. 2; pl. xii. fig. 4.

Shell rough, with distinct collar stricture. Length of the three joints = 1 : 4 : 4, breadth = 2 : 6 : 6. Cephalis hemispherical, with a large, cylindrical, bent spine of three times the length. Thorax inflated, campanulate, with large, regular, circular pores. Abdomen truncate, conical, with three to four transverse rows of regular, square pores, produced by eighteen divergent, straight ribs, which are connected by three to four horizontal rings. Distal end of the ribs prolonged into eighteen slender, conical feet, which are about as long as the thorax and slightly curved inwards.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.08; breadth, _a_ 0.05, _b_ 0.12, _c_ 0.12.

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

15. _Alacorys polyacantha_, n. sp.

Shell spiny, with deep collar stricture. Length of the three joints = 3 : 9 : 10, breadth = 4 : 12 : 16. Cephalis hemispherical, with a stout conical horn of the same length. Thorax campanulate, with regular, circular pores and conical spines, increasing in size towards the deep lumbar stricture. Abdomen truncate, conical, with twenty to thirty divergent, straight ribs, which are connected by four to six transverse rings, and prolonged into free conical feet of half the length. Therefore four to six transverse rings of regular, square pores occur.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.09, _c_ 0.1; breadth, _a_ 0.04, _b_ 0.12, _c_ 0.16.

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

16. _Alacorys ornata_, Haeckel.

_Cryptoprora ornata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. v. fig. 8.

Shell ovate, smooth, without external strictures, but with two internal annular septa. Length of the three joints = 3 : 5 : 4, breadth = 3 : 6 : 5. Cephalis subspherical, partly enclosed by the uppermost part of the thorax, without horn, or with a small rudimentary horn. Pores subregular, {1376}circular, half as broad in the cephalis as in the two other joints. Thorax campanulate. Abdomen truncate, with eighteen to twenty-four parallel, vertical, longitudinal ribs, which are prolonged into slender, free, conical feet of the same length. (This remarkable species may be derived from _Carpocanium_ by apposition of a third joint.)

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

_Habitat._--Fossil in Barbados.

Genus 604. _Cycladophora_,[221] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Theophormida# (vel Tricyrtida multiradiata aperta) with four to six or more radial ribs in the abdomen, the terminal mouth of which is truncate, without feet.

The genus _Cycladophora_ differs from the preceding _Alacorys_, its probable ancestral genus, in the absence of free terminal feet, the radial ribs of the abdomen being connected by transverse beams throughout their whole length. The number of the regularly disposed ribs (four to six or more) may also here be used for the distinction of different subgenera.

Subgenus 1. _Lampterium_, Haeckel, 1881, Prodromus, p. 434.

_Definition._--Abdomen with four radial ribs, opposite in pairs in two meridian planes, perpendicular one to another.

1. _Cycladophora goetheana_, n. sp. (Pl. 65, fig. 5).

Shell shaped like a lantern, with two sharp strictures. Length of the three joints = 1 : 2 : 12, breadth = 1 : 4 : 7. Cephalis hemispherical, with a slender pyramidal horn of three times the length. Thorax twice as large, thorny, hemispherical, with regular, circular pores. Abdomen very long, nearly four-sided prismatic, with four superior smaller, and four inferior larger holes; the former separated by four short, divergent, perradial, the latter by four long, parallel, vertical, interradial bars. Mouth square, four-lobed. Dedicated to Wolfgang Goethe.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.24; breadth, _a_ 0.03, _b_ 0.07, _c_ 0.1 to 0.14.

_Habitat._--Central Pacific, Stations 265 to 269, depth 2550 to 2900 fathoms.

2. _Cycladophora tetrapleura_, n. sp.

Shell very similar to the preceding species, but differing in the following characters: Cephalis conical, with a horn of the same length. Thorax campanulate. Four ribs of the abdomen not {1377}parallel and vertical, but more or less divergent. Length of the three joints = 1 : 2 : 8, breadth = 1 : 2 : 4. Whole shell slender, pyramidal. Mouth square, four-lobed.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.06, _c_ 0.24; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.12.

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

3. _Cycladophora lanterna_, n. sp.

Shell very similar to the two preceding species, but differing in the following characters. Cephalis subspherical, with a thick, pyramidal horn of the same breadth, and three times the length. Thorax hemispherical, with circular, hexagonally-framed pores. Abdomen ovate, with four convex ribs, and twelve large holes, four superior smaller pentagonal, four intermediate very large, ovate, and four inferior, small, triangular holes. Mouth little constricted, nearly circular.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.05, _c_ 0.22; breadth, _a_ 0.025, _b_ 0.08, _c_ 0.11.

_Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms.

Subgenus 2. _Lamptidium_, Haeckel.

_Definition._--Abdomen with six radial ribs (three primary or perradial, and three alternate, secondary or interradial).

4. _Cycladophora hexapleura_, n. sp.

_Lanterna chinensis_, Bury, 1862, Polycystins of Barbados, pl. xiii. fig.
7.

Shell shaped like a lantern, with six sides and two sharp strictures. Length of the three joints = 1 : 2 : 8, breadth = 1 : 2 : 4. Cephalis hemispherical, with a conical spine of the same length. Thorax twice as large, hemispherical, with regular, circular pores. Abdomen nearly six-sided prismatic, with six descending, little curved ribs, and eighteen large holes between them; six superior holes interradial, ovate, six intermediate holes very large, perradial, ovate, six inferior holes triangular, interradial. Mouth six-lobed.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.16; breadth, _a_ 0.03, _b_ 0.06, _c_ 0.1.

_Habitat._--Fossil in Barbados.

5. _Cycladophora pyramidalis_, n. sp.

_Podocyrtis_ sp., Bury, 1862, Polycystins of Barbados, pl. xii. fig. 2.

Shell slender, pyramidal, with six sides and two slight strictures. Length of the three joints = 1 : 4 : 12, breadth = 1 : 4 : 8. Cephalis subspherical, with a conical horn of twice the length. Thorax conical, with regular, circular pores. Abdomen truncate, pyramidal, with six strong, divergent, straight ribs, which are connected by five to six transverse, hexagonal rings; therefore {1378}six longitudinal rows of large, roundish, quadrangular meshes (four to five meshes in each row). Mouth hexagonal.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.1, _c_ 0.3; breadth, _a_ 0.03, _b_ 0.1, _c_ 0.2.

_Habitat._--Fossil in Barbados.

6. _Cycladophora spinosa_, n. sp.

Shell spiny, with two deep strictures. Length of the three joints = 1 : 4 : 3, breadth = 1 : 5 : 4. Cephalis subspherical, with a stout conical horn of the same length. Thorax ovate, with regular, circular pores, and numerous conical spines. Abdomen truncate, conical, with irregular, roundish pores, and six strong, divergent ribs. Mouth circular.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.12, _c_ 0.09; breadth, _a_ 0.03, _b_ 0.15, _c_ 0.12.

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

Subgenus 3. _Lamptonium_, Haeckel.

_Definition._--Abdomen with nine radial ribs (three primary or perradial, and six secondary or interradial).

7. _Cycladophora enneapleura_, n. sp.

Shell spiny, with two sharp strictures. Length of the three joints = 1 : 5 : 3, breadth = 2 : 7 : 4. Cephalis hemispherical, with a conical horn of twice the length. Thorax campanulate, with regular, circular pores, and conical thorax. Abdomen cylindrical, with nine straight, parallel ribs, and irregular, roundish pores. Mouth circular. (_Similar to Cycladophora gigas_, Ehrenberg, 1875, _loc. cit._, Taf. xviii. fig. 1, but differing in the possession of nine abdominal ribs.)

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.15, _c_ 0.1; breadth, _a_ 0.06, _b_ 0.2, _c_ 0.12.

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

8. _Cycladophora nonagona_, n. sp.

Shell spiny, with two distinct strictures. Length of the three joints = 3 : 10 : 7, breadth = 2 : 9 : 8. Cephalis pear-shaped, with a stout pyramidal horn of the same length. Thorax pear-shaped, with regular, circular pores, and conical horns, increasing in size towards the base. Abdomen truncate, pyramidal, with nine straight, spinulate ribs, and nine even faces between them, with irregular, roundish pores. Mouth nonagonal.

_Dimensions._--Length of the three joints, _a_ 0.06, _b_ 0.2, _c_ 0.14; breadth, _a_ 0.05, _b_ 0.18, _c_ 0.16.

_Habitat._--Fossil in Barbados.

{1379}Subgenus 4. _Cyclampterium_, Haeckel.

_Definition._--Abdomen truncate, conical or campanulate, with numerous (ten to twenty or more) divergent ribs. Mouth wide open, truncate.

9. _Cycladophora pantheon_, n. sp. (Pl. 68, fig. 3).