Chapter XX: Section III: TRICYRTIDA, Haeckel, 1881, Prodromus, p. 426, 434 (1)

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

_Synopsis of the Families and Subfamilies of Tricyrtida._

Family LXV. Podocyrtida. { Mouth open, Theopilida.
Three radial apophyses. {
{ Mouth closed, Theoperida.

Family LXVI. Phormocyrtida. { Mouth open, Theophormida.
Numerous radial apophyses. {
{ Mouth closed, Theophænida.

Family LXVII. Theocyrtida. { Mouth open, Theocorida.
No radial apophyses. {
{ Mouth closed, Theocapsida.

{1314}Family LXV. #PODOCYRTIDA#, n. fam. (Pl. 67, 68, 71-73).

_Theopilida et Theoperida_, Haeckel, 1881, Prodromus, p. 435, 436.

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

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

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

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

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

{1315}_Synopsis of the Genera of Podocyrtida._

-------------------------------------------------------------------------
I. Subfamily Theopilida. (Podocyrtida aperta.)
Terminal mouth of the shell a simple wide opening.
--------------------
A. Three free limbs or wings on the thorax (partly also on the abdomen).
-------------------------------------------------------------------------
{ { Wings arising from
{ { the thorax, 582. _Pterocorys_.
{ {
{ Three wings of { Three ribs enclosed
{ the thorax { in the wall of the
{ solid. { thorax, 583. _Theopilium_.
No free { {
external { { Wings arising free
appendages{ { from the collar
on the { { stricture, 584. _Corocalyptra_.
abdomen. {
{ { Wings not prolonged
{ Three wings of { into the cephalis, 585. _Dictyoceras_.
{ the thorax {
{ latticed. { Wings prolonged
{ { into the cephalis, 586. _Pteropilium_.

{ Three ribs { Ribs and feet
{ prolonged { solid, 587. _Theopodium_.
{ into three {
{ terminal { Ribs and feet
Free { feet. { latticed, 588. _Pterocanium_.
appendages{
on the { Three free { Wings and feet
abdomen. { wings on the { solid, 589. _Pterocodon_.
{ thorax. {
{ Numerous { Wings and feet
{ terminal feet. { latticed, 590. _Dictyocodon_.

-------------------------------------------------------------------------
B. Free appendages not on the thorax, only on the abdomen.
-------------------------------------------------------------------------
Abdomen with three ribs and three feet, 591. _Pleuropodium_.

{ Three feet solid,
{ simple, 592. _Podocyrtis_.
Abdomen without lateral {
ribs, with three { Three feet solid,
terminal feet. { ramified, 593. _Thyrsocyrtis_.
{
{ Three feet latticed, 594. _Dictyopodium_.
-------------------------------------------------------------------------
II. Subfamily Theoperida. (Podocyrtida clausa.)
Terminal mouth of the shell closed by a lattice-plate.
--------------------
Three lateral wings only on the thorax,
-------------------------------------------------------------------------
Wings solid, 595. _Lithornithium_.

Wings latticed, 596. _Sethornithium_.
-------------------------------------------------------------------------
Three lateral wings beginning from the thorax and prolonged
into the abdomen,
-------------------------------------------------------------------------
597. _Theopera_.
-------------------------------------------------------------------------
Three wings only on the abdomen.
-------------------------------------------------------------------------
{ No horn on the
{ basal pole, 598. _Rhopalocanium_.
Spell spindle-shaped, with {
three lateral wings on the { Basal pole of the
abdomen. { shell with a horn, 599. _Rhopalatractus_.

Shell three-sided pyramidal, with three
terminal-feet on the basal corners, 600. _Lithochytris_.

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

_Definition._--#Podocyrtida# with the terminal mouth of the shell open (vel Tricyrtida triradiata aperta).

{1316}Genus 582. _Pterocorys_,[199] Haeckel, 1881, Prodromus, p. 435.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three simple, free lateral wings arising from the sides of the thorax.

The genus _Pterocorys_, comprising numerous and some very common species, may be one of the oldest and most primitive Theopilida, and is perhaps the common ancestral form of all Tricyrtida. It exhibits three free lateral wings, arising from the sides of the thorax, like _Lithomelissa_ among the Dicyrtida, and may be derived directly from this genus by development of an abdomen. The latter is commonly cylindrical or ovate, with a wide open mouth, whilst the thorax is either campanulate or three-sided and pyramidal.

Subgenus 1. _Pterocyrtidium_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 531.

_Definition._--Horn of the cephalis simple. Abdomen not prolonged into a narrow tube.

1. _Pterocorys campanula_, n. sp. (Pl. 71, fig. 3).

Shell campanulate, with two distinct strictures. Length of the three joints = 2 : 3 : 2, breadth = 2 : 4 : 6. Cephalis subovate, with a pyramidal horn of the same length. Thorax subconical, in the middle zone with three conical, horizontal wings, shorter than the cephalis, from which three thin ribs are decurrent to the mouth. Abdomen short and much dilated, with wide, truncate mouth. Pores nearly equal, small, subregular, circular.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.06, _c_ 0.04; breadth, _a_ 0.03, _b_ 0.08, _c_ 0.12.

_Habitat._--Central Pacific, Stations 266 to 274, surface.

2. _Pterocorys carinata_, Haeckel.

_Eucyrtidium carinatum_, Haeckel, 1862, Monogr. d. Radiol., p. 322, Taf.
vii. figs. 4-7.

Shell subovate, with two distinct strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 3 : 4. Cephalis ovate, with a pyramidal horn of twice the length. Thorax campanulate, with three decurrent crests, from which in the lower part three small conical wings arise, shorter than the cephalis. Abdomen barrel-shaped, inflated, with wide, truncate mouth. Pores everywhere equal, small, regular, circular, quincuncial.

_Dimensions._--Length of the three joints, _a_ 0.25, _b_ 0.05, _c_ 0.075; breadth, _a_ 0.25, _b_ 0.09, _c_ 0.1.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific; many stations, surface.

{1317}3. _Pterocorys sabæ_, Haeckel.

_Pterocanium sabæ_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 299, Taf. x. fig. 17.

Shell campanulate or subconical, with two sharp strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 4 : 5. Cephalis subspherical, with a conical horn of the same length. Thorax subconical, in the lower third with three small, conical, little curved wings, shorter than the cephalis. Abdomen dilated towards the wide, truncate mouth. Pores subregular, circular, gradually increasing in size from the collar towards the mouth.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.06, _c_ 0.08; breadth, _a_ 0.02, _b_ 0.08, _c_ 0.09.

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

4. _Pterocorys columba_, n. sp. (Pl. 71, fig. 2).

Shell subovate, with two deep strictures. Length of the three joints = 2 : 5 : 4, breadth = 3 : 7 : 7. Cephalis hemispherical, with a curved conical horn of the same length. Thorax inflate, in the middle zone with three pyramidal downwardly divergent wings of nearly the same length. Abdomen short, inflate, little constricted towards the wide, truncate mouth. Pores all nearly equal, subregular, circular.

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

_Habitat._--North Pacific, Station 237, surface.

5. _Pterocorys falcifera_, Haeckel.

_Pterocanium falciferum_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 107,
Taf. iv. fig. 15.

? _Pterocanium bibrachiatum_, Stöhr, 1880, Palæontogr., vol xxvi. p. 106,
Taf. iv. fig. 14.

Shell subovate, with two distinct strictures. Length of the three joints = 2 : 6 : 5, breadth = 3 : 9 : 10. Cephalis subspherical, with a conical horn of the same length. Thorax hemispherical, thick-walled, rough, with three stout triangular wings, which are about as long as the shell, and curved downwards, with upper convexity. Abdomen ovate, cylindrical, with wide, truncate mouth. Pores irregular, roundish, large and small intermingled; at the base of the abdomen (below the lumbar girdle) a circle of somewhat oblong, quadrangular pores.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.05; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.1.

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

6. _Pterocorys aquila_, n. sp. (Pl. 71, fig. 5).

Shell ovate, with two deep strictures. Length of the three joints = 1 : 4 : 4, breadth = 1 : 8 : 6. Cephalis hemispherical, with a slender curved horn of three times the length. Thorax hemispherical, campanulate, spiny, prolonged above the lumbar girdle into three stout, three-sided prismatic {1318}wings, which are longer than the shell, fenestrated at the base, and S-shaped, curved. Abdomen barrel-shaped, with wide, truncate mouth. Pores irregular, roundish, of very different sizes.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.08; breadth, _a_ 0.03, _b_ 0.16, _c_ 0.12.

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

7. _Pterocorys hirundo_, n. sp. (Pl. 71, fig. 4).

Shell slender, ovate, with two deep strictures. Length of the three joints = 1 : 4 : 4, breadth = 2 : 5 : 5. Cephalis hemispherical, with a large pyramidal horn longer than the half shell. Thorax conical, spiny, prolonged above the lumbar girdle into three slender, triangular, prismatic wings, which are about as long as the shell, and slightly curved downwards, with lower convexity. Abdomen inflated, with wide, truncate mouth. Pores irregular, roundish, of very different sizes.

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

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

8. _Pterocorys barbadensis_, Haeckel.

_Pterocanium barbadense_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 82, Taf. xvii. fig. 6.

_Pterocyrtidium barbadense_, Bütschli, 1882, Zeitschr. f. wiss. Zool.,
Bd. xxxvi., Taf. xxxiii. fig. 29, _a_, _b_.

Shell slender, smooth, with two slight strictures. Length of the three joints = 1 : 3 : 4, breadth = 2 : 4 : 4. Cephalis hemispherical, with a stout pyramidal horn of twice the length. Thorax campanulate-conical, in the lower half with three divergent, angular wings, which are slightly curved downwards, and as long as the thorax. Abdomen cylindrical, with wide, truncate mouth. Pores small, subregular, circular.

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

_Habitat._--Fossil in Barbados.

9. _Pterocorys apis_, Haeckel.

_Pterocodon apis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin,
p. 82, Taf. xix. fig. 3.

Shell slender, smooth, with two distinct strictures. Length of the three joints = 1 : 2 : 6, breadth = 2 : 3 : 4. Cephalis hemispherical, with a curved, conical horn of three times the length. Thorax very small, with three nearly horizontal, conical wings, which are slightly curved downwards, and twice as long as the thorax. Abdomen cylindrical, three times as long as the thorax, with wide, truncate mouth. Pores small, subregular, circular. Differs from all other species in the very small size of the thorax; the abdomen is broken off in Ehrenberg's figure.

_Dimensions._--Length of the three joints, _a_ 0.15, _b_ 0.02, _c_ 0.06; breadth, _a_ 0.02, _b_ 0.03, _c_ 0.04.

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

{1319}10. _Pterocorys melitta_, Haeckel.

_Rhopalocanium ornatum_, Bury, 1862, Polycystins of Barbados, Taf. vi.
fig. 4.

Shell slender, smooth, with two deep strictures. Length of the three joints = 1 : 1 : 3, breadth = 1 : 2 : 2. Cephalis subspherical, with a pyramidal horn of twice the length. Thorax broad and short, loaf-shaped, with three conical wings, which are horizontally expanded, and half as long as the shell. Abdomen cylindrical, with wide, truncate mouth. Pores small, subregular, circular.

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

_Habitat._--Fossil in Barbados.

11. _Pterocorys turgida_, Haeckel.

_Lychnocanium turgidum_, Ehrenberg, 1885, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 80, Taf. vii. fig. 6.

Shell thick-walled, pear-shaped, smooth, with sharp collar stricture. The lumbar stricture is not distinct externally, but is represented by a broad, internal, annular septum. Length of the three joints = 1 : 6 : 3, breadth = 2 : 7 : 6. Cephalis hemispherical, with a stout pyramidal horn of the same length. Thorax and abdomen together pear-shaped, inflated. Immediately above the lumbar stricture three stout, conical, lateral wings, as long as the cephalis, arise. Mouth very small, about as broad as the cephalis.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.12, _c_ 0.06; breadth, _a_ 0.03, _b_ 0.13, _c_ 0.12.

_Habitat._--Fossil in Barbados.

Subgenus 2. _Pterosyringium_, Haeckel.

_Definition._--Horn of the cephalis simple. Abdomen prolonged into a narrow cylindrical tube.

12. _Pterocorys tubulosa_, n. sp. (Pl. 68, fig. 6).

_Pterosyringium tubulosum_, Haeckel, 1879, Atlas, _loc. cit._

Shell thick-walled, rough, with two slight strictures. Length of the three joints = 1 : 4 : 4, breadth = 1 : 3 : 1. Cephalis hemispherical, with a conical horn of the same length. Thorax ovate, in the upper half with three ribs, arising into short, triangular, slightly prominent wings. Abdomen prolonged into a cylindrical, narrow tube of the same length as the thorax. Terminal mouth very narrow. Pores subregular, circular.

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

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

{1320}13. _Pterocorys pipetta_, n. sp.

Shell thin-walled, smooth, with two slight strictures. Length of the three joints = 1 : 6 : 3, breadth = 1 : 3 : 1. Cephalis ovate, with a conical horn of twice the length. Thorax ovate, in the middle zone with three conical wings of the same length, curved slightly downwards (like those of _Pterocorys columba_, Pl. 71, fig. 2). Abdomen constricted into a cylindrical tube half as long as the thorax, with narrow mouth. Pores subregular, circular.

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

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

Subgenus 3. _Pterocorythium_, Haeckel.

_Definition._--Horn of the cephalis double or multiple. Abdomen not prolonged into a narrow tube.

14. _Pterocorys rhinoceros_, n. sp. (Pl. 71, fig. 1).

Shell very delicate and thin-walled, with two sharp strictures. Length of the three joints = 2 : 10 : 3, breadth, 3 : 11 : 9. Cephalis obtuse, conical, with two divergent, conical horns of equal length. Thorax triangular, pyramidal; from its three edges there arise on the middle joint three conical descending wings (little larger than the horns), and from the base of each wing descend two divergent crests, forming at the sides of the pyramid three rounded lobes. Abdomen short, cylindrical, with wide, truncate mouth. Network of the whole shell very delicate, with very small and numerous, regular, circular, hexagonally-framed pores.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.1, _c_ 0.03; breadth, _a_ 0.03, _b_ 0.11, _c_ 0.09.

_Habitat._--Central Pacific, Stations 270 to 274, surface, and in various depths.

15. _Pterocorys prismatica_, n. sp.

Shell very delicate and thin-walled throughout, with fine fenestration similar to that of the preceding species, but differing from it in the form of the abdomen, which is much larger, three-sided and prismatic; three edges of the prism decurrent from the bases of the three short wings. Length of the three joints = 1 : 4 : 5, breadth = 2 : 6 : 6. No lobes at the thorax. Mouth wide open, truncate, triangular.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.1; breadth, _a_ 0.04, _b_ 0.12, _c_ 0.12.

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

16. _Pterocorys tricornis_, n. sp.

Shell spiny, with two deep strictures. Length of the three joints = 1 : 5 : 3, breadth = 1 : 7 : 5. Cephalis subspherical, with three stout, pyramidal, divergent horns, which are three times as long, {1321}and bear three serrated edges. Thorax three-sided pyramidal, spiny; its three edges prolonged at the girdle into three stout, triangular, prismatic wings of the same length, little curved. Abdomen short, cylindrical, with wide open, truncate mouth. Pores irregular, polygonal, roundish.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.1, _c_ 0.06; breadth, _a_ 0.03, _b_ 0.14, _c_ 0.1.

_Habitat._--North Pacific, Station 244, surface.

17. _Pterocorys zittelii_, Haeckel.

_Pterocyrtidium zittelii_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol.
xxxvi. pp. 531, 540, Taf. xxxiii. figs. 28, _a_, _b_.

Shell thin-walled, rough, with two slight strictures. Length of the three joints = 2 : 5 : 7, breadth = 3 : 5 : 5. Cephalis hemispherical, armed with a very large, prismatic, vertical horn, which is half as long as the shell, and at its base surrounded by several (three to five) shorter, upwardly diverging horns. Thorax campanulate, in the upper half with three short, downwardly diverging, conical wings. Abdomen subcylindrical, with wide, truncate mouth. Pores small, subregular, circular.

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

_Habitat._--Fossil in Barbados.

18. _Pterocorys macroptera_, n. sp.

Shell thin-walled, smooth, with two slight strictures. Length of the three joints = 1 : 3 : 2, breadth = 1 : 4 : 3. Cephalis hemispherical, armed with two larger and six to eight smaller, conical, divergent horns of different lengths. Thorax three-sided pyramidal; its three edges prolonged into three very large diverging wings, which are slender, three-sided, prismatic, and nearly twice as long as the shell. Abdomen short, cylindrical, with wide, truncate mouth. Pores irregular, roundish, in the middle part of the shell (on both sides of the girdle) much larger than in the upper and lower part.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.09, _c_ 0.06; breadth, _a_ 0.04, _b_ 0.12. _c_ 0.1.

_Habitat._--South Atlantic, Station 335, surface.

Genus 583. _Theopilium_,[200] Haeckel, 1881, Prodromus, p. 435.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three lateral ribs enclosed in the wall of the thorax, without free lateral or terminal appendages.

The genus _Theopilium_ differs from all the other Theopilida in the absence of free external appendages; it has neither lateral wings nor terminal feet, but three divergent ribs are enclosed in the wall of the thorax. It agrees in this character with the Dicyrtid _Lamprodiscus_, and may be derived directly from this by development of an abdomen.

{1322}1. _Theopilium tricostatum_, n. sp. (Pl. 70, fig. 6).

Shell flatly conical, smooth. Length of the three joints = 1 : 4 : 2, breadth = 2 : 6 : 10. Cephalis subspherical, with a thin oblique horn of the same length. Thorax with three stout ribs in its wall, and with subregular, hexagonal pores increasing in size towards the girdle. Abdomen flatter than the thorax, without ribs, nearly horizontal, with subregular, square pores, disposed in four to six concentric, subcircular series of different sizes; decreasing in size towards the wide open mouth. Seen from the side, this species resembles _Corocalyptra agnesæ_, (Pl. 59, fig. 3).

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.04; breadth, _a_ 0.03, _b_ 0.12, _c_ 0.2.

_Habitat._--Central Pacific, Stations 260 to 274, surface.

2. _Theopilium triradiatum_, n. sp.

Shell flatly conical, smooth, in general of the same form as, and with similar fenestration to, the preceding species, but different in the proportions. Length of the three joints = 1 : 4 : 2, breadth = 2 : 4 : 6. Cephalis hemispherical, with two divergent, thin horns of the same length. Thorax more elevated, about as high as broad. The three divergent ribs are not limited to the thorax, but prolonged through the whole abdomen, the outline of which is a prolongation of that of the thorax.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.1, _c_ 0.05; breadth, _a_ 0.05, _b_ 0.1, _c_ 0.15.

_Habitat._--Tropical Atlantic, Station 347, surface.

3. _Theopilium cranoides_, Haeckel.

_Eucyrtidium cranoides_, Haeckel, 1862, Monogr. d. Radiol., p. 320, Taf.
vii. figs. 1-3.

Shell campanulate-conical, smooth. Length of the three joints = 2 : 5 : 4, breadth = 3 : 9 : 10. Cephalis ovate, with a straight, excentric, prismatic horn of the same length. The campanulate thorax is separated from it by no external collar stricture, but by an internal septum. From the base of the horn arise three divergent radial ribs, running in the wall of the two first joints to the lumbar stricture (_loc. cit._, Taf. vii. fig. 3). Abdomen short and wide, without ribs. Pores rather large, regular, circular, quincuncial, in the cephalis smaller. Central capsule four-lobed.

_Dimensions._--Length of the three joints, _a_ 0.027, _b_ 0.054, _c_ 0.047; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.1.

_Habitat._--Mediterranean (Messina), surface.

Genus 584. _Corocalyptra_,[201] n. gen.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three simple, free, lateral wings, arising from the collar stricture between cephalis and thorax.

The genus _Corocalyptra_ comprises a small number of very elegant hat-shaped Tricyrtida, which resemble greatly _Eucecryphalus_ among the Dicyrtida. As in the {1323}latter, three free, radial spines, or simple wings, corresponding to the three basal feet of _Cortina_, arise from the collar stricture between the small hemispherical cephalis and the large, flatly conical thorax. _Corocalyptra_ differs from _Eucecryphalus_, its ancestral form, in the development of a flat and broad abdomen, which is a prolongation of the thorax, and may be compared to the brim of a hat.

1. _Corocalyptra agnesæ_, n. sp. (Pl. 59, fig. 3).

Shell flatly conical or hat-shaped. Length of the three joints = 1 : 4 : 2, breadth = 2 : 8 : 12. Cephalis hemispherical, with an oblique, small, conical horn of the same length. From the slight collar stricture arise three slender, conical feet of equal length, twice as long as the apical horn, nearly horizontally divergent. Lateral outline of the conical thorax straight, of the flatter abdomen convex; the smooth margin of the abdomen turned inwards. Network delicate, with subregular, hexagonal pores.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.04; breadth, _a_ 0.03, _b_ 0.15, _c_ 0.24.

_Habitat._--Central Pacific, Station 270, surface.

2. _Corocalyptra elisabethæ_, n. sp. (Pl. 59, fig. 10).

Shell flatly conical, hat-shaped, very similar to the preceding species, but with different proportions. Length of the three joints = 1 : 4 : 2; breadth = 1 : 7 : 10. Cephalis very small, with an oblique horn of the same length. The three feet are of different sizes, the caudal odd foot being twice as long as the two lateral, which are equal to the horn. Lateral outline of the campanulate thorax convex, of the flatter abdomen less convex. Margin of the mouth flat.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.06, _c_ 0.03; breadth _a_ 0.02, _b_ 0.14, _c_ 0.2.

_Habitat._--Tropical Atlantic, Station 347, surface.

3. _Corocalyptra emmæ_, n. sp. (Pl. 59, fig. 4).

Shell nearly conical, hat-shaped. Length of the three joints = 1 : 3 : 1, breadth = 1 : 5 : 7. Cephalis hemispherical, with a straight horn of the same length. Feet of the collar larger than in the preceding species, the two lateral smaller being directed upwards, the larger odd caudal downwards. Thorax slightly campanulate; its hexagonal meshes two to four times as large as those of the short, convex abdomen, which is turned inwards.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.09, _c_ 0.03; breadth, _a_ 0.025, _b_ 0.13, _c_ 0.17.

_Habitat._--Central Pacific, Station 273, surface.

4. _Corocalyptra margarethæ_, n. sp.

Shell nearly conical, hat-shaped, very similar to the preceding species, but with much more delicate hexagonal network, with thread-like bars. Length of the three joints = 1 : 7 : 2, breadth = {1324}1 : 10 : 12. Cephalis hemispherical, with six bristle-shaped spines of half the length of the shell; three horns divergent upwards, and three alternating feet divergent downwards. Thorax nearly conical. Abdomen flatter.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.1, _c_ 0.03; breadth, _a_ 0.02, _b_ 0.15, _c_ 0.18.

_Habitat._--North Pacific, Station 236, surface.

5. _Corocalyptra ludovicæ_, n. sp.

Shell flatly campanulate or hat-shaped. Length of the three joints = 1 : 4 : 3, breadth = 2 : 7 : 10. Cephalis hemispherical, with six bristle-shaped spines, about one-fourth to one-third as long as the shell; three horns diverging upwards, and three alternate feet diverging downwards. Thorax nearly conical. Abdomen much larger than in all preceding species, inflated, with convex, lateral outline; its mouth-edge curved inwards. The network is much finer than in the similar _Corocalyptra emmæ_ (Pl. 59, fig. 4), and the abdomen is relatively twice as long and broad.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.06; breadth, _a_ 0.04, _b_ 0.14, _c_ 0.2.

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

Genus 585. _Dictyoceras_,[202] Haeckel, 1862, Monogr. d. Radiol., p. 333.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three latticed free lateral wings on the sides of the thorax, which are not prolonged into the cephalis.

The genus _Dictyoceras_ and the following _Pteropilium_ agree with the two preceding genera in the possession of three lateral wings on the sides of the thorax; but whilst these in the latter are simple solid spines, they are in the former vertical fenestrated plates. _Dictyoceras_ may be derived from _Pterocorys_ by development of a vertical lattice-plate between the thorax and the three free lateral spines arising from it.

1. _Dictyoceras insectum_, n. sp. (Pl. 71, figs. 6, 7).

Shell with two distinct strictures. Length of the three joints = 1 : 3 : 2, breadth = 2 : 4 : 3. Cephalis hemispherical, with a slender pyramidal horn of twice the length. Thorax subspherical, in the upper half with three divergent lattice-wings of the same length, each of which represents a slender, fenestrated, three-sided pyramid. Abdomen subovate, with wide, truncate mouth (in the figured specimen broken off). Pores circular, small, of different sizes.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.055, _c_ 0.04; breadth, _a_ 0.035, _b_ 0.08, _c_ 0.06.

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

{1325}2. _Dictyoceras formica_, n. sp. (Pl. 71, fig. 8).

Shell with obliterate collar, but deep lumbar stricture. Length of the three joints = 1 : 2 : 3, breadth = 2 : 5 : 4. Cephalis conical, with an oblique curved horn of the same length. Thorax with three vaulted swellings between the three prominent, diverging lattice-wings, the apex of which is prolonged downwards into a solid curved spine, half as long as the inflated abdomen. Mouth little constricted. Pores irregular, roundish, of different sizes.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.06; breadth, _a_ 0.03, _b_ 0.1, _c_ 0.09.

_Habitat._--North Atlantic, Station 353, surface.

3. _Dictyoceras melitta_, n. sp. (Pl. 71, fig. 9).

Shell with two deep strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 6 : 5. Cephalis subspherical, with two conical divergent horns of the same length. Thorax three-sided pyramidal, the three edges prolonged into three lattice-wings of the same form, with short, terminal spines. Abdomen inflated, subovate, with constricted mouth. Pores small, regular, circular, of equal size, with very thin bars.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.09, _c_ 0.12; breadth, _a_ 0.04, _b_ 0.18, _c_ 0.15.

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

4. _Dictyoceras bombus_, n. sp. (Pl. 71, fig. 10).

Shell with deep collar, but evanescent lumbar stricture. Length of the three joints = 1 : 5 : 3, breadth = 1 : 6 : 7. Cephalis subspherical, with a conical horn of the same length. Thorax campanulate, with three short and broad, triangular lattice-wings, the upper edge of which is nearly horizontal, the lower nearly vertical and decurrent from the height of the collar to the lumbar stricture. Abdomen inflated, with constricted mouth of half the breadth. Pores small, subregular, circular, of nearly equal size.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.1, _c_ 0.06; breadth, _a_ 0.025, _b_ 0.12, _c_ 0.14.

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

5. _Dictyoceras virchowii_, Haeckel.

_Dictyoceras virchowii_, Haeckel, 1862, Monogr. d. Radiol., p. 333, Taf.
viii. figs. 1-5.

_Lithornithium dictyoceras_, Haeckel, 1860, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, 1860, p. 840.

Shell with two distinct strictures. Length of the three joints = 1 : 3 : 4, breadth = 1 : 5 : 6. Cephalis subspherical, with an oblique curved horn of the same length. Thorax conical, with three broad, triangular lattice-wings different in size and direction, two of which are directed outwards, the third downwards--each terminated by a strong spine. Abdomen oblique, inflated, with wide open, truncate mouth. On the shell surface some few conical spines are scattered. Pores irregular, {1326}roundish, of different sizes. On the peculiar symmetry of this remarkable form, compare the detailed description in my Monograph.

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

_Habitat._--Mediterranean, Messina, surface.

Genus 586. _Pteropilium_,[203] Haeckel, 1881, Prodromus, p. 435.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three latticed free lateral wings on the sides of the thorax, prolonged into the horn of the cephalis in the form of three vertical, free cephalic wings.

The genus _Pteropilium_ differs from the preceding closely allied _Dictyoceras_ in the development of three free, vertical, latticed cephalic wings, expanded between the apical horn of the cephalis and the three wings of the thorax; they may be direct prolongations of the latter. _Pteropilium_, however, may also be derived directly from the Dicyrtida _Callimitra_ or _Clathrocorys_ by development of an abdomen. All these interesting forms are closely allied to the #Plectoidea#.

Subgenus 1. _Clathropilium_, Haeckel, 1881, Prodromus, p. 435.

_Definition._--Thorax completely latticed, without three larger lateral holes between the three wings.

1. _Pteropilium stratiotes_, n. sp. (Pl. 70, figs. 9, 10).

Shell thin-walled, with two deep strictures. Length of the three joints = 1 : 5 : 4, breadth = 2 : 6 : 9. Cephalis hemispherical, with a vertical, straight, prismatic horn of three times the length. Thorax inflated, oblique, with three slender, nearly straight, widely divergent ribs, beginning from the collar stricture and united in its centre with the centripetal prolongation of the horn. The basal half of the three ribs is enclosed in the thorax wall, whilst the distal half lies outside it, and is connected with its lower half only by two divergent, reticulated wings. The upper edge of the ribs is connected with the occipital horn by a vertical, loosely reticulated, triangular wing. Abdomen half as long as the thorax, also of irregular and oblique form, with knee-shaped outline and a wide, truncate mouth. Network with irregular polygonal, for the most part quadrangular, meshes, separated by thin bars and forming irregular transverse rows. Some stronger, vein-like ribs ramify in the wall, diverging towards the mouth.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.1, _c_ 0.08; breadth, _a_ 0.04, _b_ 0.12, _c_ 0.18.

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

{1327}2. _Pteropilium hoplites_, n. sp.

Shell in the general form and in the irregular, quadrangular fenestration similar to the preceding species, but more heavy and with different proportions. Length of the three joints = 1 : 6 : 4, breadth = 2 : 6 : 8. Cephalis twice as broad as in _Pteropilium stratiotes_. Thorax more slender and subovate. Abdomen truncate, conical, gradually dilated, with straight, non-geniculate outline. Network coarser, with larger square meshes and thicker bars.

_Dimensions._--Length of the three joints, _a_ 0.03, _b_ 0.12, _c_ 0.08; breadth, _a_ 0.05, _b_ 0.12, _c_ 0.16.

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

3. _Pteropilium eques_, n. sp.

Shell in the general form and in the irregular, quadrangular fenestration similar to those of the two preceding species, but more slender and with different proportions. Length of the three joints = 1 : 3 : 2, breadth = 2 : 4 : 4. Cephalis flatter. Thorax subconical, also flatter. Abdomen short, cylindrical, with straight outline. Network looser than in the two preceding species, with larger square meshes and thinner bars.

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

_Habitat._--Central Pacific, Station 274, depth 2750 fathoms.

Subgenus 2. _Arachnopilium_, Haeckel, 1881, Prodromus, p. 435.

_Definition._--Thorax with three large lateral holes between the three latticed wings.

4. _Pteropilium clathrocanium_, n. sp. (Pl. 64, fig. 7).

_Arachnopilium clathrocanium_, Haeckel, Prodromus, 1881, p. 435.

Shell very delicate, with two deep strictures. Length of the three joints = 2 : 4 : 2, breadth = 2 : 10 : 5. Cephalis subspherical, with circular, polygonally-framed pores, and a central, three-sided pyramidal, apical horn of twice the length. Thorax three-sided pyramidal, with three large, ovate holes between three prominent latticed wings. From its surface arises a very delicate, arachnoidal network with irregular, polygonal meshes, enveloping also the entire cephalis. Abdomen wide and short, as long as the cephalis, and half as broad as the distance of the wings, twice as broad as the constricted mouth.

_Dimensions._--Length of the three joints, _a_ 0.04, _b_ 0.08, _c_ 0.04; breadth, _a_ 0.05, _b_ 0.2, _c_ 0.1.

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

{1328}Genus 587. _Theopodium_,[204] Haeckel, 1881, Prodromus, p. 435.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three divergent solid ribs, which lie in the wall of the thorax and the abdomen, and are prolonged into three solid terminal feet.

The genus _Theopodium_ and the following closely allied _Pterocanium_ differ from the preceding four genera in the development of the three radial rods or the primary cortinar spines, which are not free lateral wings, but longitudinal ribs enclosed in the wall of the thorax and abdomen, and prolonged over the basal mouth into three free terminal feet. These are solid in _Theopodium_, which, therefore, corresponds to _Lychnocanium_ among the Dicyrtida.

1. _Theopodium tricostatum_, n. sp. (Pl. 97, fig. 14).

Shell three-sided pyramidal, thorny, with two distinct strictures. Length of the three joints = 1 : 2 : 2, breadth = 1 : 3 : 4. Cephalis hemispherical, with a stout conical horn of the same length. Thorax with regular, circular, hexagonally-framed pores. Abdomen with irregular, roundish pores of very different sizes. From the middle part of the thorax arise the three prominent, wing-like edges of the pyramid, which are prolonged over its wide mouth into three stout, pyramidal, divergent feet about as long as the thorax, with dentate, lamellar edges.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.07, _c_ 0.06; breadth, _a_ 0.04, _b_ 0.09, _c_ 0.12.

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

2. _Theopodium pyramidale_, n. sp.

Shell three-sided pyramidal, rough, without external strictures, but with two broad internal girdles. Length of the three joints = 1 : 2 : 6, breadth = 2 : 4 : 8. Cephalis with a thick horn of the same length, conical. Thorax with very small, regular, circular pores. Abdomen with irregular, roundish pores of very different sizes. From the collar stricture arise the three rectilinear edges of the pyramid, which are prolonged over its wide-open mouth into three stout, divergent, pyramidal feet, about as long as the thorax.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.12; breadth, _a_ 0.04, _b_ 0.075, _c_ 0.15.

_Habitat._--Fossil in Barbados.

Genus 588. _Pterocanium_,[205] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three divergent ribs, which run along the thorax and abdomen, and are prolonged into three latticed terminal feet.

{1329}The genus _Pterocanium_ differs from the preceding _Theopodium_ in the fenestration of the three terminal feet, which are basal prolongations of the three radial ribs, enclosed in the wall of the thorax and the abdomen. Often also these ribs are partly or wholly fenestrated. It corresponds to _Lychnodictyum_ among the Dicyrtida, and may be derived from this by development of an abdomen. The latter forms sometimes three concave bays, at other times three convex lobes between the three latticed feet.

Subgenus 1. _Pterocanarium_, Haeckel.

_Definition._--Free basal edge of the abdomen between the three feet concave, forming three shallower or deeper bays between them.

1. _Pterocanium proserpinæ_, Ehrenberg.

_Pterocanium proserpinæ_, Ehrenberg, 1858, Abhandl. d. k. Akad. d. Wiss.
Berlin, 1872, p. 299, Taf. xi. fig. 22.

_Pterocanium proserpinæ_, Haeckel, 1862, Monogr. d. Radiol., p. 332.

Shell campanulate, rough. Length of the three joints = 1 : 4 : 2, breadth 1 : 5 : 6. Cephalis subspherical, with a triangular-pyramidal vertical horn of thrice the length. Thorax hemispherical, without prominent swellings. Abdomen shorter, with three concave basal bays. Pores in the thorax and abdomen nearly equal, subregular, circular. Feet from the girdle (or the lumbar stricture) little divergent, nearly straight.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.04; breadth, _a_ 0.3, _b_ 0.1, _c_ 0.12.

_Habitat._--Mediterranean, Candia, Spratt, depth 1100 fathoms.

2. _Pterocanium gravidum_, n. sp., (Pl. 73, fig. 3).

Shell campanulate, nearly three-sided pyramidal, smooth. Length of the three joints = 1 : 4 : 3, breadth = 1 : 6 : 10. Cephalis subspherical, with a pyramidal straight horn of twice the length. Thorax hemispherical, without prominent swellings. Abdomen shorter, with three concave basal bays; its network prolonged to the ends of the feet. Pores in the thorax and abdomen of nearly equal size, irregular, roundish. Feet from the girdle strongly divergent, with convex back.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.075, _c_ 0.06; breadth, _a_ 0.02, _b_ 0.12, _c_ 0.2.

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

3. _Pterocanium orcinum_, n. sp. (Pl. 73, fig. 2).

Shell campanulate, nearly three-sided pyramidal, covered with conical spines. Length of the three joints = 1 : 4 : 3, breadth = 1 : 5 : 6. Cephalis hemispherical, with a conical horn of the same length. Thorax without prominent swellings, with subregular, circular pores. Abdomen {1330}shorter, with three concave basal edges and irregular, polygonal pores. Feet from the girdle strongly divergent, nearly straight.

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

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

4. _Pterocanium contiguum_, Ehrenberg.

_Pterocanium contiguum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, Taf. xvii. fig. 7.

Shell three-sided pyramidal, smooth. Length of the three joints = 1 : 3 : 2, breadth = 1 : 4 : 6. Cephalis small, subspherical, with a large conical horn three times the length. Thorax and abdomen with small, regular, circular pores of equal size, densely crowded together, with thin bars. Abdomen shorter, with three concave basal edges. Feet very thick, straight, from the girdle strongly divergent.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.05, _c_ 0.025; breadth _a_ 0.02, _b_ 0.08, _c_ 0.12.

_Habitat._--Fossil in Barbados.

5. _Pterocanium pyramis_, n. sp. (Pl. 68, fig. 7).

Shell three-sided pyramidal, smooth. Length of the three joints = 1 : 4 : 3, breadth = 2 : 4 : 6. Cephalis hemispherical, with a conical horn of the same length. Thorax campanulate, with fifteen to twenty prominent longitudinal ribs, separating as many rows of regular, circular pores. Abdomen shorter, with three concave basal bays, and irregular, roundish pores. Feet very strong, pyramidal, straight, gradually divergent from the girdle.

_Dimensions._--Length of the three joints, _a_ 0.025, _b_ 0.08, _c_ 0.06; breadth, _a_ 0.04, _b_ 0.08, _c_ 0.12.

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

6. _Pterocanium virgineum_, n. sp. (Pl. 73, fig. 6).

Shell nearly three-sided pyramidal, smooth. Length of the three joints = 1 : 4 : 8, breadth 2 : 6 : 9. Cephalis hemispherical, with a conical straight horn three times the length. Thorax campanulate, with three slight swellings between the three knee-shaped ribs, and with regular circular pores. Abdomen longer, with three concave basal bays, and with very small and numerous pores (much smaller than those of the thorax). At both sides of the three prominent abdominal crests, two rows of larger, nearly square pores occur. Feet slender, nearly straight, divergent.

_Dimensions._--Length of the three joints, _a_ 0.15, _b_ 0.06, _c_ 0.12; breadth, _a_ 0.03, _b_ 0.09, _c_ 0.14.

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

7. _Pterocanium prætextum_, Haeckel.

Lychnocanium prætextum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 297, Taf. x. fig. 2.

Shell nearly three-sided prismatic, smooth. Length of the three joints = 1 : 2 : 1, breadth = 1 : 4 : 4. Cephalis subspherical, with a straight, conical horn of three times the length. Thorax {1331}campanulate with three slight swellings between the three knee-shaped ribs, and with regular, circular pores. Abdomen smaller, with three deep concave basal bays, and with irregular, roundish pores. Feet longer than the shell, slender, pyramidal, straight, parallel.

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

_Habitat._--Indian Ocean, Ceylon (Haeckel); Zanzibar (Pullen).

8. _Pterocanium depressum_, Haeckel.

_Lychnocanium depressum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 297, Taf. x. fig. 1.

Shell (including the feet) nearly three-sided prismatic, rough. Length of the three joints = 1 : 2 : 1, breadth = 1 : 6 : 6. Cephalis subspherical, with a conical horn of the same length. Thorax a very flat and broad triangular pyramid, three times as broad as long. Abdomen smaller, with three deep, parabolic, concave bays. Pores irregular, roundish. Feet longer than the shell, slender, pyramidal, straight, parallel.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.04, _c_ 0.02; breadth, _a_ 0.025, _b_ 0.12, _c_ 0.12.

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

9. _Pterocanium campanella_, Haeckel.

_Lychnocanium campanella_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 297, Taf. viii. fig. 12

_Podocyrtis campanella_, Ehrenberg, Monatsber. d. k. preuss. Akad. d.
Wiss. Berlin, p. 769.

Shell campanulate, smooth, with three high fenestrated crests and deep collar stricture. Length of the three joints = 1 : 3;1, breadth = 1 : 4 : 3. Cephalis subspherical, with a slender horn of the same length. Thorax inflated, campanulate, with three vaulted swellings between the three curved ribs. Abdomen short, with three semicircular bays between the three feet. Pores of the whole shell regular, circular, small, and numerous. Feet broad, triangular, shorter than the thorax, with convex back and convergent ends.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.06, _c_ 0.2; breadth _a_ 0.02, _b_ 0.08, _c_ 0.07.

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

10. _Pterocanium tricolpum_, n. sp. (Pl. 73, fig. 1).

Shell nearly three-sided prismatic, smooth, with three high fenestrated crests and two deep strictures. Length of the three joints = 1 : 3 : 2, breadth = 1 : 5 : 5. Cephalis subspherical, with an oblique, conical horn of the same length. Thorax inflated, with three highly vaulted bosoms between the three high crests, and with subregular, circular pores. Abdomen shorter, with three concave (or nearly rectangular, square) basal bays between the three feet, and with irregular, roundish pores, three to four pairs of larger pores occurring at the sides of the base of the feet. Feet nearly as long as the shell, with fenestrated bases, nearly straight and parallel; somewhat convergent, with convex back. (Often the concave bays between the three feet are not square, as in the specimen figured, but {1332}semicircular.) The ends of the feet are sometimes strongly convergent. The vaultings of the three swellings and the reticulation are also variable; the whole form is often irregular.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.04; breadth, _a_ 0.025, _b_ 0.1, _c_ 0.1.

_Habitat._--Cosmopolitan; Atlantic, Pacific; many stations, surface.

Subgenus 2. _Pterocanidium_, Haeckel.

_Definition._--Free basal edge of the abdomen between the three feet convex, forming three rounded or semicircular prominent lobes between them.

11. _Pterocanium eucolpum_, n. sp. (Pl. 73, fig. 4).

_Dictyopodium eucolpum_, Haeckel, 1881, Prodromus et Atlas.

Shell about triangular-prismatic, with two deep strictures, smooth. Length of the three joints = 1 : 3 : 3, breadth = 1 : 3 : 4. Cephalis subspherical, with a conical, oblique horn of the same length. Thorax inflated, with three hemispherical swellings between the three crests, and with subregular, hexagonal pores. Abdomen longer, with much smaller, irregular, roundish pores, forming three broad, convex lobes between the three feet. (In the figured specimen the lobes were not fully developed, and extremely thin below the line parallel to the edge. In another specimen, found afterwards in the same locality, the three lobes were much larger, semicircular, and reached almost to the basal plane of the ends of the feet by reason of their convexity.) Feet strong, with slightly convex back, divergent.

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

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

12. _Pterocanium bicorne_, n. sp. (Pl. 73, fig. 5).

_Dictyopodium bicorne_, Haeckel, 1881, Prodromus et Atlas.

Shell nearly three-sided pyramidal, slender, smooth. Length of the three joints = 1 : 2 : 2, breadth = 1 : 4 : 4. Cephalis hemispherical, with two oblique, conical horns of nearly equal length. Thorax nearly hemispherical, with slightly prominent crests, and with subregular, hexagonal pores. Abdomen of about the same length, with much smaller, irregular, roundish pores, forming three convex, nearly circular lobes between the three large divergent feet. These are slender, three-sided pyramidal, longer than the shell, fenestrated at the thickened base, with some rows of larger pores; their back is slightly concave.

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

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

{1333}13. _Pterocanium trilobum_, Haeckel.

_Dictyopodium trilobum_, Haeckel, 1882, Monogr. d. Radiol., p. 340, Taf.
viii. figs. 6-10.

Shell three-sided pyramidal, nearly tetrahedral, covered with conical spines. Length of the three joints = 1 : 4 : 2, breadth = 1 : 6 : 10. Cephalis hemispherical, with a large conical horn (as long as the thorax). Thorax tetrahedral, with little prominent crests. Abdomen forming three semicircular, convex lobes between the three feet, half as long as the thorax, with the same irregular, roundish pores. Feet slender, about as long as the shell, triangular, with convex back, strongly divergent, fenestrated at the inflated and thickened base. (Compare the special description of the living form and its soft body in my Monograph.)

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.08, _c_ 0.04; breadth, _a_ 0.03, _b_ 0.12, _c_ 0.2.

_Habitat._--Mediterranean, Messina, surface.

Genus 589 _Pterocodon_,[206] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three solid free lateral wings on the thorax, and numerous solid terminal feet around the mouth of the abdomen.

The genus _Pterocodon_ differs from the closely allied _Pterocorys_, its ancestral form, in the development of numerous solid feet around the terminal mouth, similar to the terminal corona of _Calocyclas_.

1. _Pterocodon campana_, Ehrenberg.

_Pterocodon campana_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 10.

_Pterocodon campana_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 82, Taf. xix. fig. 1.

Shell slender, campanulate, subconical, with two distinct strictures. Length of the three joints = 1 : 2 : 4, breadth = 2 : 3 : 5. Cephalis hemispherical, with a conical horn of twice the length. Thorax hemispherical, in the upper part with three divergent, conical horns, as long as the cephalis, and curved downwards. Abdomen with four transverse rows of large circular pores, increasing in size towards the mouth; the largest (undermost), five times as broad as the circular thoracic pores. Mouth not constricted, with a corona of twelve to fifteen divergent, conical feet.

_Dimensions._--Length of the three joints, _a_ 0.015, _b_ 0.03, _c_ 0.06; breadth, _a_ 0.02, _b_ 0.05, _c_ 0.08.

_Habitat._--Fossil in Barbados.

2. _Pterocodon ornatus_, n. sp. (Pl. 70, fig. 11).

Shell nearly ovate, with two deep strictures. Length of the three joints = 1 : 3 : 5, breadth = 1 : 5 : 7. Cephalis hemispherical, with a large oblique horn reaching half the length of the {1334}shell; three edges of the horn wing-shaped and dentated. Thorax hemispherical, in the middle zone with three conical wings, which are half as long as the thorax, and curved downwards. Pores hexagonal, roundish, twice as broad in the inflated abdomen as in the thorax. Mouth constricted, with a corona of from fifteen to eighteen conical, divergent, curved feet, similar to the thoracic wings.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.1; breadth, _a_ 0.025, _b_ 0.1, _c_ 0.14.

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

3. _Pterocodon favosus_, n. sp.

Shell ovate, with two slight strictures. Length of the three joints = 1 : 2 : 2, breadth = 2 : 4 : 4. Cephalis hemispherical, with a conical horn of twice the length. Three wings of the thorax equal to those of the preceding species. Pores regular, circular, hexagonally framed, of equal size in the thorax and abdomen. Mouth constricted, with a corona of nine straight, conical, nearly vertical feet.

_Dimensions._--Length of the three joints, _a_ 0.0025, _b_ 0.05, _c_ 0.05; breadth, _a_ 0.05, _b_ 0.09, _c_ 0.1.

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

Genus 590. _Dictyocodon_,[207] Haeckel, 1881, Prodromus, p. 435.

_Definition._--#Theopilida# (vel Tricyrtida triradiata aperta) with three latticed free lateral wings on the thorax, and numerous latticed terminal feet around the mouth of the abdomen.

The genus _Dictyocodon_, one of the most elegant among the NASSELLARIA, differs from the preceding _Pterocodon_ in the fenestration of the three lateral wings of the thorax, and the numerous terminal feet of the abdomen. It may be derived from _Dictyoceras_ by development of regular lattice-feet around the terminal mouth.

Subgenus 1. _Dictyocodella_, Haeckel.

_Definition._--The three lateral lattice-wings arise from the thorax alone.

1. _Dictyocodon annasethe_, n. sp. (Pl. 71, fig. 11).

Shell with two deep strictures. Length of the three joints = 2 : 5 : 4, breadth = 1 : 5 : 6. Cephalis subspherical, with a very large, three-sided prismatic horn of three times the length, bearing at the base some smaller accessory spines. Thorax nearly conical, with three large, inflated, triangular lattice-wings, the upper edge of which (the cortinar rod) descends obliquely, and is larger {1335}than the thorax, ending in a spine. Abdomen inflated, subcylindrical, divided at the wide open mouth by nine deep incisions into nine large triangular feet. Network in the thorax and wings composed of small, regular, hexagonal pores, in the abdomen of three transverse rows of irregular, very large pores, which are surrounded and separated by bands of very small pores; in each foot one large pore and a marginal series of very small pores occur. I dedicate this wonderful species to the memory of my dear wife, Anna Sethe.

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

_Habitat._--Indian Ocean; Cocos Islands (Rabbe), surface.

2. _Dictyocodon carolotæ,_ n. sp. (Pl. 71, fig. 14).

Shell with two deep strictures. Length of the three joints = 1 : 3 : 7, breadth = 2 : 5 : 6. Cephalis hemispherical, with an oblique pyramidal horn of twice the length. Thorax subconical, in the upper half with three divergent, triangular wings of half the length, the upper edge of which is nearly horizontal, little curved. Abdomen nearly cylindrical; divided at the wide open mouth by nine deep incisions into nine triangular, vertical feet, about as large as the wings. Network very delicate, with regular, small, circular pores of equal size and very thin bars. I dedicate this elegant species to my dear mother, Charlotte Sethe.

_Dimensions._--Length of the three joints, _a_ 0.02, _b_ 0.06, _c_ 0.14; breadth, _a_ 0.04, _b_ 0.1, _c_ 0.12.

_Habitat._--Cape of Good Hope (Bleek), surface.

Subgenus 2. _Dictyocodoma_, Haeckel.

_Definition._--The three lateral wings are prolonged from the thorax to the abdomen.

3. _Dictyocodon palladius_, n. sp. (Pl. 71, figs. 12, 13).

Shell with distinct collar, but evanescent lumbar stricture. Length of the three joints = 1 : 2 : 7, breadth = 1 : 3 : 8. Cephalis very small, with a large pyramidal horn of twice the length, bearing at its base some small, often branched, accessory spines. Thorax three-sided pyramidal, without external boundary prolonged into the large, inflated, gradually dilated abdomen. The internal boundary between the two is marked by a fenestrated, horizontal ring (not indicated in the figure). Three prominent, triangular, fenestrated wings arise from the base of the cephalic horn, and are prolonged nearly through the whole shell almost to the edge of the mouth; in its lower half they form three elevated fenestrated apophyses, the upper edge of which is nearly horizontal. Mouth divided by about twenty incisions into as many triangular, vertical, fenestrated feet. The network of the whole shell is very delicate, like fine gauze, composed of very small, regular, hexagonal pores.