Chapter XV: Section II: DICYRTIDA, Haeckel, 1862, Monogr. d. Radiol., pp. 280, 296 (1)

_Definition._--#Cyrtoidea# dithalamia, with two-jointed shell, being divided by a transverse collar stricture into an apical joint (or cephalis) and a basal joint (or thorax).

_Synopsis of the three Families and six Subfamilies of Dicyrtida._

Family LXII. Tripocyrtida. { Mouth open, 1. Sethopilida.
{
Three radial apophyses. { Mouth closed, 2. Sethoperida.

Family LXIII. Anthocyrtida. { Mouth open, 3. Sethophormida.
{
Numerous radial apophyses. { Mouth closed, 4. Sethophænida.

Family LXIV. Sethocyrtida. { Mouth open, 5. Sethocorida.
{
No radial apophyses. { Mouth closed, 6. Sethocapsida.

Family LXII. #TRIPOCYRTIDA#, n. fam.

_Sethopilida et Sethoperida_, Haeckel, 1881, Prodromus, pp. 431, 433.

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

{1193}The family #Tripocyrtida#, composed of the Sethopilida and Sethoperida of my Prodromus, comprises those #Cyrtoidea# in which the lattice-shell is two-jointed and bears three radial apophyses. The two subfamilies differ in the shape of the mouth, which in the Sethopilida is a simple wide opening, but in the Sethoperida is closed by a lattice-plate; the former are here divided into sixteen, the latter into eight different genera. Though probably the two shell-joints are not truly homologous in all Tripocyrtida, we call the first joint here, as in all Dicyrtida, the cephalis, and the second joint the thorax.

Numerous Tripocyrtida, living as well as fossil forms, were formerly described by Ehrenberg. His genera _Dictyophimus_, _Clathrocanium_, _Lithomelissa_, and _Lychnocanium_ belong to the Sethopilida, and have the mouth open; his genera _Lithopera_ and _Lithochytris_ (partly) belong to the Sethoperida, and have the basal mouth closed by a lattice-plate. Many of these Tripocyrtida belong probably to the oldest forms of Dicyrtida, are nearly related to the Phormospyrida, and therefore of special phylogenetic interest, as was demonstrated by Bütschli (1882, _loc. cit._, pp. 514-519). This near relation to certain #Spyroidea# (_Tripospyris_, _Acrospyris_, &c.) is particularly striking in some forms of _Clathrocanium_, _Lithomelissa_, &c. Some other Tripocyrtida seem to possess a closer relation to certain #Plectoidea# (_Plagoniscus_, _Plectaniscus_), so mainly some forms of _Tripocyrtis_ and _Dictyophimus_.

The cephalis, or the first joint of the shell, corresponds usually to the whole shell of the Zygospyrida and of numerous Monocyrtida, and exhibits various modifications of shape, which have been already described in these latter families. It is usually subspherical or hemispherical and armed with an apical horn. In a small number of genera the horn is lost, in some other genera multiplied. The cephalis is separated from the thorax not only externally by the collar constriction, but commonly also internally by a transverse horizontal fenestrated septum, which usually exhibits three or four characteristic cortinar pores. The central capsule, originally enclosed in the cephalis, develops usually three or four large pear-shaped cæcal sacs which pass through the cortinar pores and depend into the thorax (Pl. 55, figs. 2-11; Pl. 60, figs. 3-7, &c.).

The thorax in this family exhibits a great variety of interesting modifications, mainly in the development of the three radial apophyses arising from it. These may be either enclosed in the wall of the thorax as ribs, or arise as free wings, very often prolonged over the mouth as three terminal feet. Finally the three terminal feet only remain, whilst the original ribs are lost. The special ornamentation of these three apophyses exhibits an extraordinary variety and elegancy of structure, and many Tripocyrtida belong, no doubt, to the most graceful and admirable forms of NASSELLARIA.

{1194}_Synopsis of the Genera of Tripocyrtida._

-------------------------------------------------------------------------
I. Subfamily Sethopilida.
Terminal mouth of the thorax a simple wide opening.
--------------------
A. Three radial ribs (or cortinar rods) partly or completely enclosed in
the wall of the thorax. No latticed vertical cephalic wings.
-------------------------------------------------------------------------
a. Three thoracic { { Feet solid, 534. _Dictyophimus_.
ribs prolonged { Cephalis {
into three { with a horn. { Feet latticed, 535. _Tripocyrtis_.
terminal feet. {
{ No horn, feet solid, 536. _Sethopilium_.

{ Thorax { With horn, 537. _Lithomelissa_.
{ perfectly {
b. Three thoracic { latticed. { No horn, 538. _Psilomelissa_.
ribs prolonged {
into three { Thorax with spongy framework, 539. _Spongomelissa_.
lateral wings. {
{ Thorax with three large
{ lateral holes between
{ the three ribs, 540. _Clathrocanium_.

c. Three thoracic {
ribs completely { Peristome simple, smooth, 541. _Lamprodiscus_.
enclosed in the {
wall of the { Peristome with a corona of
flat thorax { spines, 542. _Lampromitra_.
-------------------------------------------------------------------------
B. Three radial ribs enclosed in the wall of the thorax and connected
with the cephalic horn by three latticed vertical wings.
-------------------------------------------------------------------------
a. Thorax { No frontal horn (four spines), 543. _Callimitra_.
completely {
latticed { With frontal horn (five
{ spines), 544. _Clathromitra_.

b. Thorax with three large lateral holes between
the three ribs. No frontal horn, 545. _Clathrocorys_.
-------------------------------------------------------------------------
C. Three radial beams (or cortinar rods) perfectly free, not enclosed in
the wall of the thorax.
-------------------------------------------------------------------------
Three beams outside the thorax, arising freely
from the collar stricture (no cephalic hole), 546. _Eucecryphalus_.

Three beams inside the thorax. Cephalis with
a large apical hole, 547. _Amphiplecta_.
-------------------------------------------------------------------------
D. Three radial terminal feet on the peristome (the three original
lateral ribs are lost).
-------------------------------------------------------------------------
Feet solid, 548. _Lychnocanium_.

Feet latticed, 549. _Lychnodictyum_.
-------------------------------------------------------------------------
II. Subfamily Sethoperida.
Terminal mouth of the thorax closed by a lattice-plate.
--------------------
Three divergent ribs (or cortinar rods) enclosed either in the wall
or in the cavity of the thorax.
-------------------------------------------------------------------------
Three ribs enclosed in the lattice-wall of the
thorax, 550. _Sethopera_.

Three internal rods in the cavity of the thorax, 551. _Lithopera_.
-------------------------------------------------------------------------
Three divergent free lateral wings (as prolongation of the three ribs)
on the sides of the thorax.
-------------------------------------------------------------------------
Three solid { Cephalis with horn, 552. _Micromelissa_.
lateral spines. {
{ No horn, 553. _Peromelissa_.

Three latticed lateral wings. With horn, 554. _Sethomelissa_.
-------------------------------------------------------------------------
Three free terminal feet (on the base of the thorax).
-------------------------------------------------------------------------
Three feet solid, 555. _Tetrahedrina_.

{ Shell without external
Three feet { mantle, 556. _Sethochytris_.
latticed. {
{ Shell with an arachnoidal
{ mantle, 557. _Clathrolychnus_.

{1195}Subfamily 1. SETHOPILIDA, Haeckel, 1881, Prodromus, p. 431.

_Definition._--#Tripocyrtida#, with the basal mouth of the shell open (vel Dicyrtida triradiata aperta).

Genus 534. _Dictyophimus_,[151] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 53.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, prolonged into three solid divergent feet on the peristome. Cephalis with an apical horn.

The genus _Dictyophimus_, comprising many common species, may be regarded as the common ancestral form of all sethopilida, and therefore also of the whole family of Dicyrtida. The cephalis bears an apical horn, and the thorax three ribs, which are prolonged over the open mouth into three solid feet. _Dictyophimus_ may be derived either from _Euscenium_ or _Peridium_ (Archiperida), or from _Tripospyris_ (Zygospyrida), or from _Plectaniscus_ (Plectanida), by development of lattice-work between the three terminal feet, which therefore become thoracic ribs.

Subgenus 1. _Dictyophimium_, Haeckel.

_Definition._--Shell smooth or rough, without prominent spines on the edges of the three thoracic ribs. (Commonly one single horn on the cephalis.)

1. _Dictyophimus sphærocephalus_, n. sp. (Pl. 57, fig. 10).

Shell smooth, with a deep collar stricture, separating two joints of nearly equal size. Cephalis subglobular, rough, with a stout pyramidal horn of half the length, and regular, circular, hexagonally framed pores. Thorax nearly three-sided prismatic, smooth, with three stout, little divergent or nearly parallel ribs, which are prolonged into conical subvertical feet half as long. Thoracic pores irregular, roundish.

_Dimensions._--Cephalis 0.08 long, 0.08 broad; thorax 0.08 long, 0.08 broad.

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

2. _Dictyophimus_ tripus, Haeckel.

_Dictyophimus tripus_, Haeckel, 1862, Monogr. d. Radiol., p. 306, Taf.
vi. fig. 1.

Shell with a slight collar stricture, separating two joints of slightly different size. Cephalis nearly ellipsoidal, large, with a slender conical horn of the same length. Thorax truncate three-sided {1196}pyramidal, with three strongly divergent ribs, which are prolonged into three slender conical feet of about the same length. Pores irregular, roundish, of variable size.

_Dimensions._--Cephalis 0.032 long, 0.028 broad; thorax 0.34 long, 0.064 broad.

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

3. _Dictyophimus plectaniscus_, n. sp. (Pl. 61, figs. 8, 9).

Shell flat, pyramidal, smooth, with distinct collar stricture. Cephalis hemispherical, with a conical horn of the same length and numerous small regular pores. Thorax flat, triangular, pyramidal, with three widely divergent ribs, which are prolonged into three cylindrical feet of the same length. Thoracic pores fifteen, very large, subregular, roundish, disposed in two transverse girdles, the inner with six, the outer with nine pores; five pores between every two ribs.

_Dimensions._--Cephalis 0.04 long, 0.06 broad; thorax 0.08 long, 0.18 broad.

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

4. _Dictyophimus craticula_, Ehrenberg.

_Dictyophimus craticula_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. v. figs. 4, 5.

_Dictyophimus craticula_, Bütschli, 1882, Zeitschr. f. Wiss. Zool., vol.
xxxvi. p. 515, Taf. xxxiii. fig. 35.

Shell flat, pyramidal, very similar to the preceding species, but differing in the rudimentary horn, which is smaller than half the cephalis, and in the length of the three cylindrical feet, which are twice to three times as long as the shell. The nine inferior large pores of the thorax are twice to three times as large as the six superior pores. The basal peristome is commonly thorny.

_Dimensions._--Cephalis 0.04 long, 0.05 broad; thorax 0.1 long, 0.2 broad.

_Habitat._--Fossil in Barbados.

5. _Dictyophimus pyramis_, n. sp. (Pl. 61, fig. 16).

Shell regular, pyramidal, with flat collar stricture. Relative length of the two joints = 1 : 4, breadth = 2 : 6. Cephalis hemispherical, with a stout pyramidal horn of the same length. Thorax triangular pyramidal, with three prominent ribs, which are prolonged into three slender pyramidal feet, half as long. Pores small and very numerous, subregular, circular.

_Dimensions._--Cephalis 0.03 long, 0.05 broad; thorax 0.1 long, 0.15 broad.

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

6. _Dictyophimus challengeri_, Haeckel.

_Dictyophimus challengeri_, Haeckel, 1878, Protistenreich, p. 47, fig.
35.

Shell campanulate, with sharp collar stricture. Relative length of the joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a stout pyramidal horn of twice the length, and numerous {1197}very small pores. Thorax nearly hemispherical, with three vaulted bosoms between the three decurrent ribs, which are prolonged into three nearly parallel and vertical feet of about the same length. Pores subregular, circular, of medium size. This species is very similar to _Lychnodictyum challengeri_, Haeckel, but differs in the smaller straight horn and the longer solid feet, which are not fenestrated.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.09 long, 0.13 broad.

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

7. _Dictyophimus lasanum_, n. sp. (Pl. 61, fig. 5).

Shell nearly pear-shaped, with distinct collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 3. Cephalis hemispherical, with a conical horn of the same length. Thorax nearly spherical, on both poles truncate and constricted, with three decurrent curved ribs and small regular circular pores. The prolongations of the ribs form three divergent pyramidal straight feet, nearly as long as the thorax.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.09 long, 0.09 broad.

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

8. _Dictyophimus longipes_, n. sp. (Pl. 61, fig. 3).

Shell three-sided pyramidal, with distinct collar stricture. Relative length of the two joints = 1 : 4, breadth = 2 : 6. Cephalis hemispherical, with a rudimentary pyramidal horn, scarcely one-fourth as long; and with small circular regular pores. Thorax with larger irregular pores, and three vaulted bosoms between the three decurrent ribs, which are prolonged into three very long and slender prismatic feet, S-shaped, curved, and twice to three times as long as the shell.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.09 long, 0.13 broad.

_Habitat._--South Pacific, Station 300, depth 1375 fathoms.

9. _Dictyophimus gracilipes_, Bailey.

_Dictyophimus gracilipes_, Bailey, 1856, Amer. Journ. Sci. and Arts, vol.
xxii. p. 4, pl. i. fig. 8.

Shell three-sided pyramidal, with a deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis hemispherical, with a thin horn of the same length. Thorax with three curved ribs, which are prolonged into three divergent angular feet of the same length. Pores irregular roundish.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.05 long, 0.08 broad.

_Habitat._--North Pacific, Station 240, surface, Kamtschatka (Bailey).

10. _Dictyophimus cortina_, n. sp. (Pl. 61, fig. 1).

Shell three-sided pyramidal, with distinct collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a pyramidal horn of half the length. Thorax {1198}with much larger irregular roundish pores and three prominent ribs, which are prolonged into three stout, club-shaped, strongly divergent feet of the same length. Mouth widely open, elegantly coronate, with a circle of numerous small cilia.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.06 long, 0.08 broad.

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

11. _Dictyophimus arabicus_, Haeckel.

_Lychnocanium arabicum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 296, Taf. x. fig. 3.

Shell smooth, three-sided pyramidal, with deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a slender horn of the same length. Thorax with much larger, irregular roundish pores, and three widely divergent ribs, which are prolonged into three slender, somewhat recurved feet of about the same length.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.07 long, 0.09 broad.

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

12. _Dictyophimus platycephalus_, n. sp. (Pl. 60, figs. 4, 5).

Shell smooth, flat, three-sided pyramidal, with distinct collar stricture. Relative length of the two joints = 1 : 3, breadth = 3 : 9. Cephalis flat, cap-shaped, three times as broad as long, with a slender conical horn of the same length. Thorax flatly vaulted, with much larger, irregular roundish, double-edged pores, and three widely divergent ribs, which are prolonged into three slender conical feet of the same length. Central capsule in the cephalis flat, discoidal, with a discoidal nucleus of half the size, and with four large pear-shaped cæcal sacs depending into the thorax, each of which contains a large oil globule (fig. 4).

_Dimensions._--Cephalis 0.02 long, 0.07 broad; thorax 0.06 long, 0.18 broad.

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

13. _Dictyophimus brandtii_, n. sp. (Pl. 60, fig. 6).

Shell smooth, flat, three-sided pyramidal, with deep collar stricture, very similar to the preceding species. Relative length of the two joints = 1 : 3, breadth = 2 : 7. Cephalis hemispherical, with a slender conical horn of twice the length. Thorax flatly vaulted, with irregular polygonal pores and thin bars; and with three widely divergent ribs, which are prolonged into three slender prismatic feet of thrice the length. In fig. 6 the shell is seen from the base and exhibits very distinctly the collar septum with its four large meshes, two minor jugular and two major cardinal pores.

_Dimensions._--Cephalis 0.03 long, 0.07 broad; thorax 0.08 long, 0.2 broad.

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

{1199}14. _Dictyophimus lucerna_, Haeckel.

_Lychnocanium lucerna_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 6;
Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 80, Taf. viii. fig. 3.

_Lychnocanium lucerna_, Haeckel, 1862, Monogr. d. Radiol., p. 311.

Shell smooth, three-sided pyramidal, with slight collar stricture. Relative length of the two joints = 1 : 4, breadth = 1 : 4. Cephalis hemispherical, with a thick conical horn of twice the length. Thorax with small regular, circular pores and three flat sides; between these arise three rounded ribs, which are prolonged into three short, conical, divergent feet, one-third as long as the thorax.

_Dimensions._--Cephalis 0.02 long, 0.025 broad; thorax 0.08 long, 0.08 broad.

_Habitat._--Fossil in Barbados.

15. _Dictyophimus hamosus_, Haeckel.

_Lychnocanium hamosum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. vii. fig. 9.

Shell pear-shaped, rough, with deep collar stricture. Relative length of the two joints = 1 : 2, breadth = 1 : 3. Cephalis subglobular, with a conical horn of twice the length. Thorax with small, regular, circular pores, and with three prominent ribs, prolonged into three vertical prismatic feet, which are about as long as the shell, parallel or a little convergent towards the distal end, with recurved teeth or hooks at the lateral edges.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.04 long, 0.06 broad.

_Habitat._--Fossil in Barbados.

16. _Dictyophimus tridentatus_, Haeckel.

_Lychnocanium tridentatum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 80, Taf. vii. fig. 4.

Shell smooth, three-sided pyramidal, with deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis subspherical, with a conical horn of the same length, and some small accessory thorns. Thorax tetrahedral, with three smooth hyaline walls, bearing only a single series of small pores on each side of the three prominent ribs, which are prolonged into three strong prismatic curved feet of twice the length, with the convexity external. A group of small pores and a strong triangular tooth at the base of each foot.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.06 long, 0.08 broad.

_Habitat._--Fossil in Barbados.

Subgenus 2. _Lamprotripus_, Haeckel, 1881, Prodromus, p. 432.

_Definition._--Shell spiny or thorny, with prominent spines on the edges of the three thoracic ribs. (Commonly one larger and a few smaller horns or spines on the cephalis.)

{1200}17. _Dictyophimus triserratus_, n. sp. (Pl. 61, fig. 17).

Shell three-sided pyramidal, with slight collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 4. Cephalis small, subspherical, with a large pyramidal horn three times as long. Thorax with much larger, irregular roundish, double-edged pores, and three prominent, serrate ribs, which are prolonged into three pyramidal strongly divergent feet of the same length.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.06 long, 0.09 broad.

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

18. _Dictyophimus bicornis_, n. sp.

Shell thorny, with deep collar stricture. Relative length of the two joints = 2 : 3, breadth = 2 : 3. Cephalis nearly as large as the thorax, subglobular, with numerous small, circular pores, and two divergent pyramidal horns of half the length (a major occipital and a minor frontal horn). Thorax three-sided pyramidal, with larger irregular pores and three serrate ribs, which are prolonged into three prismatic spiny feet of half the length. (Differs from the similar _Dictyophimus sphærocephalus_, Pl. 57, fig. 10, mainly in the double horn and the spinulate feet.)

_Dimensions._--Cephalis 0.05 long, 0.05 broad; thorax 0.08 long, 0.07 broad.

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

19. _Dictyophimus pocillum_, Ehrenberg.

_Dictyophimus pocillum_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. v. fig. 6.

Shell thorny, with distinct collar stricture. Relative length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis nearly spherical, with numerous small conical spines. Thorax flat, three-sided pyramidal with large, irregular, roundish pores, and three strong, widely divergent, spinulate ribs, which are prolonged into three prismatic spinulate feet of the same length.

_Dimensions._--Cephalis 0.03 long, 0.03 broad; thorax 0.15 long, 0.15 broad.

_Habitat._--Fossil in Barbados.

20. _Dictyophimus cienkowskii_, n. sp. (Pl. 60, fig. 1).

_Lamprotripus squarrosus_, Haeckel, 1881, Prodromus et Atlas.

Shell spiny, flatly pyramidal, with slight collar stricture. Relative length of the two joints = 1 : 3, breadth = 2 : 6. Cephalis flat, cap-shaped, three times as long as broad, with numerous bristle-shaped spines three times as long. Thorax also spiny, with irregular, very large, polygonal meshes and thin bars; its three ribs prolonged into three very long and thin, widely divergent, prismatic feet, bearing numerous long spines on the three edges.

_Dimensions._--Cephalis 0.025 long, 0.05 broad; thorax 0.075 long, 0.15 broad.

_Habitat._--North Pacific, Station 250, surface.

{1201}21. _Dictyophimus bütschlii_, n. sp. (Pl. 60, fig. 2).

_Lamprotripus horridus_, Haeckel, 1881, Prodromus et Atlas.

Shell spiny, flatly pyramidal, with deep collar stricture. Relative length at the two joints = 1 : 2, breadth = 1 : 5. Cephalis subspherical, with numerous long, bristle-shaped spines and a larger ramified horn. Thorax also spiny, flatly vaulted, with large, subregular, hexagonal meshes and thin bars; its three spiny ribs prolonged into three very long and thin, prismatic, widely divergent feet, twice to four times as long as the thorax.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.08 long, 0.2 broad.

_Habitat._--South Pacific, Station 284, surface.

22. _Dictyophimus hertwigii_, n. sp. (Pl. 60, fig. 3).

_Lamprotripus spinosus_, Haeckel, 1881, Prodromus et Atlas.

Shell spiny, flatly pyramidal with sharp collar stricture. Relative length of the two joints = 1 : 2, breath = 1 : 5. Cephalis subspherical, with irregular roundish pores, numerous small spines and a large, oblique, prismatic horn of the same length, bearing on its distal end a bunch of small divergent spines. Thorax pyramidal, with larger irregular polygonal pores and thin bars; its three strong, widely divergent ribs spiny, straight, and prolonged into three prismatic slender feet of the same length. Central capsule with three lobes depending into the thorax.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.08 long, 0.2 broad.

_Habitat._--Central Pacific, Stations 270 to 274, surface.

Genus 535. _Tripocyrtis_,[152] n. gen.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, prolonged into three latticed divergent feet on the peristome. Cephalis with an apical horn.

The genus _Tripocyrtis_ has been derived from the preceding _Dictyophimus_ by complete fenestration of the three basal feet, which throughout their whole length become united by complete lattice-work. This genus is closely allied to _Plectaniscus_.

1. _Tripocyrtis plagoniscus_, n. sp. (Pl. 60, fig. 10).

Cephalis subspherical, with large, roundish meshes and a stout, three-sided pyramidal, irregularly branched horn of twice the length. Thorax with a small number of large, irregular, polygonal meshes and three stout curved ribs about as long as the cephalic horn.

_Dimensions._--Cephalis 0.06 long, 0.07 broad; thorax 0.11 long, 0.16 broad.

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

{1202}2. _Tripocyrtis tripodiscus_, n. sp.

Cephalis subspherical, with small, polygonal pores and a large, arborescent, vertical horn of thrice the length, bearing numerous ramified branches. Thorax with three straight, widely divergent ribs, of the same length as the horn, connected by a delicate, arachnoidal framework with irregular, polygonal meshes.

_Dimensions._--Cephalis 0.04 long, 05 broad; thorax 0.12 long, 0.18 broad.

_Habitat._--Central Pacific, Station 269, surface.

3. _Tripocyrtis plectaniscus_, n. sp. (Pl. 60, fig. 9).

Cephalis subspherical, with small roundish pores, and a stout, three-sided pyramidal, denticulate horn of the same length. Thorax with three little divergent and curved ribs, twice as long as the horn, in the upper half with smaller, in the lower half with larger, polygonal, irregular meshes.

_Dimensions._--Cephalis 0.05 long, 0.06 broad; thorax 0.1 long, 0.12 broad.

_Habitat._--Central Pacific, Station 264, surface.

Genus 536. _Sethopilium_,[153] Haeckel, 1881, Prodromus, p. 431.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, which are prolonged into three solid divergent feet on the peristome. Cephalis smooth, without a horn.

The genus _Sethopilium_ differs from its probable ancestral form _Dictyophimus_ by the complete loss of the cephalic horn, and of the collar septum between both joints, which are only separated by the slight external collar stricture.

1. _Sethopilium orthopus_, n. sp. (Pl. 97, fig. 8).

Shell smooth, with sharp collar stricture, Relative length of the two joints = 5 : 4, breadth = 7 : 6. Cephalis large, subspherical, with numerous regular circular pores, twice as broad as the bars. Thorax with three stout, straight, widely divergent ribs, prolonged into three straight pointed feet of the same length. Between every two ribs, in the centre of the collar stricture, a single large triangular mesh, and beyond this three to six rows of smaller irregular meshes.

_Dimensions._--Cephalis 0.05 long, 0.07 broad; thorax 0.04 long, 0.06 broad.

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

2. _Sethopilium cyrtopus_, n. sp.

Shell smooth, with sharp collar stricture. Relative length of the two joints = 4 : 6, breadth = 7 : 11. Cephalis hemispherical, with large irregular roundish pores, four times as broad as the bars. {1203}Thorax with three stout, curved, widely divergent ribs, prolonged into three cylindro-conical, curved feet of twice the length, which are convex in the proximal half, concave in the distal half. Between every two ribs, beyond the collar stricture, two large ovate meshes, and beyond this two rows of smaller irregular meshes.

_Dimensions._--Cephalis 0.04 long, 0.07 broad; thorax 0.05 long, 0.11 broad.

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

3. _Sethopilium macropus_, n. sp. (Pl. 97, fig. 9).

Shell smooth, with slight collar stricture. Relative length of the two joints = 4 : 7, breadth = 6 : 13. Cephalis hemispherical, with irregular double-contoured pores, about as broad as the bars. Thorax with three very stout, carved, widely divergent ribs, prolonged into three curved, cylindrical, very long feet, which are three to four times as long as the shell, and convex on the outside. Between every two ribs, beyond the collar stricture, two large broad meshes, and beyond this two or three rows of smaller meshes.

_Dimensions._--Cephalis 0.04 long, 0.06 broad; thorax 0.07 long, 0.13 broad.

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

Genus 537. _Lithomelissa_,[154] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three free lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. Cephalis with one or more horns.

The genus _Lithomelissa_, containing numerous and widely distributed forms, may like _Dictyophimus_ be regarded as one of the most primitive and ancient forms of Dicyrtida. It differs from the latter by the lateral (not terminal) position of the three thoracic feet, and may be derived either from _Dictyophimus_ (by secondary development of intrapedal network towards the mouth, on the inside of the three feet) or directly from _Tripospyris_ by similar formation of thoracic network beyond the collar stricture, outside the base of the three divergent feet and pierced by the latter. As the species of this genus are numerous, it may perhaps be better to divide it into two or three genera: _Acromelissa_, with a single horn, _Micromelissa_, with two horns, and _Sethomelissa_, with three or more horns.

Subgenus 1. _Acromelissa_, Haeckel, 1881, Prodromus, p. 431.

_Definition._--Cephalis with a single occipital horn.

{1204}1. _Lithomelissa macroptera_, Ehrenberg.

_Lithomelissa macroptera_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. iii. figs. 9, 10.

Shell smooth, with distinct collar stricture. Relative length of the two joints = 4 : 5, breadth = 3 : 4. Cephalis ovate, with a stout, excentric, vertical, pyramidal horn of the same length. Thorax little larger, ovate, truncate. Both joints with very small and scattered pores. Three divergent ribs arise from the base of the cephalic horn, and are prolonged over the major part of the thorax; their under free part arises from the middle part of the thorax and is as long as the horn, straight, pyramidal. Mouth truncate, little constricted.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax 0.05 long, 0.04 broad.

_Habitat._--Fossil in Barbados.

2. _Lithomelissa ehrenbergii_, Bütschli.

_Lithomelissa ehrenbergii_, Bütschli, 1882, Zeitschr. f. wiss. Zool.,
vol. xxxvi. p. 517, Taf. xxxiii. fig. 21_a_, _b_.

_Lithomelissa macroptera_, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 78, Taf. iii. fig. 8.

(?) _Lophophæna capito_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. viii. fig. 6.

(?) _Lophophæna galeata_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 78, Taf. viii. fig. 12.

Shell rough, with distinct collar stricture. Relative length of the two joints = 4 : 2, breadth = 3 : 4. Cephalis ovate, with a stout excentric, oblique, pyramidal horn of half the length. Thorax little shorter, truncate, conical. Both joints with regular circular pores, of the same breadth as the bars. Three divergent conical feet, as long as the cephalis, arise below the collar stricture. Mouth truncate, not constricted.

_Dimensions._--Cephalis 0.08 long, 0.06 broad; thorax 0.04 long, 0.08 broad.

_Habitat._--Central Pacific, Station 265, depth 2900 fathoms; fossil in Barbados.

3. _Lithomelissa macroceras_, n. sp.

Shell spiny, with sharp collar stricture. Relative length of the two joints = 5 : 7, breadth = 5 : 6. Cephalis spherical, with a large pyramidal horn of twice the length. Thorax little longer, ovate, truncate. Both joints with regular circular pores, three times as broad as the bars. Three divergent pyramidal feet, twice as long as the cephalis, arise from the middle part of the thorax. Mouth constricted, half as broad as the thorax.

_Dimensions._--Cephalis 0.05 long, 0.05 broad; thorax 0.07 long, 0.06 broad.

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

4. _Lithomelissa mitra_, Bütschli.

_Lithomelissa mitra_, Bütschli, 1881, Zeitschr. f. wiss. Zool., p. 518,
Taf. xxxiii. fig. 24.

Shell smooth, with distinct collar stricture. Relative length of the two joints = 5 : 4, breadth = 4 : 5. Cephalis ovate, with a slender, straight, vertical, pyramidal horn of the same length. Thorax ovate, {1205}truncate, of about the same size. Both joints with very small and numerous pores, as broad as the bars. Three feet arising from the middle part of the thorax, very small, rudimentary, pyramidal, about as long as broad. Mouth truncate, little constricted.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.04 long, 0.05 broad.

_Habitat._--Fossil in Barbados.

5. _Lithomelissa pycnoptera_, n. sp.

Shell rough, papillate, with slight collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 3. Cephalis small, hemispherical, with very small pores and a slender, straight, conical horn of twice the length. Thorax subconical, with regular circular, hexagonally framed pores, as broad as the bars. From its lower half arise three divergent, very strong feet, pyramidal, as long as the thorax, and three times as long as broad.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.1 diameter.

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

6. _Lithomelissa microstoma_, n. sp.

Shell papillate, with slight collar stricture. Relative length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis small, hemispherical, with a conical horn of twice the length. Thorax subspherical, with subregular circular pores, three times as broad as the bars. From its middle part arise three divergent, stout, conical feet, of half the length, and twice as long as broad. Mouth small, strongly constricted, one-fourth to one-third as broad as the thorax.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.15 diameter.

_Habitat._--Fossil in Barbados.

7. _Lithomelissa amphora_, Stöhr.

_Lithomelissa amphora_, Stöhr, 1880, Palæontograph, vol. xxvi. p. 100,
Taf. iii. fig. 11.

Shell smooth, with sharp collar stricture. Relative length of the two joints = 1 : 5, breadth = 2 : 4. Cephalis small, hemispherical, with a cervical horn of the same length. Thorax ovate, with small regular circular pores, twice as broad as the bars. From its upper half arise three divergent, slender, conical feet, only one-fourth as long. Mouth constricted, with a hyaline peristome, half as broad as the thorax.

_Dimensions._--Cephalis 0.013 long, 0.026 broad; thorax 0.063 long, 0.053 broad.

_Habitat._--Fossil in tertiary rocks of Sicily; Grotte (Stöhr).

Subgenus 2. _Micromelissa_, Haeckel, 1881, Prodromus, p. 433 (_sensu emendato_).

_Definition._--Cephalis with two divergent horns, a superior occipital horn and an inferior frontal horn.

{1206}8. _Lithomelissa thoracites_, Haeckel.

_Lithomelissa thoracites_, Haeckel, 1862, Monogr. d. Radiol., p. 301,
Taf. vi. figs. 2-8.

_Lithomelissa thoracites_, R. Hertwig, 1879, Organism. d. Radiol., p. 76,
Taf. viii. fig. 1.

Shell smooth, with deep collar stricture. Cephalis ovate, with two divergent, slender, conical horns, of about half the length; a major oblique occipital horn on the posterior face, and a minor, nearly horizontal horn above the collar stricture, on the anterior face. Thorax about as large as the cephalis, truncate, ovate. Pores of both joints irregular, roundish, of different sizes. From the upper half of the thorax, below the collar stricture, there arise three slender, conical divergent feet, about as long as the cephalis. Mouth truncate, wide open, not constricted. On the numerous varieties of this common species compare my Monograph, on the structure of the ovate central capsule (enclosed in the cephalis), Hertwig, _loc. cit._

_Dimensions._--Cephalis 0.05 to 0.08 long, 0.04 broad; thorax 0.03 to 0.05 long, 0.05 to 0.07 broad.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

9. _Lithomelissa mediterranea_, J. Müller.

_Lithomelissa mediterranea_, J. Müller, 1858, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 45, Taf. vi. fig. 11.

_Lithomelissa mediterranea_, Haeckel, 1862, Monogr. d. Radiol., p. 302.

Shell smooth, with sharp collar stricture. Relative length of the two joints = 4 : 5, breadth = 4 : 5. Cephalis campanulate, conical, with two divergent small conical horns, a major occipital subvertical horn near the summit, and a minor sub-horizontal frontal horn near the collar stricture. Thorax truncate, ovate, little larger than the cephalis. From its lower part there arise three short conical, divergent feet, scarcely half as long as the cephalis (in Müller's figure one of them is seen shortened, opposite to the frontal horn). Pores irregular, roundish, much smaller in the cephalis than in the thorax. Mouth wide open, not constricted.

_Dimensions._--Cephalis 0.04 diameter, thorax 0.05 diameter.

_Habitat._--Mediterranean (French shore), J. Müller, surface.

10. _Lithomelissa bicornis_, Ehrenberg.

_Lithomelissa bicornis_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 297, Taf. ii. fig. 7.

Shell smooth, with deep collar stricture. Relative length of the two joints = 1 : 3, breadth = 1 : 2. Cephalis hemispherical, with two divergent, stout and straight, pyramidal horns; a larger occipital horn sub-vertical near the summit, and a smaller oblique frontal horn near the collar stricture. Thorax subspherical, twice as large, with larger irregular, roundish pores. From its lower half there arise three divergent curved pyramidal feet of about the same length. Mouth constricted, only one-third as broad as the thorax.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.06 diameter.

_Habitat._--Atlantic, Stations 348 to 353, surface.

{1207}11. _Lithomelissa haeckelii_, Bütschli.

_Lithomelissa haeckelii_, Bütschli, 1883, Zeitschr. f. wiss. Zool., vol.
xxxvi. p. 517, Taf. xxxiii. fig. 23, a, b.

Shell rough, with sharp collar stricture. Relative length of the two joints = 6 : 5, breadth = 6 : 7. Cephalis subspherical, large, with two divergent horns, a very large, oblique pyramidal occipital horn on the summit, and a very small frontal horn on the middle of the forehead. Thorax campanulate, little larger than the cephalis, with regular circular pores of twice the breadth. From the upper part of the thorax, below the collar stricture, there arise three stout, divergent, angular, semi-lunar feet, about as long as the shell. Mouth wide open, not constricted.

_Dimensions._--Cephalis 0.6 long, 0.6 broad; thorax 0.05 long, 0.07 broad.

_Habitat._--Tropical Atlantic, Station 347, depth 2260 fathoms; fossil in Barbados.

12. _Lithomelissa bütschlii_, n. sp. (Pl. 56, fig. 1).

Shell smooth, with slight collar stricture. Relative length of the two joints = 5 : 6, breadth = 4 : 5. Cephalis ovate, large, with two small conical horns, which are opposed nearly horizontally, in the upper part of the cephalis; an anterior frontal and a posterior occipital horn. Thorax ovate, truncate, little larger. Pores of both joints irregular, roundish, of very different sizes. From the middle part of the thorax there arise three short conical divergent feet. (In the figured specimen there were some accessory thorns; in another specimen, found afterwards, the surface was quite smooth, but the two horns and the three feet much larger, half as long as the cephalis.)

_Dimensions._--Cephalis 0.05 long, 0.04 broad; 0.06 long, 0.05 broad.

_Habitat._--Central Pacific, Stations 266 to 274, depth 2350 to 2925 fathoms.

Subgenus 3. _Sethomelissa_, Haeckel, 1881, Prodromus, p. 431.

_Definition._--Cephalis with three, four, or more horns, a primary occipital, a secondary frontal, and one or more accessory parietal horns.

13. _Lithomelissa corythium_, Ehrenberg.

_Lithomelissa corythium_, Ehrenberg, 1875, Abhandl. d.k. Akad. d. Wiss.
Berlin, p. 78, Taf. iii, fig. 12.

Shell smooth, with slight collar stricture. Relative length of the two joints = 4 : 3, breadth = 4 : 5. Cephalis campanulate, with three short conical horns on the summit. Thorax flat and wide. From its upper part below the collar stricture, there arise three divergent, pyramidal feet, fenestrated at the base, about as long as the shell. Mouth wide open. (The specimen figured by Ehrenberg was an incomplete one.)

_Dimensions._--Cephalis 0.04 in diameter, thorax 0.03 long, 0.05 broad.

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

{1208}14. _Lithomelissa decacantha_, n. sp. (Pl. 56, fig. 2).

_Sethomelissa decacantha_, Haeckel, 1881, Prodromus et Atlas.

Shell smooth, with deep collar stricture, and with ten prismatic spines of nearly equal size and similar form. Relative length and breadth of the two joints about equal. Cephalis ovate, in the upper half hyaline, in the lower half with few scattered pores; in the equator with four prismatic horns of the same length, which diverge upwards; three of them are placed in the same meridional planes as the three wings and the three feet of the thorax (one occipital and two parietal); the fourth (frontal) horn is opposed to the occipital. Thorax campanulate, three-edged, with three vertical prominent feet (directed downward) and three horizontal wings, arising from their knees. Mouth wide open, not constricted.

_Dimensions._--Cephalis 0.05 diameter; thorax 0.05 long, 0.06 broad.

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

Genus 538. _Psilomelissa_,[155] Haeckel, 1881, Prodromus, p. 431.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three free lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. Cephalis smooth, without a horn.

The genus _Psilomelissa_ has the same formation of the shell as the nearly allied preceding genus _Lithomelissa_, and may be derived from it by reduction and loss of the cephalic horn. The cephalis is quite bare.

1. _Psilomelissa galeata_, Haeckel.

_Dictyocephalus galeatus_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 289, Taf. vii. fig. 25.

Shell smooth, with sharp collar stricture. Relative length of the two joints = 5 : 3, breadth = 4 : 5. Cephalis ovate, with numerous irregular, roundish pores. Thorax truncate, conical, with a few small pores. From its upper part (below the collar stricture) there arise three thin, bristle-shaped, widely divergent wings, about as long as the cephalis. Mouth widely open.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.03 long, 0.05 broad.

_Habitat._--Western Tropical Pacific, Stations 200 to 225, surface.

2. _Psilomelissa phalacra_, n. sp.

Shell smooth, with deep collar stricture. Relative length of the two joints = 5 : 6, breadth = 4 : 4. Cephalis ovate, hyaline, with few small pores only in the lower third. Thorax cylindrical, truncate, with small irregular, roundish pores. From its upper third there arise below the stricture three {1209}club-shaped, nearly horizontally divergent wings, as long as the thorax. The cephalis and the three feet are similar to those of _Peromelissa phalacra_, (Pl. 57, fig. 11); but the cylindrical thorax with irregularly scattered pores is completely different, and exhibits a truncate, wide open mouth.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.06 long, 0.04 broad.

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

3. _Psilomelissa hertwigii_, Haeckel.

_Lithomelissa hertwigii_, Bütschli, 1882, Zeitschr. f. wiss. Zool., p.
517, Taf xxxiii. fig. 22, _a_, _b_.

Shell rough, with obliterated collar stricture. Length of the two joints = 4 : 4, breadth = 5 : 5. Cephalis hemispherical. Thorax little larger, cylindrical. From its upper half there arise three very strong pyramidal divergent wings, about as long as the shell. Pores of both joints very small and numerous, circular. Mouth truncate, wide open.

_Dimensions._--Cephalis 0.04 long, 0.06 broad; thorax 0.04 long, 0.05 broad.

_Habitat._--Fossil in Barbados.

4. _Psilomelissa calvata_, n. sp. (Pl. 56, fig. 3).

Shell smooth, with sharp collar stricture. Length of the two joints = 7 : 5, breadth = 5 : 6. Cephalis ovate, large, with subregular, circular, double-contoured pores. Thorax smaller, ovate, with very irregular, roundish pores of different sizes. From its upper third there arise three conical, slender, widely divergent spines or wings of the same length. (In fig. 3 the cephalis with the three wings is alone represented.)

_Dimensions._--Cephalis 0.07 long, 0.05 broad; thorax 0.05 long, 0.06 broad.

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

5. _Psilomelissa sphærocephala_, n. sp.

Shell rough, with deep collar stricture. Length of the two joints = 1 : 2, breadth = 1 : 3. Cephalis spherical. Thorax cap-shaped, flat and broad. From its upper half there arise three pyramidal wings, half as long, fenestrated at the base and nearly horizontally divergent. Mouth constricted, half as broad as the thorax.

_Dimensions._--Cephalis 0.03 diameter; thorax 0.06 long, 0.09 broad.

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

Genus 539. _Spongomelissa_,[156] n. gen.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three free lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. Cephalis with one or more horns.

{1210}The genus _Spongomelissa_ differs from its ancestral genus _Lithomelissa_ only in the development of spongy framework in the shell-wall--a very rare production in the #Cyrtoidea# (compare _Peripyramis_, p. 1162, and _Spongocyrtis_, p. 1188).

1. _Spongomelissa spongiosa_, Haeckel.

_Lithomelissa spongiosa_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol.
xxxvi. pp. 519, 539, Taf. xxxiii. fig. 25, _a_, _b_, _c_.

Shell of dense spongy structure, with a deep collar stricture. The subspherical cephalis and the truncate abdomen of nearly equal size, both with irregular delicate spongy framework. Mouth wide open. Cephalis with a large vertical apical and a small oblique frontal horn. Thorax with three very stout, three-sided prismatic widely divergent lateral wings, which are covered with numerous irregularly ramified branches; the spongy framework arises by communication of the delicate branches.

_Dimensions._--Cephalis 0.04 long, 0.05 broad; thorax 0.04 long, 0.06 broad.

_Habitat._--Fossil in Barbados.

Genus 540. _Clathrocanium_,[157] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 829.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three prominent lateral ribs on the thorax, alternating with three large holes (or thoracic gates). Cephalis with a horn.

The genus _Clathrocanium_ is nearly allied to _Dictyophimus_ and _Lithomelissa_, and, together with these two genera, may be regarded as surviving representatives of the oldest and most primitive forms of Dicyrtida. It differs from the latter mainly in the incomplete fenestration of the shell, three large interradial holes remaining between the three perradial thoracic ribs. It may therefore be derived either from _Euscenium_ or from _Tripospyris_ by the development of a terminal lattice-band between the three feet. _Clathrocanium_ may be divided into two different subgenera: _Clathrocanidium_, with simple horn and smooth mouth, and _Clathrocorona_, with fenestrated horn and coronated mouth.

Subgenus 1. _Clathrocanidium_, Haeckel.

_Definition._--Horn of the cephalis simple, not fenestrated. Peristome smooth.

{1211}1. _Clathrocanium squarrosum_, Ehrenberg.

_Clathrocanium squarrosum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 287, Taf. vii. fig. 5.

Cephalis campanulate, with irregular roundish pores and a pyramidal horn of the same length, bearing at the apex three short branches. Length of the two joints 2 : 3, breadth = 2 : 6. Thorax with three simple, prismatic, thin ribs, which are twice as long as the cephalis, separated by large triangular holes and connected only at the distal end by a small triangular ring of delicate lattice-work. Peristome smooth, wide, as broad as the thorax.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.06 long, 0.12 broad.

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

2. _Clathrocanium sphærocephalum_, n. sp. (Pl. 64, fig. 1).

Cephalis spherical, with regular circular pores and a prismatic horn of the same length, with three serrated edges. Length of the two joints = 2 : 3, breadth 2 : 4. Thorax with three broad, triangular, latticed, divergent ribs, which are separated by three large ovate holes (about as large as the cephalis), and connected at the distal end by a broad fenestrated circular ring of regular lattice-work (about six pores in its height). Peristome smooth, constricted, half as broad as the thorax.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.06 long, 0.08 broad.

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

3. _Clathrocanium coarctatum_, Ehrenberg.

_Clathrocanium coarctatum_, Ehrenberg, 1872, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 287, Taf vii. fig. 6.

_Lychnocanium fenestratum_, Ehrenberg, 1860, Monatsber. d. k. preuss.
Akad. d. Wiss. Berlin, p. 767.

Cephalis spherical, thorny, with regular circular pores and a simple pyramidal horn of the same length. Length of the two joints = 2 : 3, breadth = 2 : 5. Thorax with three simple, prismatic, little prominent ribs, which are separated by three large ovate holes (twice as long as the cephalis), and connected below the prominent distal end by a narrow circular ring of delicate lattice-work. Peristome smooth, wide, little narrower than the thorax.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.06 long, 0.1 broad.

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

4. _Clathrocanium triomma_, n. sp. (Pl. 64, fig. 3).

Cephalis spherical, thorny, with regular circular pores, and a slender prismatic horn of twice the length, bearing at its apex three short recurved branches. Length of the two joints = 2 : 4, breadth = 2 : 5. Thorax with three broad prismatic, fenestrated ribs, which are separated by three large {1212}subcircular holes, and below the prominent distal end by a broad, triangular, roundish ring of subregular lattice-work (with square pores). Peristome smooth, about half as broad as the thorax.

_Dimensions._--Cephalis 0.04 long, 0.04 broad; thorax 0.08 long, 0.1 broad.

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

Subgenus 2. _Clathrocorona_, Haeckel, 1881, Prodromus, p. 431.

_Definition._--Horn of the cephalis fenestrated. Peristome on the margin of the basal mouth with a corona of spines.

5. _Clathrocanium diadema_, n. sp. (Pl. 64, fig. 2).

_Clathrocorona diadema_, Haeckel, 1881, Prodromus, p. 431.

Cephalis hemispherical, thorny, with irregular roundish pores, and a large prismatic horn of twice the length, the three edges of which are denticulate and fenestrated, each with a series of square pores. Length of the two joints = 1 : 3, breadth = 2 : 4. Thorax thorny, with three broad fenestrated divergent ribs, which are separated by three large ovate holes (twice as long as the cephalis) and have their prominent distal ends connected below by a broad circular ring of lattice-work (with irregular polygonal small meshes). Peristome wide, two-thirds as broad as the thorax, with a circular corona of small square pores and alternating prominent small teeth.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.07 long, 0.09 broad.

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

6. _Clathrocanium reginæ_, n. sp. (Pl. 64, fig. 4).

_Clathrocorona reginæ_, Haeckel, 1881, Prodromus, p. 431.

Cephalis hemispherical, with irregular roundish pores and a prismatic club-shaped horn of twice the length, the three edges of which are denticulate and fenestrated. Length of the two joints = 1 : 3, breadth = 1 : 4. Thorax thorny, with three broad triangular, fenestrated and nodulated ribs, which are separated by three large ovate holes (twice as long as the cephalis) and have their prominent distal ends connected below by a circular ring of lattice-work. Peristome constricted, as broad as the thorax, with a corona of short spines.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.08 long, 0.12 broad.

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

Genus 541. _Lamprodiscus_,[158] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 831.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three divergent lateral ribs in the wall of the flat, conical, discoidal, or pyramidal thorax. Cephalis with a horn. Peristome smooth, without corona of spines.

{1213}The genus _Lamprodiscus_, and the following nearly allied _Lampromitra_, differ from all preceding Sethopilida in the complete connection of the three thoracic feet by lattice-work, so that they are imbedded in the thorax-wall as prominent ribs and are not prolonged beyond the margin as free feet. The shell is commonly very flat, conical or pyramidal, sometimes nearly discoidal. The margin of _Lamprodiscus_ is simple, smooth.

1. _Lamprodiscus monoceros_, Ehrenberg.

_Lamprodiscus monoceros_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 295, Taf. vii. fig. 2.

Shell smooth, with deep collar stricture. Length of the two joints = 1 : 5, breadth = 1 : 8. Cephalis spherical, hyaline, without pores, with an oblique conical horn of the same length. Thorax flat, campanulate, nearly hemispherical, with convex lateral outlines, and regular hexagonal meshes, increasing gradually in size towards the mouth. Bars very thin. Peristome smooth.

_Dimensions._--Cephalis 0.02 diameter; thorax 0.1 long, 0.16 broad.

_Habitat._--Western Tropical Pacific (Philippine Sea), Station 200, surface.

2. _Lamprodiscus coscinodiscus_, Ehrenberg.

_Lamprodiscus coscinodiscus_, Ehrenberg, 1872, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 295, Taf. vii. fig. 3.

Shell smooth, with sharp collar stricture. Thorax of the same form and structure as in the preceding species, differing from it mainly in the structure of the smooth circular margin, which is composed of a ring of very small square pores. Length of the two joints = 1 : 4, breadth = 1 : 8. Cephalis with small hexagonal pores, without horn or with a short rudimentary horn. Lateral outlines of the campanulate thorax in the upper part concave, in the lower convex.

_Dimensions._--Cephalis 0.02 diameter; thorax 0.08 long, 0.16 broad.

_Habitat._--Tropical Pacific, Stations 206, 224, 266, &c., surface.

3. _Lamprodiscus tricostatus_, n. sp.

Shell smooth with deep collar stricture. Length of the two joints = 1 : 3, breadth = 1 : 7. Cephalis spherical, with an oblique conical horn of twice the length and small circular pores. Thorax flatly conical, twice as broad as high, with straight lateral outline, and regular hexagonal meshes, increasing gradually in size towards the mouth; bars very thin. Peristome or margin of the basal mouth circular, smooth. Very similar to _Theopilium tricostatum_ (Pl. 70, fig. 6), but without abdomen. Differs from the two preceding species mainly in the conical form of the thorax and the less delicate network.

_Dimensions._--Cephalis 0.03 diameter; thorax 0.1 long, 0.2 broad.

_Habitat._--Cosmopolitan, Mediterranean, Atlantic, Indian, Pacific; surface.

{1214}4. _Lamprodiscus lævis_, Haeckel.

_Eucecryphalus lævis_, R. Hertwig, 1879, Organism. d. Radiol., p. 77,
Taf. viii. figs. 6, 6_a_, 6_b._

Shell smooth, with distinct collar stricture. Length of the two joints = 1 : 3, breadth = 1 : 6. Cephalis subspherical, with small circular pores and an oblique conical horn of twice the length. Thorax flat, pyramidal, twice as broad as long, with three strong, straight divergent edges and subregular roundish pores. Peristome smooth.

_Dimensions._--Cephalis 0.025 diameter; thorax 0.08 long, 0.16 broad.

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

Genus 542. _Lampromitra_, Haeckel,[159] 1881, Prodromus, p. 431.

_Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three divergent lateral ribs in the wall of the flat conical or pyramidal thorax. Cephalis commonly with a horn. Peristome with a corona of spines.

The genus _Lampromitra_ differs from the preceding and nearly allied _Lamprodiscus_ only in the development of a dentated peristome, or an elegant corona of teeth around the wide open mouth. It bears therefore to the latter the same relation that _Clathrocorona_ does to _Clathrocanium_.

1. _Lampromitra coronata_, n. sp. (Pl. 60, fig. 7, 7_a_).

Shell flat, conical, with slight collar stricture. Length of the two joints = 1 : 2, breadth = 2 : 7. Cephalis hemispherical, with a conical oblique horn of twice the length, and small subregular hexagonal pores. Thorax with larger, subregular, hexagonal meshes, six to eight times as broad as the bars. Peristome or basal margin of the thorax circular, with a marginal ring of smaller polygonal meshes and a triple coronal of short spines; two external rings of short conical centrifugal spines, and an internal ring of thin centripetal rods (fig. 7_a_). In fig. 7 the shell is seen from below and exhibits very distinctly the internal cross of the collar septum, composed of the four divergent cortinar bars; between the latter descend the four pear-shaped lobes of the central capsule (each containing an oil globule), whilst the apical part of the capsule (with the nucleus) is hidden in the large cap-shaped cephalis.

_Dimensions._--Cephalis 0.03 long, 0.07 broad; thorax 0.06 long, 0.2 broad.

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

2. _Lampromitra quadricuspis_ (Pl. 58, fig. 7).

Shell flat, conical, with sharp collar stricture. Length of the two joints = 1 : 3, breadth = 2 : 10. Cephalis hemispherical, with subregular circular pores and an oblique, conical, occipital horn of twice {1215}the length, bearing three divergent lateral branches, which are directed upwards, and correspond to the three thoracic ribs. Further down, near the collar stricture, a short divergent frontal horn arises. Thorax with irregular roundish pores of different sizes, three to six times as broad as the bars. Peristome with a simple coronal of short, conical, divergent spines, about as long as the diameter of the cephalis.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.06 long, 0.2 broad.

_Habitat._--North Atlantic, Canary Islands, surface.

3. _Lampromitra furcata_, n. sp. (Pl. 58, fig. 8).

Shell flat, conical, with deep collar stricture, very similar in form and structure to the preceding species; differs from it in the shape of the peristome and the armature of the cephalis, which bears a conical, forked, occipital horn of the same length, and a small rudimentary divergent frontal horn. Length of the two joints = 1 : 2, breadth = 1 : 6. The four pores of the collar septum (two larger cardinal and two smaller jugular) exhibit in this species a peculiar asymmetry (fig. 8). The peristome bears a simple coronal of spines as long as the diameter of the cephalis. The major part of them is forked, some irregularly branched.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.06 long, 0.18 broad.

_Habitat._--South Pacific, Station 298, depth 2225 fathoms.

4. _Lampromitra pyramidalis_, n. sp.

Shell flat, pyramidal, smooth, with slight collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 9. Cephalis subspherical, with an oblique pyramidal horn of twice the length, and small circular pores. Thorax with three strong, divergent, straight ribs and three flat triangular sides between them, with subregular hexagonal pores, increasing in size towards the mouth. Peristome with a simple coronal of large and numerous divergent, conical spines, half as long as the shell.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.09 long, 0.18 broad.

_Habitat._--South Atlantic, Station 325, depth 2650 fathoms.

5. _Lampromitra huxleyi_, Haeckel (Pl. 59, fig. 1).

_Eucecryphalus huxleyi_, Haeckel, 1879, Natürl. Schöpfungsgesch., Edit.
vii. Taf. xvi. fig. 9.