Chapter XVII: Section II: DICYRTIDA, Haeckel, 1862, Monogr. d. Radiol., pp. 280, 296 (3)

Shell rough, with deep collar stricture. Length of the two joints = 1 : 8, breadth = 1 : 3. Cephalis spherical, with an oblique pyramidal horn of the same length. Thorax campanulate, conical; its three basal corners prolonged into three divergent, slender, hollow, fenestrated cones, twice as long as the thorax, and ending in a stout pyramidal spine.

_Dimensions._--Cephalis 0.04 diameter, thorax 0.12 diameter, length of the feet 0.2.

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

2. _Sethochytris barbadensis_, Haeckel.

_Lithochytris barbadensis_, Ehrenberg, 1875, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 160, Taf. v. fig. 2.

Shell smooth, with slight collar stricture. Length of the two joints = 1 : 6, breadth = 1 : 4. Cephalis ovate, with a conical horn of half the length. Thorax conical; its base prolonged into three divergent, hollow, fenestrated cones, half as long as the thorax. Pores small, subregular, circular.

_Dimensions._--Cephalis 0.025 diameter, thorax 0.1 diameter, length of the feet 0.05.

_Habitat._--Fossil in Barbados.

{1240}3. _Sethochytris pyramis_, n. sp.

Shell smooth, with slight collar stricture. Length of the two joints = 1 : 8, breadth = 1 : 5. Cephalis ovate, with a conical horn of half the length. Thorax pyramidal, with three sharp edges; its base prolonged into three pyramidal, divergent, hollow, fenestrated feet, nearly as long as the thorax. Pores regular, circular, double-contoured.

_Dimensions._--Cephalis 0.04 diameter; thorax 0.2 diameter, length of the feet 0.15.

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

4. _Sethochytris triangula_, Haeckel.

_Lithochytris triangula_, Bury, 1862, Polycystins of Barbados, pl. xix.
fig. 7.

Shell rough, with obliterated collar stricture (but distinct internal collar septum). Length of the two joints = 1 : 6, breadth = 1 : 3. Cephalis subspherical, with a stout conical horn of the same length. Thorax pear-shaped, inflated; its base prolonged into three divergent, hollow, fenestrated cones, about as long as the thorax. Pores regular, circular.

_Dimensions._--Cephalis 0.03 diameter; thorax 0.09 diameter, length of the feet 0.1.

_Habitat._--Fossil in Barbados.

Genus 557. _Clathrolychnus_,[174] Haeckel, 1881, Prodromus, p. 431.

_Definition._--#Sethoperida# (vel Dicyrtida triradiata clausa), with three vertical, lateral latticed wings stretched between the apical horn and the three terminal feet. The external lattice-work connecting the wings and closing the mouth forms an arachnoidal mantle around the shell.

The genus _Clathrolychnus_ may be derived directly from _Clathrocorys_, by development of an external arachnoidal mantle connecting the three wings and the three feet, and enveloping the whole shell, closing at the same time the basal mouth of the thorax by a fenestrated plate.

1. _Clathrolychnus araneosus_, n. sp. (Pl. 64, fig. 5).

Cephalis subspherical, with irregular, polygonal pores and a large pyramidal horn of twice the length. Length of the two joints = 4 : 9, breadth = 5 : 12. Thorax with three large triangular holes (twice as broad as the cephalis) between the three pyramidal, divergent feet, which at the distal end are connected by a narrow band of network, composed of two or three rows of polygonal pores. The entire pyramidal shell is enveloped by a very delicate web of irregular, polygonal {1241}meshes, closing also the basal mouth. (In fig. 5 the greater part of the web is taken off to demonstrate the large holes of the thorax). Only two feet are visible.

_Dimensions._--Cephalis 0.04 long, 0.05 broad; thorax 0.09 long, 0.12 broad.

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

2. _Clathrolychnus periplectus_, n. sp. (Pl. 64, fig. 6).

Cephalis subspherical, with subregular, circular pores and a pyramidal horn of the same length. Length of the two joints = 1 : 2, breadth = 1 : 3. Thorax with three large elliptical holes between the three pyramidal, divergent feet, which are connected at the distal end by a broad band of network, composed of five to ten rows of polygonal pores. The entire pyramidal shell is enveloped by a very delicate web, which on the sides is composed of subregular, square meshes, and on the closed mouth of polygonal meshes. (In fig. 6 only a part of the web is represented.)

_Dimensions._--0.04 long, 0.05 broad; thorax 0.08 long, 0.14 broad.

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

Family LXIII. #ANTHOCYRTIDA#, n. fam.

_Sethophormida et Sethophænida_, Haeckel, 1881, Prodromus, p. 432, 433.

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

The family #Anthocyrtida#, composed of the Sethophormida and Sethophænida of my Prodromus, comprises those #Cyrtoidea# in which the shell is two-jointed and bears numerous radial apophyses. The two subfamilies differ in the shape of the mouth, which in the Sethophormida is a simple, wide opening; in the Sethophænida closed by a lattice-plate.

Numerous fossil and living forms of Anthocyrtida were described formerly by Ehrenberg in his genera _Carpocanium_ and _Anthocyrtis_. These, however, represent only a small part of the whole family, which exhibits a great variety in the composition of the lattice-work and in the number of radial beams. The number of species here described amounts to one hundred and forty, and these are disposed in fourteen genera (twelve Sethophormida and two Sethophænida).

The Sethophormida may be again divided into two different groups or tribes, the _Sethamphorida_ and _Carpocanida_; in the former the thorax bears numerous radial ribs, enclosed in its wall; in the latter these ribs have disappeared, and only a corona of terminal feet is developed around the mouth. The shell of the former is usually pyramidal, with a widely open mouth; of the latter ovate, with a constricted mouth. The mouth of the thorax becomes perfectly closed in the Sethophænida.

{1242}The majority of the Anthocyrtida may be derived from the Polyspyrida (_Petalospyris_, &c.) by reduction of the cephalis and loss of the sagittal ring, as was suggested by Bütschli (1882, _loc. cit._). But another part may also have arisen from the Tripocyrtida, by interpolation of secondary radial apophyses between the three primary perradial apophyses. The cephalis in this family is developed in all possible degrees, from one of a considerable size to one very much reduced. If it becomes perfectly lost, the Cyrtocalpida arise.

_Synopsis of the Genera of Anthocyrtida._

-------------------------------------------------------------------------
I. Subfamily Sethophormida.
Terminal mouth of the thorax a simple wide opening.
--------------------
Radial ribs thorny (rarely smooth) prolonged into free terminal feet
(cephalis commonly large, with one or more horns).
-------------------------------------------------------------------------
Shell flat, campanulate or nearly discoidal
(cephalis without horn), 558. _Sethophormis_.

Shell ovate, with constricted mouth
(without horn), 559. _Sethamphora_.

{ Meshes of the network simple, 560. _Sethopyramis_.
{
Shell slender { Meshes fenestrated by
pyramidal, with { secondary latticework, 561. _Plectopyramis_.
straight ribs. {
{ Meshes closed by spongy
{ framework, 562. _Spongopyramis_.
-------------------------------------------------------------------------
Radial ribs thorny (rarely smooth) prolonged into free terminal feet
(cephalis commonly large, with one or more horns).
-------------------------------------------------------------------------
Shell not enveloped by arachnoidal network, 563. _Acanthocorys_.

Shell enveloped by arachnoidal network, 564. _Arachnocorys_.
-------------------------------------------------------------------------
No ribs in the thorax. Peristome with free terminal feet.
-------------------------------------------------------------------------
{ { Six feet, 565. _Anthocyrtoma_.
{ Feet {
{ terminal, { Nine feet, 566. _Anthocyrtis_.
Cephalis { without {
well-developed { separate { Twelve or more
with an apical { peristome. { feet, 567. _Anthocyrtium_.
horn. {
{ Feet subterminal, outside the
{ constricted peristome, 568. _Anthocyrtidium_.

Cephalis rudimentary, hidden in the upper
part of the thorax, without horn, 569. _Carpocanium_.
-------------------------------------------------------------------------
II. Subfamily Sethophænida. Terminal mouth closed by a lattice-plate.
-------------------------------------------------------------------------
Thorax with lateral apophyses (four to six or
more wings), 570. _Sethophæna_.

Thorax with terminal apophyses (four to six or
more feet), 571. _Clistophæna_.

{1243}Subfamily 1. SETHOPHORMIDA, Haeckel, 1881, Prodromus, p. 432.

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

Genus 558. _Sethophormis_, Haeckel,[175] 1881, Prodromus, p. 432.

_Definition._--#Sethophormida# (vel Dicyrtida multiradiata aperta) with numerous radial ribs in the wall of the flat and broad campanulate or nearly discoidal thorax. Cephalis also flat and broad, cap-shaped without horn.

The genus _Sethophormis_ comprises a great number of widely distributed and large Dicyrtida, all agreeing in the flat cap-shaped or nearly discoidal form of the thorax, which has constantly a very delicate network, and is pierced by numerous radial beams. Four of these are commonly primary and direct prolongations of the four cortinar rods in the collar septum, whilst the others are secondary or interpolated ribs. _Sethophormis_ may be derived either from the triradial _Lamprodiscus_ by multiplication of the ribs (or interpolation of secondary ribs between the three primary), or from _Halicalyptra_ by development of transverse rods connecting its terminal feet, and forming a ribbed thorax. Corresponding to the number of the ribs, we may distinguish as subgenera (separate genera in my Prodromus, 1881, p. 432) _Tetraphormis_ with four, _Pentaphormis_ with five, _Hexaphormis_ with six, _Octophormis_ with eight, _Enneaphormis_ with nine, and _Astrophormis_ with ten to twenty or more ribs. The cephalis bears no horn, and is usually large, flat, cap-shaped or hemispherical.

Subgenus 1. _Tetraphormis_, Haeckel, 1881, Prodromus, p. 432.

_Definition._--Thorax with four radial ribs opposite in pairs in two meridional planes, perpendicular to one another. Collar septum with four large pores.

1. _Sethophormis cruciata_, n. sp.

Cephalis very large, hemispherical with irregular, delicate network of small square meshes. Thorax flatly campanulate, with delicate, regular network of small hexagonal meshes. All bars very thin, thread-like. Four stout radial thoracic ribs, crossed in pairs, lie in two meridional planes, perpendicular to one another. Very similar to _Sethophormis aurelia_ (Pl. 55, figs. 3, 4), but not so flat, and with only four thoracic ribs. Peristome or margin of the thoracic mouth smooth, circular.

_Dimensions._--Cephalis 0.04 long, 0.08 broad; thorax 0.12 long, 0.36 broad.

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

{1244}2. _Sethophormis medusa_, n. sp.

Cephalis very large, flat, cap-shaped, with irregular, delicate network of polygonal meshes. Thorax flat, campanulate, nearly hemispherical, with delicate, irregular network of small polygonal meshes. All bars very thin, thread-like. Four stout radial thoracic ribs, as in the preceding species. Peristome denticulate.

_Dimensions._--Cephalis 0.03 long, 0.09 broad; thorax 0.15 long, 0.25 broad.

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

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

_Definition._--Thorax with five radial ribs, one of the three primary ribs (the odd occipital rib) being simple, the two others (the paired lateral ribs) forked.

3. _Sethophormis pentalactis_, n. sp. (Pl. 56, fig. 5).

Cephalis large, flat, hemispherical, with subregular, hexagonal pores. Thorax flat, campanulate, nearly hemispherical; also with subregular, hexagonal pores, and with five stout ribs. The three primary ribs of the thorax are complete, and reach the peristome; the two secondary ribs (as basal branches of the two lateral ribs) are incomplete and absent in the distal half of the thorax. Peristome denticulate, with an elegant marginal corona of small square pores and short conical spines.

_Dimensions._--Cephalis 0.03 long, 0.06 broad; thorax 0.1 long, 0.2 broad.

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

4. _Sethophormis asteriscus_, n. sp.

Cephalis large, flat, cap-shaped, with irregular polygonal pores. Thorax flat, campanulate, with subregular, hexagonal pores, and five stout ribs. The marginal distance between the two anterior (lateral) ribs is twice as great as the distance between every two other ribs (the postero-lateral ribs being basal branches of the antero-lateral ribs). Peristome with a double corona of short, conical spines.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.06 long, 0.17 broad.

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

5. _Sethophormis astrodiscus_, n. sp.

Cephalis small, flatly vaulted, cap-shaped with irregular polygonal pores. Thorax very flatly vaulted, nearly discoidal, with subregular hexagonal pores, and five stout ribs. The marginal distance between all five ribs is nearly equal. Peristome denticulate with an elegant corona of small square pores and short conical thorns.

_Dimensions._--Cephalis 0.015 long, 0.035 broad; thorax 0.05 long, 0.2 broad.

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

{1245}Subgenus 3. _Hexaphormis_, Haeckel, 1881, Prodromus, p. 432.

_Definition._--Thorax with six radial ribs (three primary perradial and three secondary interradial beams).

6. _Sethophormis hexalactis_, n. sp. (Pl. 56, fig. 6).

Cephalis large, hemispherical, with irregular, polygonal pores. Thorax flatly campanulate, with subregular, hexagonal pores, and six stout radial ribs; the lateral connected in pairs. (Fig. 6 exhibits the central part of the shell, seen from below.) In the subcircular collar septum the two anterior (jugular) meshes are much smaller than the two posterior (cardinal) meshes. The odd anterior (sternal) rib is opposite to the posterior (caudal) rib. The two paired ribs of each side (antero-lateral or pectoral and postero-lateral or ventral ribs) diverge from one common point. In the specimen figured the left half of the thorax exhibited the two regular ribs, and the right half three, a posterior accessory branch being developed (transition to _Octophormis_). This specimen might indeed be called _Heptaphormis heptalactis_.

_Dimensions._--Cephalis 0.02 long, 0.05 broad; thorax 0.08 long, 0.22 broad.

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

7. _Sethophormis hexagonalis_, n. sp.

Cephalis small, flat, cap-shaped, with small, regular, hexagonal pores. Thorax flatly conical, nearly discoidal, with larger pores of the same form, and six stout, straight, prominent ribs. These arise at equal distances from the six corners of the hexagonal base of the collar septum. Peristome hexagonal, with a corona of short spines.

_Dimensions._--Cephalis 0.015 long, 0.04 broad; thorax 0.06 long, 0.24 broad.

_Habitat._--North Atlantic, Station 354, surface.

Subgenus 4. _Octophormis_, Haeckel.

_Definition._--Thorax with eight radial ribs, four secondary interradial beams being interpolated between the four primary perradial beams of _Tetraphormis_.

8. _Sethophormis octalactis_, n. sp.

Cephalis large, hemispherical, with irregular, polygonal pores. Thorax flatly campanulate, with regular, hexagonal pores, and eight stout, regularly-disposed, radial ribs reaching the margin at equal distances. Four of these correspond to the four primary ribs of _Tetraphormis cruciata_, and exhibit at their base a larger pair of basal pores, surrounded by a semicircular ring (Pl. 70, fig. 5); the other four are secondary, interpolated. Peristome circular, simple.

_Dimensions._--Cephalis 0.03 long, 0.06 broad; thorax 0.1 long, 0.22 broad.

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

{1246}Subgenus 5. _Enneaphormis_, Haeckel, 1881, Prodromus, p. 432.

_Definition._--Thorax with nine radial ribs, three of which are the primary beams, the other six being secondary and interpolated.

9. _Sethophormis rotula_, n. sp. (Pl. 57, fig. 9).

_Enneaphormis rotula_, Haeckel, 1881, Prodromus et Atlas, pl. lvii. fig.
9.

Cephalis very large, flat, cap-shaped, trilobed, with irregular, polygonal network. Horizontal collar-ring stout, hexagonal, with three larger and three alternate smaller sides of half the length. From the middle of the three larger sides arise three horizontal, centripetal, radial beams, which are united in the centre of the collar-septum--the three primary cortinar beams. These are prolonged outside into three centrifugal primary ribs of the thorax. From the six corners of the collar-ring arise six other secondary, thoracic ribs, equal in size and similar in form to the three primary. Each of these nine equal, straight ribs of the thorax is thickened towards the distal end, and bears at equal distances five pairs of opposite (tangential) lateral branches. The opposite branches of the neighbouring spines become united, and lie nearly horizontally in one plane, so that the flat, discoidal thorax is like a nine-angled wheel with nine equally distant spokes and five concentric, nine-angled rings.

_Dimensions._--Cephalis 0.12 diameter, thorax 0.36 diameter.

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

10. _Sethophormis triloba_, n. sp.

Cephalis large, hemispherical, distinctly trilobed, with dense, irregular, polygonal network. From the centre of its top diverge three stout arches or semilunar rods, which are curved downwards, and unite with the three horizontal, radial beams of the collar-septum inside the collar-ring. These three parietal arches of the cephalis are much stronger than in the similar preceding species (Pl. 57, fig. 9), and between them are placed three vaulted bosoms of the cephalis. The collar-ring and the thorax are of the same form as in the preceding, but possess only four concentric, nine-angled rings.

_Dimensions._--Cephalis 0.05 long, 0.08 broad; thorax 0.24 diameter.

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

11. _Sethophormis enneastrum_, n. sp.

Cephalis very large, flat, cap-shaped, with hexagonal base, trilobed, of similar form and structure to the two preceding species. The flat, discoidal thorax has also the same form, with nine stout ribs and five concentric, nine-angled rings; its forty-five large meshes, however, are not so simple {1247}as these (Pl. 57, fig. 9), but are subdivided into irregular, smaller meshes by interpolated radial beams connecting the concentric rings.

_Dimensions._--Cephalis 0.1 diameter, thorax 0.3 diameter.

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

12. _Sethophormis arachnium_, n. sp.

Cephalis very large, flat, cap-shaped, trilobed, with hexagonal base, of the same structure as in the three preceding species. The flat discoidal thorax is also similar, and has the same structure as in the preceding species (Pl. 57, fig. 9); but the number of concentric, nine-angled rings is raised from five to eight, and in its outer part nine secondary radial beams are interpolated between the nine primaries, so that the peristome has not nine but eighteen corners.

_Dimensions._--Cephalis 0.08 diameter, thorax 0.4 diameter.

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

13. _Sethophormis enneactis_, n. sp.

Cephalis small, hemispherical, with small, irregular, polygonal pores. Thorax flatly pyramidal, nearly discoidal, with nine prominent, stout ribs, which are connected by numerous (twelve to sixteen) horizontal, nine-angled rings. In the outer half of the thorax there are nine weaker secondary ribs interpolated between the nine stronger primaries, and eighteen shorter and feebler tertiary ribs between the former and the latter. Peristome denticulated, nine-angled.

_Dimensions._--Cephalis 0.03 diameter, thorax 0.08 long, 0.24 broad.

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

14. _Sethophormis eupilium_, n. sp. (Pl. 56, fig. 9).

Sethopyramis eupilium, Haeckel, 1882, Atlas, pl. lvi. fig. 9.

Craspedilium eupilium, Haeckel, 1878, Manuscript.

Cephalis very small, hemispherical, hyaline, without pores. Thorax flatly pyramidal, with nine concave, triangular faces and nine little curved, stout, radial beams. Between these are interpolated numerous incomplete secondary beams, which are absent in the apical part of the thorax. The radial beams being connected by numerous (thirty to forty or more) horizontal, ring-like threads, a delicate arachnoidal network with small, quadrangular pores is produced. Peristome nine-angled, with a peculiar vertical gallery, composed of four horizontal, parallel, nine-angled rings, which are connected by numerous vertical, parallel bars, therefore with three transverse rows of square pores. This peculiar species is very different from the preceding and may represent a separate genus, _Craspedilium_.

_Dimensions._--Cephalis 0.01 diameter, thorax 0.1 long, 0.25 broad.

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

{1248}Subgenus 6. _Astrophormis_, Haeckel.

_Definition._--Thorax with a variable number of radial ribs (twelve to twenty or more).

15. _Sethophormis aurelia_, n. sp. (Pl. 55, figs. 3, 4).

_Leptarachnium aurelia_, Haeckel, 1879, Manuscript et Atlas.

Cephalis large, nearly hemispherical, with irregular, delicate network of small square meshes. Collar-septum with four large meshes, separated by a cross of four bars, opposite in pairs. Thorax flatly campanulate, with delicate, subregular, hexagonal meshes, and twenty-four prominent radial ribs; four of these are primary or perradial (centrifugal prolongations of the four bars of the collar-septum); four others are interradial or secondary, alternating with the former at angles of 45°; sixteen others are adradial or tertiary, interpolated between the first and second more or less irregularly. In some specimens the disposition of the twenty-four ribs was more regular, in others more irregular, than in the specimen figured (figs. 3, 4). The central capsule (fig. 4) exhibits a flat, cap-shaped part with the nucleus (enclosed in the cephalis), and four large, pear-shaped lobes protruded through the four large collar holes (somewhat deformed in the preparation figured). The wall of the thorax exhibits at the base four larger, nearly semicircular pores, bisected by the four primary thoracic ribs. Peristome with twenty-four indentations (between the prominent distal ends of the twenty-four ribs), often more distinct than in the specimen figured.

_Dimensions._--Cephalis 0.03 long, 0.08 broad; thorax 0.1 to 0.2 long, 0.4 to 0.6 broad.

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

16. _Sethophormis dodecaster_, n. sp. (Pl. 56, fig. 12).

Cephalis small, flatly cap-shaped, with irregular, small, roundish pores. Thorax flatly conical, nearly of the same shape as in the preceding species, but only with twelve prominent ribs; four primary or perradial ribs (as prolongations of the four crossed cortinar bars), and eight adradial ribs interpolated between the former, and arising at some distance from the collar ring. Peristome with twelve prominent pointed lobes (supported by the distal ends of the twelve ribs), and with twelve semicircular bosoms between them. (The specimen figured is young and not fully developed.)

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.1 long, 0.3 broad.

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

17. _Sethophormis umbrella_, n. sp. (Pl. 70, figs. 4, 5).

Cephalis large, flatly cap-shaped, with irregular, small polygonal meshes. Thorax flat, umbrella-shaped, with subregular, hexagonal meshes, and sixteen strong radial ribs. Four of these are perradial, and centrifugal prolongations of the four crossed collar beams; four others are interradial, and {1249}arise, alternating with the former, directly from the horizontal collar ring; eight ribs are adradial or tertiary, and arise in pairs from the four large perradial basal arches of the thorax, which become bisected by the four primary ribs. Peristome irregularly denticulate.

_Dimensions._--Cephalis 0.02 long, 0.06 broad; thorax 0.12 long, 0.32 broad.

_Habitat._--North Pacific (off Japan), Stations 236 to 239, surface.

18. _Sethophormis floscula_, n. sp.

Cephalis small, hemispherical, with subregular, small hexagonal pores. Thorax flatly conical, with larger hexagonal meshes and twenty-four ribs; four of these are perradial and prolongations of the four collar bars; four interradial arise from the collar ring between the former, alternating with them. Each of these eight main ribs gives off two more or less irregular, lateral branches (one at each side), altogether sixteen. The thorax is similar to _Cladarachnium ramosum_ (Pl. 55, fig. 5), whilst the cephalis is quite different. Peristome with twenty-four prominent triangular lobes.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.1 long, 0.4 broad.

_Habitat._--South Atlantic, Station 325, surface.

19. _Sethophormis leptoscenium_, n. sp.

Cephalis very small, spherical, with few small, circular pores. Thorax flatly conical or tent-shaped, with concave lateral outlines, small hexagonal meshes, and numerous (thirty to forty or more) strong, little curved, simple radial ribs. Peristome nearly circular, with a corona of small, irregular, conical spines.

_Dimensions._--Cephalis 0.015 diameter; thorax 0.07 long, 0.26 broad.

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

20. _Sethophormis leptopilium_, n. sp.

Cephalis very small, subspherical, hyaline, without pores. Thorax flatly conical or hat-shaped, with concave lateral outlines, and a very delicate network of small square meshes (similar to _Litharachnium araneosum_, Pl. 55, fig. 8). This is supported by thirty-two curved radial ribs, four of which are primary, four secondary, and the other twenty-four interpolated. Peristome horizontally expanded and little recurved, like the reflexed brim of a hat.

_Dimensions._--Cephalis 0.12 diameter; thorax 0.08 long, 0.24 broad.

_Habitat._--South Pacific, Station 291, depth 2250 fathoms.

Genus 559. _Sethamphora_,[176] n. gen.

_Definition._--#Sethophormida# (vel Dicyrtida multiradiata aperta) with numerous curved ribs in the wall of the ovate thorax, the small mouth of which is constricted. Cephalis without horn.

{1250}The genus _Sethamphora_ differs from the preceding _Sethophormis_, and from the next following ribbed Sethophormida, mainly in the small, more or less constricted mouth; therefore the thorax is more or less ovate, and its ribs curved, with the convexity external. Sethophormis may be divided into two different subgenera, _Dictyoprora_ and _Cryptocephalus_; in the former the cephalis is perfectly free and well developed, in the latter it is more or less hidden in the uppermost part of the thorax (like _Carpocanium_).

Subgenus 1. _Dictyoprona_, Haeckel, 1881, Prodromus, p. 430.

_Definition._--Cephalis large, perfectly free, not hidden in the thorax.

1. _Sethamphora hexapleura_, n. sp.

Shell ovate, smooth, with distinct collar stricture. Length of the two joints = 3 : 11, breadth = 5 : 10. Cephalis large, free, hemispherical, with small circular pores. Thorax truncate, ovate, with six strong curved ribs, and six large triangular meshes between them in the upper half; five smaller pores between every two ribs in the lower half (in three tiers); therefore, together, thirty-six thoracic meshes. Mouth strongly constricted, smooth, only one-third as broad as the thorax.

_Dimensions._--Cephalis 0.03 long, 0.05 broad; thorax, 0.11 long, 0.1 broad.

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

2. _Sethamphora enneapleura_, n. sp.

Shell subovate, smooth, with slight collar stricture. Length of the two joints = 3 : 9, breadth = 4 : 8. Cephalis large, hemispherical, free, with small circular pores. Thorax inflated, ovate, with nine strong curved ribs, which are connected by five transverse circular rings at equal distances. Forty-five rounded, squarish, large meshes between them, in five transverse and nine longitudinal rows. Mouth constricted, smooth, half as broad as the thorax.

_Dimensions._--Cephalis 0.03 long, 0.04 broad; thorax 0.09 long, 0.08 broad.

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

3. _Sethamphora dodecapleura_, n. sp.

Shell urceolate, smooth, with sharp collar stricture. Length of the two joints = 3 : 9, breadth = 5 : 9. Cephalis flat, cap-shaped, free, with twelve ribs, and very small pores between them. Thorax thick-walled, inflated, with subcylindrical cavity, and twelve prominent sharp ribs, alternating with twelve longitudinal rows of very small circular pores (eight pores in each row). Mouth constricted, half as broad as the thorax.

_Dimensions._--Cephalis 0.03 long, 0.05 broad; thorax 0.09 long, 0.09 broad.

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

{1251}4. _Sethamphora mongolfieri_, Haeckel.

_Eucyrtidium mongolfieri_, Ehrenberg, 1854, Mikrogeol., Taf. xxxiv. fig.
18; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 72, Taf. x. fig. 3.

Shell urceolate, smooth, with distinct collar stricture. Length of the two joints = 2 : 9, breadth = 3 : 7. Cephalis campanulate, with eighteen ribs and small pores. Thorax nearly ellipsoidal, with eighteen prominent ribs, and eighteen longitudinal rows of regular circular pores between them (eight pores in each row; therefore 144 pores altogether). Mouth constricted, only one-third as broad as the thorax.

_Dimensions._--Cephalis 0.02 long, 0.03 broad; thorax 0.09 long, 0.07 broad.

_Habitat._--Fossil in Barbados.

5. _Sethamphora costata_, n. sp. Pl. 62, fig. 3.

Shell urceolate, smooth, very similar to the preceding species; also with eighteen longitudinal ribs, but differing in the larger size of the cephalis and its pores, and in the more slender and ovate form of the thorax. Length of the two joints = 5 : 10, breadth = 5 : 8. Pores of the cephalis more numerous. Mouth half as broad as the thorax.

_Dimensions._--Cephalis 0.05 long, 0.05 broad; thorax 0.1 long, 0.08 broad.

_Habitat._--Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms.

6. _Sethamphora serrata_, n. sp.

Shell ovate, spinulate, without external collar stricture. Length of the two joints = 1 : 6, breadth = 2 : 4. Cephalis flat, cap-shaped, with small circular pores. Thorax ovate, truncate, with eighteen serrate longitudinal ribs, alternating with eighteen longitudinal rows of short and broad rather oblong pores (twenty to thirty pores in each row). Mouth strongly constricted, only one-fourth as broad as the thorax.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.12 long, 0.08 broad.

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

7. _Sethamphora ampulla_, Haeckel.

_Eucyrtidium ampulla_, Ehrenberg, 1854, Mikrogeol., Taf. xxxvi. fig. 15;
Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 72, Taf. x. figs. 11, 12.

Shell broad, urceolate, spiny, with sharp collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 5. Cephalis subspherical, with few small pores (in figs. 12_a_ and 12_b_ of Ehrenberg, _loc. cit._, broken off, so that the four pores of the cortinar septum appear). Thorax inflated, bottle-shaped, with twenty prominent, sharply dentate ribs, alternating with twenty longitudinal rows of circular pores (about eight pores in each row). Mouth flat, constricted, one-third as broad as the thorax.

_Dimensions._--Cephalis 0.025 long, 0.03 broad; thorax 0.1 long, 0.14 broad.

_Habitat._--Fossil in Barbados.

{1252}8. _Sethamphora aërostatica_, Haeckel.

_Podocyrtis aërostatica_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 80, Taf. xvi. fig. 4.

Shell broad, urceolate, smooth, with sharp collar stricture. Length of the two joints = 2 : 6, breadth = 3 : 8. Cephalis hemispherical, large, with few pores (broken off in fig. 4_a_ of Ehrenberg, so that the six collar pores appear). Thorax inflated, bottle-shaped, with twenty-two to twenty-four smooth prominent ribs, alternating with the some number of longitudinal rows of small circular pores. Mouth very small, strongly constricted, scarcely as broad as the cephalis, with three short teeth.

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

_Habitat._--Fossil in Barbados.

Subgenus 2. _Cryptocephalus_, Haeckel, 1881, Prodromus, p. 430.

_Definition._--Cephalis more or less hidden in thorax, being partly enveloped by its uppermost part.

9. _Sethamphora microstoma_, n. sp. (Pl. 57, fig. 5).

_Cryptoprora microstoma_, Haeckel, Atlas, pl. lvii., fig. 5.

Shell ovate, smooth, without external collar stricture. Length of the two joints = 1 : 6, breadth = 2 : 4. Cephalis flat, cap-shaped, without ribs, with small circular pores. Thorax ovate, with twenty-four prominent ribs, alternating with deep longitudinal furrows, each of which contains a series of about fifteen small circular pores. Mouth very small, representing a short cylindrical tube, which is only one-eighth as broad as the thorax.

_Dimensions._--Cephalis 0.02 long, 0.04 broad; thorax 0.12 long, 0.08 broad.

_Habitat._--Western Tropical Pacific, Station 220, depth 1100 fathoms.

10. _Sethamphora favosa_, n. sp, (Pl. 57, fig. 4).

_Cryptocephalus favosus_, Haeckel, 1881, Prodromus, p. 430.

Shell ovate, dimply. Length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis subspherical, small, completely hidden in the thickened top of the thorax (but very distinct in the longitudinal section). Thorax ovate, with twenty-five to thirty longitudinal ribs, alternating with the same number of longitudinal furrows, each of which contains ten to twelve circular, hexagonally framed pores. In the smooth wall of the peristome only twelve triangular ribs are visible. Mouth constricted, one-third as broad as the thorax.

_Dimensions._--Cephalis 0.02 diameter; thorax 0.1 long, 0.09 broad.

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

{1253}Genus 560. _Sethopyramis_,[177] Haeckel, 1881, Prodromus, p. 432 (sensu emendato !)

_Definition_.--#Sethophormida# (vel Dicyrtida multiradiata aperta) with numerous straight or slightly curved radial ribs in the wall of the pyramidal thorax. Network simple. Cephalis commonly without horn.

The genus _Sethopyramis_ and the four following genera form together a peculiar small group (Sethopyramida), characterised by the slender pyramidal shell, in the wall of which numerous (six to nine or more) radial ribs are enclosed. These ribs may be regarded as the terminal feet of a _Calpophæna_ or _Halicalyptra_, which become connected by transverse bars. _Sethopyramis_ may be derived also directly from _Patagospyris_ by loss of the primary sagittal ring and reduction of the cephalis.

Subgenus 1. _Sestropyramis_, Haeckel.

_Definition_.--Pyramidal shell with six radial main beams (sometimes also five or seven, as individual varieties).

1. _Sethopyramis scalaris_, Haeckel.

_Cornutella scalaris_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. ii. fig. 1.

Shell smooth, slenderly pyramidal, hexagonal. Cephalis large, subglobular, hyaline, without pores (or with very small and scarce pores). Thorax with six straight (or little curved) stout longitudinal ribs or radial beams, which are connected by twenty to thirty complete, hexagonal, horizontal rings. The large meshes so produced are regular, square, their length and breadth equally and gradually increasing towards the mouth.

_Dimensions_.--Cephalis 0.04 diameter; thorax (with twenty-four transverse rings) 0.4 long, 0.15 broad at the mouth.

_Habitat_.--Fossil in Barbados.

2. _Sethopyramis hexalactis_, n. sp.

Shell thorny, of the same form as, and similar structure to, the preceding species, but differing in the spiny surface and the smaller subglobular cephalis, which bears small circular pores and an oblique conical horn twice the length. The whole surface is covered with short conical thorns.

_Dimensions_.--Cephalis 0.02 diameter; thorax (with twenty transverse rings) 0.25 long, 0.1 broad.

_Habitat_.--Central Pacific, Station 268, depth 2900 fathoms.

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

_Definition._--Pyramidal shell with nine radial main beams (sometimes also eight or ten, as individual varieties).

{1254}3. _Sethopyramis enneactis_, n. sp. (Pl. 56, fig. 7).

_Cephalopyramis enneactis_, Haeckel, 1881, Prodromus et Atlas, pl. lvi.
fig. 7.

Shell smooth, slender, pyramidal. Cephalis large, ovate, with pointed apex, nearly hyaline, with very few and small scattered pores. Thorax very slenderly pyramidal, with straight lateral outlines, and nine stout and straight radial beams, which are connected by fifteen to twenty horizontal complete rings. Meshes subregular, square, simple, without secondary network; their length and breadth equally increasing towards the mouth.

_Dimensions._--Cephalis 0.05 long, 0.03 broad; thorax (with twenty transverse rings) 0.24 long, 0.1 broad at the mouth.

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

4. _Sethopyramis quadrata_, n. sp. (Pl. 54, fig. 2).

Shell smooth, slenderly pyramidal, very similar in form and structure to the preceding species; differing from it in the rudimentary cephalis, which is very small, hemispherical, with few small porules. The three internal cortinar bars of the collar stricture are present; when they become lost this species passes over into _Bathropyramis quadrata_ (Pl. 54, fig. 1).

_Dimensions._--Cephalis 0.01 long, 0.02 broad; thorax (with ten transverse rings) 0.15 long, 0.1 broad at the mouth.

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

5. _Sethopyramis quadratella_, Haeckel.

_Cornutella quadratella_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 68, Taf. ii. fig. 2.

_Litharachnium quadratella_, Bütschli, 1882, Zeitschr. f. wiss. Zool.,
vol, xxxvi. p. 540, Taf. xxxiii. fig. 37.

Shell smooth, broadly pyramidal. Cephalis ovate, small, blunt, hyaline, with very few and small pores (in the figure of Ehrenberg broken off). Thorax broadly pyramidal, with straight lateral outlines, and nine stout and straight radial beams, which are connected by eight to twelve horizontal complete rings. Meshes in the upper half regular, square, in the lower half broad, rectangular (in the tenth transverse row twice as broad as long).

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax (with ten transverse rings) 0.15 long, 0.15 broad.

_Habitat._--Fossil in Barbados.

6. _Sethopyramis trapezoides_, n. sp.

Shell smooth, broadly pyramidal. Cephalis large, ovate, hyaline, without pores; its collar septum exhibits distinctly the four collar pores (two larger cardinal and two smaller jugular pores). {1255}Thorax broad, pyramidal, with slightly concave lateral outlines and nine (sometimes eight or ten) curved ribs, which are connected by eighteen to twenty-four complete transverse rings. The large meshes, so produced, have the form of a parallel trapezoid, and are in the eighth transverse row three times as broad as long. (Differs from _Bathropyramis trapezoides_, Pl. 54, fig. 3, mainly by the possession of a well developed cephalis).

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax (with eighteen rings) 0.32 long, 0.24 broad.

_Habitat._--South Pacific, Station 285, depth 2375 fathoms.

7. _Sethopyramis spinosa_, n. sp.

Shell thorny, slender, pyramidal. Cephalis small, subspherical, with few small pores and a straight, vertical, conical horn twice the length. Thorax with nine straight ribs, which are connected by sixteen to twenty complete transverse nine-angled rings. The large meshes so produced are subregular, square. From each nodal point a short conical spine arises. (Differs from the similar _Bathropyramis spinosa_, Pl. 54, fig. 4, by the development of the cephalis and the simple pointed, unforked spines.)

_Dimensions._--Cephalis 0.03 diameter; thorax (with sixteen rings) 0.2 long, 0.12 broad.

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

8. _Sethopyramis hexagonalis_, n. sp.

Shell papillate, slender, pyramidal. Cephalis small, hemispherical, with a straight conical horn twice the length, and small circular pores. Thorax conical, with slightly convex outlines and nine stout, somewhat curved ribs in zig-zag form, which are connected by ten to twelve interrupted transverse bars. From each nodal point a small conical papilla arises. The large meshes so produced are regular, hexagonal, gradually increasing in size towards the mouth.

_Dimensions._--Cephalis 0.03 diameter; thorax (with twelve transverse rows of meshes) 0.18 long, 0.12 broad.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

9. _Sethopyramis cyclomma_, n. sp.

Shell thorny, slender, pyramidal. Cephalis large, subspherical, with numerous very small circular pores, and a small conical horn of the same length. Thorax similar in form and structure to that of the preceding species; but each hexagonal mesh is provided with a very thin circular hyaline ring (like a diaphragm), so that the openings are not hexagonal, but circular. From each nodal point a short pointed conical or slightly forked spine arises.

_Dimensions._--Cephalis 0.02 diameter; thorax (with ten transverse rows of meshes) 0.18 long, 0.14 broad.

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

{1256}Subgenus 3. _Actinopyramis_, Haeckel.

_Definition._--Pyramidal shell with twelve or more radial beams (commonly twelve to twenty-four, sometimes forty or more).

10. _Sethopyramis dodecalactis_, n. sp.

Shell smooth, slender, pyramidal. Cephalis small, spherical, hyaline, with a short conical horn. Thorax with twelve radial ribs in the upper half, between which twelve others are interpolated in the lower half. These are connected by twenty to twenty-four complete transverse rings. The meshes so produced are subregular, rectangular.

_Dimensions._--Cephalis 0.03 diameter; thorax 0.6 long, 0.2 broad.

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

11. _Sethopyramis bicornis_, n. sp.

Shell spiny, slender, pyramidal. Cephalis small, spherical, hyaline, with two divergent conical horns, the major (occipital) three times and the minor (frontal) twice as long. Thorax slender, pyramidal, campanulate, thorny, with twenty to thirty radial beams, which are little curved, convex in the upper, concave in the lower half, and connected by numerous interrupted transverse bars. Meshes in the upper third rounded, in the lower two-thirds quadrangular, of very different sizes. Surface covered with spinules.

_Dimensions._--Cephalis 0.02 diameter; thorns 0.9 long, 0.4 broad.

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

12. _Sethopyramis maxima_, n. sp.

Shell smooth, slender, pyramidal. Cephalis small, spherical, with few small pores, and a stout, vertical, conical horn twice the length. Thorax very prolonged, conical, with straight lateral outlines and numerous (twenty to fifty) radial beams (in the upper third twelve, in the middle third twenty-four, in the lower third forty to fifty, by interpolation); they are connected by very numerous interrupted transverse bars. Meshes subregular, quadrangular. Surface smooth.

_Dimensions._--Cephalis 0.02 diameter; thorax 1.05 long, 0.45 broad.

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

Genus 561. _Plectopyramis_,[178] Haeckel, 1881, Prodromus, p. 432.

_Definition._--#Sethophormida# (vel Dicyrtida multiradiata aperta) with numerous straight or slightly curved radial ribs in the wall of the pyramidal thorax. Network double, the large primary meshes being fenestrated by fine secondary network. Cephalis commonly without horn.

{1257}The genus _Plectopyramis_ differs from the preceding _Sethopyramis_, its ancestral form, only in the peculiar double fenestration of the shell, the large primary meshes of which are separated by strong bars, and filled up by a very delicate arachnoidal network, composed of small pores and very thin threads between them. This double lattice-work often exhibits a very remarkable regularity. As in the preceding genus, the number of radial ribs is commonly six or nine, rarely twelve to twenty or more.

Subgenus 1. _Hexapleuris_, Haeckel.

_Definition._--Pyramidal shell with six radial main beams (sometimes five or seven in individual varieties).

1. _Plectopyramis magnifica_, Haeckel.

_Polycystina magnifica_, Bury, 1862, Polycystins of Barbados, pl. xi.
fig.

Shell smooth, slender, pyramidal. Cephalis large, ovate, pointed, separated from the thorax by a very deep collar stricture, with few irregular pores. Thorax with six strong and straight radial beams, which are connected by about twenty horizontal, hexagonal rings. The large meshes so produced are regular, square, and filled up by an extremely delicate secondary arachnoidal network, composed of regular square pores (as in Pl. 54, figs. 7, 8).

_Dimensions._--Cephalis 0.06 long, 0.04 broad; thorax (with twenty transverse rings) 0.4 long, 0.12 broad.

_Habitat._--Fossil in Barbados.

2. _Plectopyramis hexapleura_, n. sp.

Shell thorny, slender, pyramidal. Cephalis large, ovate, blunt, with deep collar stricture. Thorax with six strong and straight radial beams, which are connected by numerous (twenty to thirty) interrupted transverse bars. The large meshes so produced are irregular, quadrangular, and filled up by irregular, delicate, secondary network, with small polygonal pores.

_Dimensions._--Cephalis 0.05 long, 0.03 broad; thorax 0.3 long, 0.1 broad.

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

Subgenus 2. _Enneapleuris_, Haeckel.

_Definition._--Pyramidal shell with nine radial main beams (sometimes eight or ten in individual varieties).

{1258}3. _Plectopyramis dodecomma_, n. sp. (Pl. 54, fig. 6).

Shell smooth, slenderly pyramidal, with straight outlines. Cephalis conical, obtuse, with thirty-six small square pores (in nine divergent longitudinal rows, each of four pores). Collar septum (between cephalis and thorax) with four distinct collar pores. Thorax pyramidal, with nine very stout and straight angular radial beams, which are connected by ten to fifteen broad horizontal nine-angled rings. Each of the large regular, square meshes so produced contains a very delicate fenestration, with twelve regular, square pores, separated by two transverse and three longitudinal crossed threads. A very regular and remarkable structure.

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax (with ten rings) 0.2 long, 0.15 broad.

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

4. _Plectopyramis quadratomma_, n. sp.

Shell smooth, slenderly pyramidal. Cephalis large, ovate, hyaline, with few very small basal pores and deep collar stricture. Thorax pyramidal, with straight outline, and nine very stout and straight radial beams, which are connected by fifteen to twenty horizontal nine-angled rings. Each of the large regular, square meshes so produced is filled up by a very delicate arachnoidal network, with very numerous and small square pores (as in the similar _Cinclopyramis infundibulum_, Pl. 54, fig. 7, which differs in the loss of the cephalis).

_Dimensions._--Cephalis 0.05 long, 0.03 broad; thorax (with fifteen rings) 0.32 long, 0.2 broad.

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

5. _Plectopyramis trapezomma_, n. sp. (Pl. 54, fig. 8).

Shell smooth, broadly pyramidal, with concave lateral outlines. Cephalis hemispherical, small, with numerous small, circular pores. Thorax pyramidal, with nine stout, concavely curved radial beams, which are connected by twelve to sixteen horizontal nine-angled rings. The large meshes so produced are in the upper half square, in the lower half parallel trapezoid (in the fifteenth ring three times as broad as long), and filled up by a secondary arachnoidal network, with very numerous and small square pores.

_Dimensions._--Cephalis 0.015 long, 0.025 broad; thorax (with fifteen rings) 0.22 long, 0.2 broad.

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

6. _Plectopyramis polygonomma_, n. sp.

Shell smooth, pyramidal, very similar to the preceding species; differing from it in the irregular shape of the delicate polygonal (not tetragonal) secondary network, filling up the large rectangular meshes. The cephalis is larger, hyaline, pear-shaped, pointed, without pores, with a deep collar stricture. The nine radial beams of the thorax are less concave.

_Dimensions._--Cephalis 0.04 long, 0.03 broad; thorax (with fifteen rings) 0.3 long, 0.22 broad.

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

{1259}7. _Plectopyramis heteromma_, n. sp.

Shell smooth, slenderly pyramidal, with concave outlines. Cephalis very small, subspherical, with a small oblique, conical horn, and very small, scarce circular pores. Thorax with nine stout concavely curved radial beams, which are connected by numerous (thirty to fifty or more) interrupted transverse bars. The large irregular meshes so produced are filled up by irregular, polygonal, delicate lattice-work.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax 0.6 long, 0.3 broad.

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

8. _Plectopyramis serrata_, n. sp.

Shell thorny, slenderly pyramidal, with straight outlines. Cephalis very small, spherical, with a long oblique, conical horn, and very small circular pores. Thorax with nine stout, straight, regularly serrate ribs or radial beams, which are connected by numerous (twenty to thirty or more) interrupted transverse bars. The latter, being crossed by intercalated and interrupted irregular radial beams, produce a subregular secondary network of rectangular meshes of different sizes.

_Dimensions._--Cephalis 0.02 long, 0.02 broad; thorax, 0.3 long, 0.2 broad.

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

9. _Plectopyramis fenestrata_, Haeckel.

_Pyramis fenestrata_, Bury, 1862, Polycystins of Barbados, pl. xxi. fig.
8.

Shell thorny, broadly pyramidal, with straight outlines. Cephalis very small, spherical, hyaline. Thorax with nine stout, spinulate, straight ribs or radial beams, which are connected by ten to fifteen transverse bars, which in the upper half are complete rings, in the lower half interrupted, and crossed by irregularly intercalated radial beams. Meshes therefore irregular, quadrangular. All the bars are thorny.

_Dimensions._--Cephalis 0.01 diameter; thorax 0.2 long, 0.16 broad.

_Habitat._--Tropical Atlantic.

10. _Plectopyramis furcata_, n. sp.

Shell spiny, slenderly pyramidal, with straight outlines. Cephalis small, spherical, with few small pores. Thorax with nine stout and straight spinulate ribs, which are connected by a variable number of irregular interrupted transverse bars; the large quadrangular meshes so produced are filled up by irregular delicate network. The entire surface of the thorax is covered with short forked spines.

_Dimensions._--Cephalis 0.02 diameter; thorax 0.3 long, 0.2 broad.

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

{1260}Subgenus 3. _Polypleuris_, Haeckel.

_Definition._--Pyramidal shell with numerous (twelve or more) radial main beams (commonly twelve to eighteen, sometimes twenty to thirty or more).

11. _Plectopyramis polypleura_, n. sp. (Pl. 56, fig. 8).

Shell smooth, slenderly conical, with straight outlines. Cephalis small, subspherical, with very small dot-like pores, and an oblique conical horn twice the length. Thorax with numerous (twenty to thirty) divergent longitudinal ribs; usually twelve of these radial beams appear as stronger, primary main ribs, and twelve to eighteen other as secondary, feebler, interpolated ribs. They are crossed by numerous (twenty to forty or more) horizontal rings. The large meshes so produced are quadrangular, and partly filled up by a very delicate secondary network, with small square pores.

_Dimensions._--Cephalis 0.03 diameter; thorax 0.36 long, 0.24 broad.

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

12. _Plectopyramis lagena_, n. sp.

Shell smooth, wine-bottle shaped, or slenderly conical-campanulate, with bent outlines, which are concave in the upper, convex in the lower half. Cephalis very small, spherical, hyaline, without pores. Thorax with twenty-four radial ribs, twelve stronger primary, alternating with twelve feebler secondary. They are crossed by interrupted transverse bars. The irregular quadrangular meshes so produced are filled up by a delicate, irregular, secondary network.

_Dimensions._--Cephalis 0.02 diameter; thorax 0.5 long, 0.3 broad.

_Habitat._--South Atlantic, Station 335, depth 1425 fathoms.

Genus 562. _Spongopyramis_,[179] n. sp.

_Definition._--#Sethophormida# (vel Dicyrtida multiradiata aperta) with numerous straight or slightly curved radial ribs in the wall of the pyramidal thorax. Network spongy. Cephalis commonly without horn.

The genus _Spongopyramis_ has arisen from _Sethopyramis_ by development of an irregular spongy framework around the lattice-shell, and is one of the small number of #Cyrtoidea# in which the shell-wall exhibits a spongy structure. In both observed species the cephalis is small, but evident.

{1261}1. _Spongopyramis spongiosa_, n. sp. (Pl. 56, fig. 10).

_Plectopyramis spongiosa_, Haeckel, 1881, Prodromus et Atlas, _loc. cit._

Shell partly or entirely enveloped by spongy framework, slender, pyramidal, with rather straight outlines. Cephalis very small, ovate, hyaline. Thorax with nine very stout and nearly straight ribs, which are connected by fifteen to twenty or more irregular, interrupted transverse bars. The irregular quadrangular meshes so produced are filled up by an irregular secondary network, with meshes of very different size and form. The dense spongy envelope, which in the specimen figured covered only half the shell, was complete in another older specimen.

_Dimensions._--Cephalis 0.015 long, 0.01 broad; thorax 0.4 long, 0.25 broad.

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

2. _Spongopyramis spongoplecta_, n. sp.

Shell entirely enveloped by spongy framework, pyramidal, with straight outlines. Cephalis ovate (twice as large as in the preceding species), with small circular pores. Thorax with twelve stout and straight ribs, which are connected by twenty to twenty-five annular, transverse bars. The subregular square meshes so produced are filled up by irregular, spongy network, which envelops the whole shell more loosely than in _Spongopyramis spongiosa_.

_Dimensions._--Cephalis 0.03 long, 0.02 broad; thorax 0.5 long, 0.2 broad.

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

Genus 563. _Acanthocorys_,[180] Haeckel, 1881, Prodromus, p. 432.

_Definition._--#Sethophormida# (vel Dicyrtida multiradiata aperta) with numerous radial ribs in the wall of the pyramidal thorax, prolonged into divergent terminal feet. Network simple. Cephalis commonly with several horns.

The genus _Acanthocorys_ and the following nearly allied _Arachnocorys_ possess a near relation to the three preceding pyramidal genera, but differ from them in the terminal prolongation of the radial ribs, which are commonly spiny and form a corona of free feet around the mouth of the thorax. The cephalis is usually much larger than in the three preceding genera, and bears a variable number of radial horns. Therefore these two genera are probably older and nearer to the common ancestral form of the Sethophormida than the preceding genera. It may be derived directly from _Dictyophimus_ by interpolation of three secondary (interradial) ribs between the three primary (perradial) ribs.

{1262}Subgenus 1. _Acanthocorallium_, Haeckel.

_Definition._--Thorax with six divergent ribs or radial beams (three primary or perradial alternating with three secondary or interradial).

1. _Acanthocorys hexapodia_, n. sp.

Cephalis large, ovate, with subregular hexagonal pores, and six strong, conical, simple, divergent horns of the same length. Thorax flat, conical, smooth, with six large triangular basal holes, separated by six strong, prismatic, smooth beams, which are connected only near the distal end by a hexagonal ring of delicate, irregular network. Collar septum with three meshes, separated by the three centripetal prolongations of the three primary ribs.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.12 long, 0.24 broad.

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

2. _Acanthocorys pristipodia_, n. sp.

Cephalis large, hemispherical, with irregular, polygonal pores, and numerous (ten to twenty) bristle-shaped, radiating horns, which are conical at the base, and twice as long. Thorax flatly campanulate, thorny, with six strong, serrate or spinulate, divergent, radial ribs, prolonged into six free conical feet of the same length. Meshes of the thorax irregular, polygonal, a corona of six larger ones at the base. Collar septum with four meshes, shaped as in Pl. 56, fig. 6.

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

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

3. _Acanthocorys macropodia_, n. sp.

Cephalis small, subspherical, with irregular, roundish pores and numerous small, bristle-shaped horns. Length of the two joints = 1 : 2, breadth = 1 : 6. Thorax sexangular, pyramidal, with six very long and straight, widely divergent feet, which are prismatic and spiny, and three to five times as long as the breadth of the shell. Only the upper third of the six ribs is connected by irregular, roundish network, with six large triangular holes at the base. Collar septum with four meshes which have the same relation to the six ribs as in _Sethophormis hexalactis_ (Pl. 56, fig. 6).

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

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

4. _Acanthocorys bütschlii_, Haeckel.

? _Clathrocanium ehrenbergii_, Bütschli, 1882, Zeitschr. f. wiss. Zool.,
vol. xxxvi. pp. 514, 539, Taf. xxxii. fig. 18, _a_, _b_.

Cephalis large, subspherical, with numerous small, circular pores and three to six divergent, slender, apical horns. Thorax flatly conical, smooth, not much larger than the cephalis, with six {1263}large, triangular or ovate basal holes between the six ribs. Three of these ribs are primary or perradial, and arise immediately from the collar septum, alternating with three secondary or interradial ribs, which arise more outside. The specimen observed by me exhibited six apical horns, and was more complete than that figured by Bütschli, the six ribs being prolonged over the connecting lattice-girdle into six short, divergent feet.

_Dimensions._--Cephalis 0.06 long, 0.06 broad; thorax 0.08 long, 0.1 broad.

_Habitat._--Fossil in Barbados.

Subgenus 2. _Acanthocoronium_, Haeckel.

_Definition._--Thorax with nine divergent ribs or radial beams, three of which are primary or perradial, the other six secondary or interradial.

5. _Acanthocorys umbellifera_, Haeckel.

_Arachnocorys umbellifera_, Haeckel, 1862, Monogr. d. Radiol., p. 305,
Taf. vi. fig. 12.

Cephalis large, ovate, with subregular, circular pores and numerous divergent, simple spines of different lengths. Thorax flatly conical, with nine strong, divergent ribs, which in the distal half are free, in the proximal half connected by numerous transverse beams, forming irregular polygonal meshes. Dorsal face of the thorax armed with scattered ascending spines.

_Dimensions._--Cephalis 0.05 long, 0.035 broad; thorax 0.05 long, 0.12 broad.

_Habitat._--Mediterranean (Messina); Atlantic, Station 354, surface.

6. _Acanthocorys triloba_, n. sp.

Cephalis large, campanulate, trilobed, with irregular, roundish pores, numerous spines, and a large pyramidal horn on the top, which is connected by three constricted arches with the base of the horizontal collar beams. From the latter arise as centrifugal prolongations three stout, curved, primary ribs of the flatly vaulted thorax, and each of these gives off at the base two opposite, lateral, secondary ribs. These nine ribs are spiny, and connected by irregular, arachnoidal network.

_Dimensions._--Cephalis 0.05 long, 0.07 broad; thorax 0.08 long, 0.18 broad.

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

7. _Acanthocorys enneapodia_, n. sp.

Cephalis large, ovate, with irregular roundish pores, and numerous divergent, ascending spines. Thorax smooth, conical, little larger, with the same network, and nine larger, triangular holes at the base; with nine straight, equally-disposed ribs, which are prolonged into slender feet twice the length. With these latter alternate nine shorter radial spines, arising from the truncate peristome.

_Dimensions._--Cephalis 0.05 long, 0.04 broad; thorax 0.05 long, 0.09 broad.

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

{1264}8. _Acanthocorys macroceras_, n. sp. (Pl. 97, fig. 12).

Cephalis large, hemispherical, spiny, with regular, circular pores, and a very large, cylindrical, vertical horn five times as long as the whole shell. Thorax spiny, campanulate, with irregular, roundish pores and nine strong, curved ribs, prolonged into nine slender, divergent feet twice the length, which are curved, convex in the proximal half and concave in the distal half.

_Dimensions._--Cephalis 0.05 long, 0.08 broad; thorax 0.12 long, 0.2 broad.

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

9. _Acanthocorys furcata_, n. sp.

Cephalis large, subspherical, spiny, with irregular, roundish pores. Thorax flatly conical, thorny, with irregular, polygonal pores, decreasing in size toward the mouth, and with nine straight divergent ribs, which at the peristome are forked and prolonged into eighteen slender, very long, bristle-shaped feet.

_Dimensions._--Cephalis 0.045 diameter, thorax 0.07 long, 0.13 broad.

_Habitat._--South Atlantic, Station 323, depth 1900 fathoms.

Subgenus 3. _Acanthocorythium_, Haeckel.

_Definition._--Thorax with a variable number (ten to twenty or more) radial ribs, prolonged into free terminal feet.

10. _Acanthocorys dodecaster_, n. sp.