4. Micromelissa microptera, Haeckel.

Shell smooth, with distinct collar stricture. Length of the two joints = 4 : 6, breadth = 3 : 5. Cephalis ovate, with a straight sword-shaped horn of the same length and very small pores, some larger ones above the stricture. Thorax little larger, ovate, nearly hyaline, with very few and small scattered pores. From its uppermost part arise three short conical wings, scarcely half as long as the cephalic horn, little curved and divergent downwards.

Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax 0.06 long, 0.05 broad.

Habitat.—Fossil in Barbados.

5. Micromelissa ventricosa, Haeckel.

Shell rough, with slight collar stricture. Length of the two joints = 1 : 7, breadth = 1 : 5. Cephalis small, hemispherical, with a small conical horn of half the length. Thorax ovate, very large, papillate, with irregular, roundish pores. From its basal part arise three short and stout conical wings at great distances, shorter than the cephalis. (A transition-form to Sethocapsa.)

Dimensions.—Cephalis 0.02 long, 0.022 broad; thorax 0.14 long, 0.11 broad.

Habitat.—Fossil in Barbados.

Genus 553. Peromelissa,^[170] Haeckel, 1881, Prodromus, p. 433.

Definition.—Sethoperida (vel Dicyrtida triradiata clausa) with three divergent solid lateral wings. Cephalis without horn.

The genus Peromelissa differs from the preceding ancestral form, Micromelissa, only in the absence of the cephalic horn, which is lost by reduction.

1. Peromelissa phalacra, n. sp. (Pl. 57, fig. 11).

Shell smooth, with two joints of nearly equal size and similar ovate form. Cephalis in the upper half hyaline, without pores; in the lower half with four remote, transverse rows of irregular, roundish pores, decreasing in size towards the hemispherical summit. Thorax with twelve transverse rows of pores, the upper six rows three to four times as large as the lower six rows. From its upper half diverge almost horizontally three angular club-shaped wings, half as long as the shell.

Dimensions.—Cephalis 0.05 long, 0.06 broad; thorax 0.06 long, 0.05 broad.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

2. Peromelissa psilocrana, n. sp.

Shell smooth, very similar to the preceding species in size and form, but differing from it in the disposition of the irregular, roundish pores, which are irregularly scattered, and in the form of the three wings, which are slender, pyramidal, diverging downwards, and about as long as the entire shell.

Dimensions.—Cephalis 0.07 long, 0.06 broad; thorax 0.07 long, 0.06 broad.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Peromelissa capito, Haeckel.

Shell rough, with two joints of nearly equal size and similar ovate form. Pores irregular, roundish, everywhere scattered. From the upper half of the thorax arise three short conical wings, which are little curved and diverge downwards (scarcely half as long as the breadth of the shell).

Dimensions.—Cephalis 0.07 long, 0.06 broad; thorax 0.07 long, 0.06 broad.

Habitat.—Fossil in Barbados.

4. Peromelissa calva, n. sp. (Pl. 57, fig. 12).

Shell rough, with two ovate joints of somewhat different sizes. Pores irregular, roundish, everywhere scattered. Thorax little larger than the cephalis; from its upper half arise three short conical wings, diverging downwardly or nearly horizontally.

Dimensions.—Cephalis 0.06 long, 0.04 broad; thorax 0.07 long, 0.05 broad.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 554. Sethomelissa,^[171] Haeckel, 1881, Prodromus, p. 431.

Definition.—Sethoperida (vel Dicyrtida triradiata clausa) with three divergent latticed lateral wings. Cephalis with a horn (or a bunch of horns).

The genus Sethomelissa differs from the nearly allied Micromelissa in the fenestration of the three lateral wings, and may be derived either from this genus by development of lattice-work connecting the three wings with the shell, or perhaps from Clathrocanium by closing the mouth.

1. Sethomelissa hymenoptera, n. sp.

Cephalis subspherical, thorny, with a bunch of three divergent, larger apical spines. Thorax pear-shaped, with three broad, triangular, latticed wings, the superior edge of which is a horizontal, straight, and stout spine, nearly as long as the thorax. Pores irregular, roundish.

Dimensions.—Cephalis 0.03 diameter; thorax 0.11 long, 0.08 broad.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 555. Tetrahedrina,^[172] Haeckel, 1881, Prodromus, p. 433.

Definition.—Sethoperida (vel Dicyrtida triradiata clausa) with a three-sided pyramidal thorax, the three edges of which are prolonged into three divergent, solid, terminal feet. Cephalis with a horn.

The genus Tetrahedrina, and the two following nearly allied genera, are distinguished by the possession of three free, divergent, terminal feet, projecting over the latticed mouth of the thorax. Tetrahedrina may be derived directly from Dictyophimus, by development of a horizontal latticed mouth-plate from the middle part of the feet, the lower part of which remains free. This genus, not noticed by Ehrenberg, is similar to his Lithochytris, and common in the Barbados deposits.

1. Tetrahedrina pyramidalis, n. sp.

Shell three-sided pyramidal, smooth, with slight collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 4. Cephalis hemispherical, with small, sparsely disposed pores, and a pyramidal horn of the same length. Thorax with subregular, circular pores and three sharp edges, prolonged into three divergent pyramidal feet of the same length.

Dimensions.—Cephalis 0.03 diameter; thorax 0.12 long, 0.12 broad.

Habitat.—Fossil in Barbados.

2. Tetrahedrina pyriformis, n. sp.

Shell pear-shaped, rough, with distinct collar stricture. Length of the two joints = 2 : 6, breadth = 2 : 5. Cephalis subspherical, with a conical horn of the same length. Thorax with subregular, circular pores, ovate, at the broad base with three pyramidal, widely divergent feet of the same length. (Similar to Lychnocanium tribulus, Ehrenberg, 1875, loc. cit., pl. vii. fig. 1, but with the mouth closed by a lattice-plate.)

Dimensions.—Cephalis 0.04 diameter; thorax 0.12 long, 0.1 broad,

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.

3. Tetrahedrina quadricornis, Haeckel.

Shell pear-shaped, papillate, with slight collar stricture. Length of the two joints = 1 : 5, breadth = 1 : 5. Cephalis subspherical, with a stout conical horn twice the length. Thorax with irregular, roundish, lobulated pores, with three conical, stout, divergent feet at the base, of the same size and form as the cephalic horn.

Dimensions.—Cephalis 0.02 diameter; thorax 0.1 long, 0.1 broad.

Habitat.—Fossil in Barbados.

Genus 556. Sethochytris,^[173] Haeckel, 1881, Prodromus, p. 433.

Definition.—Sethoperida (vel Dicyrtida triradiata clausa) with three terminal latticed feet or hollow, fenestrated, divergent, basal apophyses of the thorax. Cephalis with a horn.

The genus Sethochytris differs from the preceding Tetrahedrina in the fenestration of the three basal feet, which form direct protrusions or evaginations of the three basal corners of the pyramidal shell. It may be derived from Sethopera by centrifugal growth of the basal corners.

1. Sethochytris triconiscus, n. sp. (Pl. 57, fig. 13).

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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).

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 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).