10. Cyrtocalpis gromia, n. sp. (Pl. 51, fig. 11).

Shell rough, ovate, very thick-walled, with subregular, circular pores of somewhat variable size. The diameter of the internal, simple, subspherical cavity is five to six times as great as the thickness of the wall. Mouth tubular, cylindrical, very narrow, only one-sixth as broad as the shell.

Dimensions.—Shell 0.16 long, 0.11 broad; mouth 0.02 broad.

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

Genus 530. Mitrocalpis,^[147] Haeckel, 1881, Prodromus, p. 427.

Definition.—Archicorida with a double ovate or ellipsoidal shell, composed of two parallel lattice-plates, which are connected by numerous beams. Apex without horn.

The genus Mitrocalpis and the following closely allied Spongocyrtis differ from the four preceding genera of Archicorida in the complicated structure of the shell-wall, which in the former is double, in the latter spongy. The mouth is in both genera constricted, narrow, and the apex without a horn. Mitrocalpis has been derived probably from Cyrtocalpis in the same way as Peripyramis from Bathropyramis, by development of spines on the surface of the shell, which at equal distances from the latter become connected by branches, thus forming an outer envelope.

1. Mitrocalpis palliata, n. sp.

Shell ellipsoidal, large, one and a third times as long as broad. Inner shell very thin-walled, with irregular, polygonal pores of very variable size and form. From its nodal points there arise numerous bristle-shaped radial beams, about as long as the diameter of the mouth, which are connected at equal distances from the surface by delicate threads, forming the outer enveloping shell. The surface of the latter is smooth. The thin bars of the inner shell are twice to four times as broad as those of the outer. Mouth about one-seventh as broad as the shell, with a short tubular peristome.

Dimensions.—Shell 0.35 long, 0.27 broad; mouth 0.04, distance of both shells 0.037.

Habitat.—Central Pacific, Station 271, surface.

Genus 531. Spongocyrtis,^[148] Dunikowski.

Definition.—Archicorida with a spongy ovate shell, the wall of which is composed of irregular spongy wickerwork. Apex without horn.

The genus Spongocyrtis differs from most other Monocyrtida in the spongy structure of the shell, which is found in only very few other genera of Cyrtoidea, e.g., in Spongopyramis and Spongomelissa. It has been derived either from the similar Cyrtocalpis by development of irregular spongy wickerwork on the surface of the simple lattice-shell; or from Arachnocalpis (Pl. 98, fig. 13) by loss of the peristome.

1. Spongocyrtis montis ovis, Dunikowski.

Shell broad, ovate, rough, spongy, thick-walled; length to the breadth = 4 : 3. Spongy framework very dense and dark, with very small roundish pores. Mouth constricted, with a short tubular peristome, about one-third as broad as the shell.

Dimensions.—Shell 0.35 long, 0.26 broad; mouth 0.08 broad.

Habitat.—Fossil in the Alpine Lias (Schafberg bei Salzburg, Dunikowski).

2. Spongocyrtis arachnoides, n. sp.

Shell ellipsoidal, spiny, spongy, thin-walled; length to the breadth = 3 : 2. Spongy framework loose and delicate, with irregular polygonal meshes and arachnoidal thread-like bars. Mouth constricted, without peristome, about one-fifth as broad as the shell. (Very similar to Arachnocalpis ellipsoides, Pl. 98, fig. 13, but without corona around the mouth.)

Dimensions.—Shell 0.32 long, 0.21 broad; mouth 0.04 broad.

Habitat.—Central Pacific, Station 270, depth 2925 fathoms.

Subfamily 2. Archicapsida, Haeckel, 1881, Prodromus, p. 428.

Definition.—Cyrtocalpida, with the basal mouth of the shell fenestrated (vel Monocyrtida eradiata clausa).

Genus 532. Halicapsa,^[149] Haeckel, 1881 Prodromus, p. 429.

Definition.—Archicapsida with an apical horn.

The genus Halicapsa, and the following closely allied Archicapsa, represent together the small subfamily of Archicapsida, or of those Cyrtocalpida, in which the basal mouth of the simple shell is closed by a lattice plate. This may be the original state of this family, if it is derived from the Circospyrida (Circospyris, Dictyospyris) by loss of the sagittal constriction and the primary ring. But it is also possible that the Archicapsida have been partly derived from the Archicorida by secondary fenestration of the open mouth. The genus Halicapsa may be easily confounded with the similar Ellipsid Lithapium (compare p. 303, Pl. 14, figs. 8-10). The skeleton of both genera may be perfectly similar, the only distinction being the structure of the central capsule, which in Halicapsa is that of the Monopylea, in Lithapium that of the Peripylea.

Subgenus 1. Calpocapsa, Haeckel.

Definition.—Surface of the shell smooth or rough, but not spiny.

1. Halicapsa lithapium, n. sp. (Pl. 97, fig. 6).

Shell pear-shaped, rough, one and a half times as long as broad. Pores subregular, circular, twice as broad as the bars. Basal plate with four larger ovate cortinar pores (two larger cardinal and two smaller jugular), and with six smaller peripheral pores (fig. 6). Horn of the apex three-sided pyramidal, stout, half as long as the shell.

Dimensions.—Shell 0.16 long, 0.1 broad; horn 0.08 long.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

2. Halicapsa triglochin, n. sp. (Pl. 53, figs. 3, 4).

Shell ovate, rough, a little longer than broad. Pores regular, circular, hexagonally framed, of the same breadth as the bars. Basal plate (fig. 4) without larger pores. Horn pyramidal, stout, about half as long as the shell, with three short, horizontally divergent secondary spines at the base (possibly remnants of three original cortinar feet?)

Dimensions.—Shell 0.11 long, 0.09 broad; horn 0.06 long.

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

3. Halicapsa prunoides, n. sp.

Shell pear-shaped, tuberculate, a little longer than broad. Pores irregular, roundish, of different sizes. Basal plate with four larger and six smaller pores. Horn pyramidal, stout, about one-third as long as the shell. (May belong perhaps to the similar Prunoidea Lithapium, compare p. 303 and Pl. 14, figs. 8-10.)

Dimensions.—Shell 0.14 long, 0.12 broad; horn 0.05 long.

Habitat.—Fossil in Barbados.

Subgenus 2. Echinocapsa, Haeckel, 1881, Prodromus, p. 429.

Definition.—Surface of the shell spiny, covered with thorns, papillæ or larger spines.

4. Halicapsa papillata, n. sp.

Shell bottle-shaped, papillate, one and a half times as long as broad. Pores circular, much larger in the middle part than towards the poles. The elevated frames between them bear on the nodal points large blunt conical papillæ. Basal plate without larger pores. Horn three-sided pyramidal, one-third as long as the shell, gradually passing into the slender neck of the bottle.

Dimensions.—Shell 0.22 long, 0.15 broad; horn 0.07 long.

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

5. Halicapsa pyriformis, Haeckel.

Shell pear-shaped, a little longer than broad, covered with numerous short conical spines. Pores subregular, circular, of nearly equal size, twice as broad as the bars. Basal plate with four crossed larger ovate pores (two larger cardinal and two smaller jugular pores). Horn stout pyramidal, scarcely one-fourth as long as the shell.

Dimensions.—Shell 0.16 long, 0.14 broad; horn 0.04 long.

Habitat.—Fossil in Barbados, living in the North Pacific (Kamtschatka)?

6. Halicapsa hystrix, n. sp. (Pl. 53, figs. 5, 6).

Shell pear-shaped, subspherical, a little longer than broad, with scattered stout pyramidal spines about as long as the radius of the shell. Pores subregular, circular, three times as broad as the bars. Basal plate (fig. 6) without larger pores. Horn very large, pyramidal, longer than the shell.

Dimensions.—Shell 0.1 long, 0.09 broad; horn 0.13 long.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

Genus 533. Archicapsa,^[150] Haeckel, 1881, Prodromus, p. 428.

Definition.—Archicapsida without apical horn.

The genus Archicapsa differs from the preceding Halicapsa in the absence of the apical horn, and represents the simplest form among the Monocyrtida clausa, a simple, ovate, or pear-shaped shell without any appendages. The characteristic structure of the basal lattice-plate (with three or four large cortinar pores) makes it probable that Archicapsa has been derived either from Halicapsa, by loss of the horn, or directly from Dictyospyris, by reduction of the sagittal ring and constriction.

1. Archicapsa triforis, n. sp. (Pl. 53, figs. 1, 2).

Shell pear-shaped, smooth, one and a half times as long as broad. Pores subregular, circular, of about the same breadth as the bars. Basal plate (fig. 2) with three very large pores, three times as broad as the others (one odd sternal pore and two paired cardinal pores).

Dimensions.—Shell 0.09 long, 0.06 broad.

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

2. Archicapsa quadriforis, n. sp.

Shell ovate, rough, a little longer than broad. Pores subregular, circular, twice as broad as the bars. Basal plate with four larger ovate cortinar pores (two smaller jugular and two larger cardinal pores).

Dimensions.—Shell 0.12 to 0.15 long, 0.1 to 0.12 broad.

Habitat.—Central Pacific, Station 265 to 268, depth 2700 to 2900 fathoms.

3. Archicapsa nonaforis, n. sp.

Shell pear-shaped, thorny, one and a half times as long as broad. Pores regular, circular, small, hexagonally framed, twice as broad as the bars. Basal plate with nine cortinar pores (three larger alternating with three pairs of smaller pores, as in Pl. 87, fig. 2).

Dimensions.—Shell 0.14 long, 0.09 broad.

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

Section II. DICYRTIDA, Haeckel, 1862, Monogr. d. Radiol., pp. 280, 296.

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, n. fam.

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

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.

Synopsis of the Genera of Tripocyrtida.