Page:Scientific results HMS Challenger vol 18 part 2.djvu/315

Rh 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.

? Haliomma pyriforme, Bailey, 1856, Amer. Journ. Sci. and Arts, vol xxii. p. 1, pl. i. fig. 29.

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.

Definition.— 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.