| No long radial main-spines (in addition to the constant short bristles of the shell-surface). | ||||||
| Mouth smooth, | ||||||
| 705. Castanarium. | ||||||
| Mouth dentate, | ||||||
| 706. Castanella. | ||||||
| Long radial main-spines scattered between the short constant bristles of the shell-surface. | ||||||
| Main spines simple. | ||||||
| Mouth smooth, | ||||||
| 707. Castanidium. | ||||||
| Mouth dentate, | ||||||
| 708. Castanissa. | ||||||
| Main spines branched. | ||||||
| Mouth smooth, | ||||||
| 709. Castanopsis. | ||||||
| Mouth dentate, | ||||||
| 710. Castanura. | ||||||
Genus 705. Castanarium,[[322]] Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 5.
Definition.—Castanellida without radial main-spines, with a smooth mouth.
The genus Castanarium is the simplest form of all the Castanellida, and may be regarded as the common ancestral form of this family. The simple spherical shell has a smooth, toothless mouth and no larger radial spines; it is densely studded with the simple, radial bristles, which are common to all Castanellida. The shell therefore is very similar to those species of the Astrosphæride Acanthosphæra, which represent the subgenus Rhapidococcus (compare above, p. [210], Pl. [26], fig. 3); it differs from the latter in the possession of the shell-mouth, which is absent in all Sphæroidea.
1. Castanarium darwini, n. sp.
Pores regular, circular, hexagonally framed, three times as broad as the bars. Radial bristles half as long as the radius.
Dimensions.—Diameter of the shell 0.3 to 0.4, of the pores 0.03.
Habitat.—South Atlantic (east of Patagonia), Station 318, depth 2040 fathoms.
2. Castanarium hookeri, n. sp.
Pores regular, circular, hexagonally framed, twice as broad as the bars. Radial bristles one-third as long as the radius.