Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
Genus 737. Cœlostylus,[[353]] n. gen.
Definition.—Cœlographida with an odd sagittal frenulum on each galea and an outer lattice-mantle, armed with twelve styles (two odd and four paired styles on each valve).
The genus Cœlostylus is characterised by the possession of twelve coronal styles; it is closely allied to Cœlospathis, and differs from this in the development of a new pair of styles on each valve. These are placed between the odd nasal and the odd sagittal style of each valve, they are directed forwards, and may therefore be called "pectoral styles."
1. Cœlostylus bisenarius, n. sp. (Pl. [126], fig. 3a, 3b).
Shell-mantle one and a third times as long as broad; its frontal perimeter pentagonal, with a deep median incision at the base; the two oral sides of the pentagon about as long as the basal odd side, and half as long as the two lateral sides. Sagittal perimeter (fig. 3a) octagonal; the three paired lateral sides of the bilateral octagon about equal, and somewhat shorter than the basal and oral odd sides. Equatorial perimeter rounded square. Nasal odd style of each valve with twelve alternate-cruciate pairs of lateral branches, about twice as long as the two paired pectoral styles (each with four pairs), and the odd sagittal style (with six pairs); the two paired tergal styles bear eight pairs and are longer than the latter, shorter than the nasal style. All styles are more or less curved, divergent, and at the distal end four times forked, bearing a terminal coronet with sixteen spinulate fingers (fig. 3b).
Dimensions.—Length of the shell 4.2, breadth 3.2.
Habitat.—Indian Ocean (Madagascar), Rabbe, surface.
2. Cœlostylus flabellatus, n. sp.
Shell-mantle one and a half times as long as broad, very similar to that of the preceding species. It differs from this mainly in the peculiar form of the twenty-four terminal coronets, which are flabellate and very similar to the terminal branches of Cœlodendrum flabellatum (Pl. [121], figs. 5, 6). I formerly supposed, therefore, that both forms belonged to one and the same species. But though I had no complete specimens of the two species, I was afterwards led to the opinion that one and the same peculiar form of terminal branches is here produced by adaptation to similar conditions in two very different genera. Each coronet is a flat flabellum, placed in a meridian plane, and composed of eight pairs of spinulate branches as figured, loc. cit., in figs. 5 and 6. The cap-shaped distal end of each finger is armed with eight to twelve recurved teeth.