Page:Scientific results HMS Challenger vol 18 part 1.djvu/460

252 the central capsule) with the outer, extracapsular, cortical shell. But in some species only one medullary shell is enclosed in the central capsule, whilst both other shells lie outside it. In such case the distance between these two cortical shells is much smaller than their distance from the simple internal medullary shell. These forms correspond more to aculeate Rhodosphæræ, whilst the others resemble aculeate Thecosphæræ.

Definition.—Pores of the cortical shell regular, of nearly equal size and similar form; spines on the entire surface (commonly one spine at each nodal-point).

1. Actinomma hexagonium, n. sp.

Cortical shell, as well as both medullary shells, very thin walled, with regular, hexagonal pores and thread-like bars between them. Pores of the outer shell twice as broad as those of the middle, and three times as broad as those of the inner shells. Radial proportion of the three spheres = 1 : 3 : 9; about twenty thin radial beams between them. At each nodal-point of the surface arises one bristle-shaped radial spine, half as long as the radius.

Dimensions.—Diameter of the outer shell 0.22, middle 0.07, inner 0.025; meshes of the cortical shell 0.01; length of the spines 0.05.

Habitat.—Central Pacific, Stations 270 to 274, surface.

2. Actinomma facetum, n. sp.

Cortical shell thick walled, with regular, circular, hexagonally framed pores, three times as broad as the bars. Pores of both medullary shells regular, circular. Radial proportion of the three spheres = 1 : 2 : 4; about forty thin radial beams between them. At each nodal-point of the surface arises one short, three-sided pyramidal, radial spine, about one-third as long as the radius.

Dimensions.—Diameter of the outer shell 0.16, middle 0.08, inner 0.04; cortical pores 0.012, bars 0.004; length of the spines 0.03, basal breadth 0.015.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.

3. Actinomma anthomma, n. sp.

Cortical shell thick walled, with regular, six-lobed pores, twice as broad as the bars. At each nodal-point of the surface is one short conical radial spine, as long as the diameter of the pores; one corresponding to each lobe, and there is therefore around each pore a regular corona of six spines, as in Haliomma lirianthus (Pl. 28, fig. 1b). Both medullary shells with simple, circular, regular pores. Radial proportion of the three spheres = 1 : 2.5 : 7; radial beams between them only six, opposite in pairs in the three dimensive axes.