4. Hymeniastrum euclidis, n. sp. (Pl. 43, fig. 13).
Arms one and a half times as long as broad, club-shaped, three times as broad in the oval distal part as in the narrow square proximal part. Patagium complete, enveloping the whole triangular disk, and also the convex ends of the arms, with eight to nine convex chamber-rows.
Dimensions.—Radius of the arms 0.18; breadth at the base 0.025, at the broadest distal part 0.07.
Habitat.—Pacific, central area, Stations 270 to 274, surface.
5. Hymeniastrum pythagoræ, Ehrenberg.
Arms nearly as broad as long, two-thirds as broad at the base as at the truncated distal end. Patagium incomplete, enveloping only the basal half of the arms, with four to five rectilinear parallel chamber-rows. (This form has the greatest resemblance to the figure given by Ehrenberg, loc. cit., but differs by the central disk, which is composed of two concentric rings surrounding the small central chamber; compare above Hymenactura pythagoræ, p. 474.)
Dimensions.—Radius of the arms 0.18; breadth at the base 0.08, at the truncated end 0.12.
Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.
6. Hymeniastrum archimedis, n. sp.
Arms nearly triangular, at the truncated, slightly convex end three times as broad as at the narrow base and one and a third times as broad as long; each arm with six simple chambers. Patagium incomplete, enveloping only the basal half of the arms with three to four convex chamber-rows. (Differs from Rhopalastrum hexagonum, Pl. 43, fig. 7, only by the patagium.)
Dimensions.—Radius of the arms 0.2; breadth at the base 0.07, at the truncated end 0.2.
Habitat.—Pacific, central area, Station 274, surface.
Subgenus 2. Hymenastromma, Haeckel.
Definition.—Arms at the distal end provided with radial spines.
7. Hymeniastrum ternarium, Haeckel.
Arms two and a half times as long as broad, three times as broad at the truncated end as at the narrow base, with a strong, conical, radial spine at the end. Patagium incomplete, enveloping only the basal half of the arms, with three to four convex chamber-rows.
Dimensions.—Radius of the arms (without terminal spine) 0.02; breadth at the base 0.025, at the broadest terminal part 0.08.
Habitat.—Fossil in the rocks of Barbados.
