“HYMENASTER LATEBROSUS, n. sp.
Marginal contour substellate; interradial angles sharply indented, the lesser radius being in the proportion of 63.6 per cent.; R=22 millim., r=14 millim. Arm-angle acute; rays broad and subtriangular, with their margins gracefully curved outward. General form depressed; dorsal surface over the radii more or less bombous; radial areas not specially defined. Dorsal membrane continuous up to the margin; lateral fringe narrow, regular, and sharply indented.
Supradorsal membrane fine and semitransparent. Paxillae-spinelets uniformly distributed over the entire area, but presenting no definite order of arrangement. Paxillae with few spinelets, 4 to 5 being the general number. Muscular fibres numerous and closely, though rather coarsely and irregularly, reticulated (inter-crossed). Interspaces filled in with a delicate semitransparent membrane, punctured with spiracula, usually one to a mesh, and consequently rather widely spaced. Oscular orifice comparatively small, the valves lying almost level with the surface of the dorsal membrane.
Ambulacral furrows moderately broad, and subpetaloid in outline, tapering gradually to the extremity along the outer third of the ray, and slightly constricted towards the actinostome. Ambulacral spines 3 in number, short, cylindrical, rapidly tapering to a fine point, and covered with thin membrane. Each series is placed high in the furrow, and very oblique to the median line of the ray; the aboral spinelet is much smaller than the other two, of which the adoral is slightly the longest. Aperture-papillae small and oval or subcircular in form, sometimes expanded laterally to such an extent that the breadth is greater than the length.
Mouth-plates comparatively small and short; keel prominent, having a rhomboid outline when seen from above, and inclined upwards into the mouth-cavity, with rather widely expanded lateral flanges, straight and square in front. Each plate bears two robust secondary spines, one on the middle of its surface, standing in the lateral angle of the rhomb, and another, comparatively smaller and thinner, placed near the adoral extremity. Mouth-spines proper are represented by three small tapering spinelets placed on the lateral margin of each plate.
Actino-lateral spines robust and of moderate length, the 7th to 9th from the mouth being longest. The spines of two adjacent rays do not quite meet in the median interradial line, a little narrow channel or wrinkle of the membrane being maintained between their tips. The spines diminish regularly in length after the angle is passed, until they become microscopic at the end of the ray; they are pointed at their outward extremity; and the web being well indented between gives a serrate appearance to the margin.
Station 157. Lat. 53° 55' S., long. 108° 35' E. Depth 1950 fms.; diatom-ooze.”
(Sladen, 1882: 230-231)
