Perknaster densus, n. sp. (Pl. XCVII. figs. 1 and 2 ; Pl. XCVIII. figs. 11 and 12).
Rays five. R= 51 mm.; r = 16 mm. R>3 r. Breadth of a ray at the base, about 18 mm.; breadth about midway between the disk and the extremity, 7.5 mm.
Disk large and inflated. Rays subcylindrical, broad at the base, and tapering gradually up to the extremity, which is obtusely pointed. Interbrachial arcs distinctly angular. Slight depressions feebly defined are present in the median interradial lines on the abactinal surface of the disk. The actinal surface of the disk is concave.
The whole abactinal and lateral surfaces, extending up to the adambulacral plates, are covered with small plates which bear small compact groups of short, obtusely rounded, equal spinelets; the whole resembling closely crowded paxillae. Between the plates papulae are interspersed, but are rarely visible superficially in consequence of the crowding of the spinulation. No order of arrangement whatever is discernible in the plates either on the abactinal or actinal areas, and no traces of the representatives of marginal plates can be detected.
The armature of the adambulacral plates consists of about three pairs of obliquely placed spinelets, the whole forming a transverse double series of spinelets. The innermost pair are larger than the others, and thickly skin-covered, which gives them a robust and often a subprismatic appearance. The outer spinelets are shorter and more cylindrical, and merge into the general spinulation of the actinal surface. The obliquity of the position of the pairs causes one of the spinelets of the innermost pair to be more prominent into the furrow than its companion. No small inner spinelet is present high up in the furrow, as in Cribrella.
The madreporiform body, which is rather large, is situated about midway between the centre of the disk and the margin, and its surface is marked with fine convoluted striations.
Colour in alcohol, a dirty light purplish brown or ashy grey.
Locality.—Station 149H. Off Cumberland Bay, Kerguelen Island. January 29, 1874. Lat. 48° 45' 0" S., long. 69° 14' 0" E. Depth 127 fathoms. Volcanic mud. Surface temperature 39.8° Fahr.
Remarks.—Perknaster densus is readily distinguished from its ally Perknaster fuscus by the general form, by the densely crowded spinulation, and by the character of the armature of the adambulacral plates.
(Sladen, 1889: 552-553)
