OCR Text |
Show 1884.] SPECIES O F O R E A S T E R. 69 The diplacauthid arrangement of the adambulacral spinulation is obscured by the elongation, in places, of the granules which cover the adjacent plates ; seven short spines, of which the median are a little longer than those to the sides, are developed in the inner row ; in the outer there are ordinarily four, not long, but fairly stout, spines ; the forcipiform pedicellaria is developed between the spines of each plate. The arrangement of the ventral plates can be made out underneath the granules of various sizes and shapes by which they are closely invested; a few valvular pedicellariae can be made out among them. The granules on the inferomarginals are rather more, and those on the superomarginal much more delicate. The poriferous areae are not large, and are sharply separated from one another; three rows extend along the greater part of each side of the arm ; on the sloping sides of the disk a few of the ossicles have spiuiform projections which are bare of granules ; the granulation of the dorsal surface is by no means coarse, and no pedicellariae seem to be developed on it. Madreporic plate an elongated oval. Colour (dry) dead white. Measurements : - R = 68 ; r=25 ; width of arms at base 24. Hab. China. OREASTER DECIPIENS, sp. nov. A species with the closest external and general resemblance to O. chinensis, but distinguished from it by characters to which, in the present condition of our knowledge, we must give the value of specific attributes. Thus, though it is larger than O. chinensis, it is far less richly provided with spines on the marginal plates ; there are more spines in the inner, and as a rule, fewer in the outer row of adambulacral spines. In addition to this the disk is quite flat, while r : R = 1 : 3*4, in place of the much lower ratio of 1 : 2*7, which obtains with 0. chinensis, and the number of marginal plates is much greater. Taking into consideration all these differences it seems that we must regard the specimens as belonging to a different species. R = 3*4 r. Disk not high ; arms rather narrow, tapering regularly. Lophial ossicles without spines, save the apical, which are well developed, and are very prominent on the unarmed disk. There are no spines within the apical region. About 25 marginal plates in either series; both take part in forming the sides of the arms, are pretty stout, a little convex ; only the more distal inferomarginals bear spines, and these are distributed with great irregularity ; they are longer and more prominent than in 0. chinensis; there are no spines at all on the superomarginal plates. Just as in 0. chinensis, the adambulacral spinulation appears in places to be triplacanthid owing to the elongation of the adjacent granules ; it is, however, really of a diplacanthid character. There are 9 spines in the inner row, and they are exceedingly delicate ; none are long, but the median are much longer than the lateral ones. Between each plate stands a forcipiform pedicellaria. |