1884.] SPECIES OF OREASTER. 69 



The diplacanthid arrangement of the aclambulacral spinulation is 

 obscured bj 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 ])edicellari8e can be made 

 out among them. The granules on the inferomarginals are rather 

 more, and those on the superomarginal much more delicate. 



The poriferous arese 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 spiniform projections which are bare of granules ; the granula- 

 tion of the dorsal surface is by no means coarse, and no pedicellarise 

 seem to be developed on it. Madreporic plate an elongated oval. 



Colour (dry) dead white. 



Measurements : — R=68 ; ?-=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 withiu 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 dis- 

 tributed with great irregularity ; they are longer and more prominent 

 than in 0. chinensis ; there are no spines at all on the superomar- 

 ginal 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. 



