ii4 



FISHER 



Mouth-plates narrow, the free margin of each being longer 

 than that adjacent to first adambulacral, and the combined 

 plates forming a salient angle into actinostome. Margin of 

 plate with a series of about 15 slender tapering spinules, de- 

 creasing in length from inner to outer end of plate. About 8 

 to 10 of these are more regular and occupy the free actinosto- 

 mial margin, the rest being adjacent to first adambulacral plate, 

 between which and the mouth-plate there is a fairly wide suture. 

 A series of numerous similar spinules stands on edge of suture 

 furrow, and sometimes an incomplete, irregular, intermediate 

 series is present. 



Madreporic body situated about its own diameter from inner 

 edge of superomarginal plates, fairly large, surrounded and par- 

 tially obscured by large paxillae ; striations deep, coarse, irreg- 

 ular, centrifugal. 



Type, No. 21925, U. S. Nat. Mus. Type locality, Alba- 

 tross Station 2862, near north end of Vancouver Island (inside) 

 in 238 fathoms, on gray sand and pebbles. 



This well-marked form has larger superomarginals than any 

 previously described species. I have compared the type with 

 a specimen of L. arcticus (No. 17992, U. S. Nat. Mus., " Sta. 

 21, Cashes Ledge'') having a major radius of 35 mm. In L. 

 arcticus the proximal superomarginal plates are not conspicu- 

 ously larger than those of outer third of ray. They are roundish 

 and resemble large paxillae, but in L. pacijicus the proximal 

 plates are much wider than those of distal half of ray, and the 

 plates decrease regularly in width all along ray. The mar- 

 ginal plates of L. arcticus are shorter, hence more band-like, 

 than in L. pacificus, there being 36 plates to R = 35 mm., 

 while in L. pacijicus, with R 43 mm., there are but 28 to 30 

 plates. On account of the difference in size of the superomar- 

 ginals in the 2 species, the abactinal paxillar area is narrower in 

 L. pacijicus. The actinal interradial areas of L. arcticus are 

 slightly larger than in L. facijicus and the paxillae are more 

 crowded. The present species seems to bring Leptychaster 

 nearer to both Bathybiastcr and Psilastcr, on account of the 

 larger superomarginal plates. There are, of course, no special 

 spines on the marginal plates of any Leptychaster. 



