3*74 Verrill, Notes on Radiata. 



usually a cluster of such small plates, wliile the two inner plates of 

 tlie upper series are removed from the margin to the upper surface. 

 Ordinai-ily the alternate marginal plates, of l)oth tlie upper and lower 

 series, bear large conical spines, like those of the back ; the^^e are 

 always placed upon the plates tliat approach the margin, while those 

 that are placed farther back toward the upper and lower surfaces 

 have convex and naked centers, surrounded by a margin of granules. 

 There are about ten or twelve lower marginal plates upon one side of 

 each ray, and eight or nine iip))er ones. The plates of the lower sur- 

 face are nearly regular, polygonal, evenly covered with short, angu- 

 lai', flat-topped granules, and each bears a short, stout, blunt central 

 spine, those near the interradial margin longer and sharper. The 

 interambulacral plates bear an even outer row of blunt, flattened 

 spines or papilhe, one to each plate, which are nearly as long as the 

 spines of the adjacent surface, but much smaller ; and an inner row of 

 very slender spines, which are cylindrical and blunt and rise nearly as 

 high as the others, forming groups of three to five upon each plate. 

 When there are but thi'ee, as is most common, the central one is 

 slightly longer or they are all equal ; when four, as often happens 

 toward the mouth, the inner one is much the shortest ; when five, 

 which rarely occurs, the outer one is also much shorter tlian the 

 middle ones. 



In the largest specimen, the radius of the rays is 2 inches; of disk 

 •95 ; length of largest dorsal spines -30; diameter at l)ase -17 ; length 

 of spines of lower surface -15; diameter -10; length of outer inter- 

 ambulacral S})ines '12 ; diameter '05. Another specimen has the 

 greater radius 1-60; lesser -80 ; with tlorsal spines of the same size. 

 The smallest specimen has the greater radius •!)3 ; lesser -47 ; length 

 of dorsal S])ines -15 ; diameter '08. Color light brownish red, when 



dry. 



This species appears to be not uncommon at La Paz, since there are 

 eight specimens in the present collection. 



Oreaster occidentalis Ven-iii, op. cit., p. 278. 



One large specimen of this interesting, and as yet rare species, was 

 received in this collection. It agrees, in all respects, with those from 

 Panama. 



ECHINOIDEA. 

 Cidaris Thouarsii Vai. ; Ven-iii, op. cit.. p. 294. 



One large specimen, agreeing perfectly with those from Pminma. 



