Verrill, Notes on liacUata. 281 



face and of the marginal plates increases with age, though not regu- 

 larly, since some specimens of large size have fewer tlian others, which 

 are much smaller. I have not yet seen two specimens that agree in 

 the number of the spines. 



One specimen, Avhich may be considered as representing the average 

 condition of adult specimens, has the following characters. Form 

 pentagonal, with regularly incurved sides and short, broad, rounded 

 rays. Greater radius 3 '3 inches; smaller 2*2. Dorsal surface a little 

 convex. Interambulacral plates, near the mouth, bear five or six flat, 

 blunt, slender spines, forming a single row, the two middle ones long- 

 est ; toward the end of the rays there are but three, of which the 

 middle one is the longest. Outside of these there is a row of very 

 stout, thick, rounded spines, with obtuse ends, arranged one opposite 

 each cluster of the interambulacral spines, those near the mouth larg- 

 est, the size diminishing to the end of the rays, where they become 

 small and more pointed. The ambulacral furrows turn upward at the 

 end of the rays and terminate between the swollen upper plates, be- 

 tween which there is, also, a small plate, bearing a small conical tuber- 

 cle. The lower surface is covered by coarse rounded granulations, 

 that become finer and closer toward the mai-ginal plates, which they 

 completely cover, and bears numerous, regularly arranged, short, stout, 

 blunt, conical spines or tubercles, which also decrease in size from the 

 center to the margin. Among these are scattered many short, stout, 

 oblong, two-lipped pedicellariae, which are more numerous near the 

 center, but vary greatly in number upon the different rays. The lower 

 marginal plates belong chiefly to the ventral surface, except near the 

 end of the rays, where they form more of the margin. There are 

 eight of these to each side of a ray, all are convex, those in the inter- 

 radial spaces being smaller than those toward the end of the rays, 

 except the last one, which is smaller than any other and somewhat 

 triangular. Each of these plates bears a short, stout, conical spine 

 larger than those of the lower surface. The upper marginal plates, 

 which form the greater part of the margin, are somewhat irregular iii 

 number and form, there being either seven or eight upon each side of 

 the rays, of these the four nearest the end of the rays, on each side, 

 are about as long as broad, very convex, the last one largest and swol- 

 len, joining its mate on the other side of the ray. The six or seven 

 plates that occupy the interradial portion of the margin are less con- 

 vex and much broader than long, one or two of them bearing near 

 the lower side a stout conical spine. Each of the four outer plates of 

 the margin, except one of the outermost ones, bears a similar conical 

 spine ; these are mostly larger than those of the lower plates. In the 



