104 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Superomarginal plates, 21 to a ray, are broader than high except 

 in the interbrachium, and the dorsal face of the plates is wider than 

 long, forming a raised tumid border to abactinal area. The dorsal 

 face of the plate passes into the lateral face very gradually, so that 

 the edge of the ray is well rounded. Each plate, except the last 

 4 to 6, bears a prominent sharp, sometimes slightly flattened spine 

 with a swollen base. On the first 2 plates the spine is near the 

 inner edge of the plate, but on the third is about twice as far from 

 the inner edge, and from the fourth on stands on the rounded border 

 between the dorsal and lateral faces of the plate, and also gradually 

 moves from the median transverse line to the aboral margin. The 

 spines on the first 2 plates are really homologous with the inner 

 (complete) series of Ps. agassizi^ for near the inner edge of the 

 third and sometimes the fourth plates of the type of rohustus a 

 similar spine occurs, making 2 for each of these plates, as regu- 

 larly occurs throughout the ray in agassizi. This second spine is 

 absent in the cot^^pe. The plates are covered with spaced, circular, 

 slightly squamif orm and convex granules on the dorsal surface at 

 base of ray, these becoming more and more squamiform toward the 

 end of ray. On the lateral face of the plates all the granules are 

 squamiform, with the edge upward. 



Inferomarginals without distinct lateral and ventral faces, but 

 forming a steeply sloping side to ray when viewed from below. 

 The plates are slightly arched, so that the bevel is rounded. Be- 

 ginning with the second or third plate is a row of sharp, prominent, 

 flattened spines (slightly larger than superomarginal) extending 

 nearly to tip of ray. The first 3 to 6 plates bear a similar smaller 

 spine spaced from the lower end of the plate one-fifth to one-third 

 width of plate. Exceptionally a proximal plate bears a small spine 

 midway between the 2 series. The surface of plate is covered with 

 spaced squamules, the edge directed upward, becoming closer and 

 overlapping on the edge of plate. Beyond the proximal third of 

 ray the inferomarginals exceed the superomarginals in height when 

 viewed from the side. 



Terminal plate stouter than in gotoi^ nearly as long as wide, 

 notched on the proximal border, and with 3 short tubercular spines 

 on the end. It is sometimes ovoid in cohtour. 



Actinal intermediate plates extending to ninth inferomarginal or 

 a little over half the length of ray. There is exceptionally an un- 

 paired plate behind the mouth plates, but no odd interradial series. 

 The interradial areas are poorly developed, possibly owing to the 

 small size of the specimen. The plates bear spaced groups of 2 to 6 

 clavate, pulpy papillae. 



Adambulacral plates with an angular furrow margin and an 

 armature consisting of 6 or 7 compressed, blunt furrow spines, the 



