202 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



lae pass through the interspaces. As seen from the coelomic surface, on 

 the basal part of arm and adjacent disk integument, are 3 longitudinal 

 series of large plates, a median and 2 lateral rows, where the large plates 

 are compacted with fewer small connectives and no intervening papulae. 

 The plates are low and form 3 simple kinds of intergrading paxillae. The 

 tabulum is only slightly elevated, and the smallest plates bear from 1 to 8 

 short, bluntly pointed, granulelike spinules. The intermediate plates bear 

 one long, stout, tapering, movable spine and a surrounding ring of 1 to 5 

 sharp spinules of varying length and size, and on the base of the tabulum 

 a circle of short granulelike spinules. The largest of the intermediate 

 plates bear 1 to 3 equally long central spines and 1 to 6 slightly shorter 

 secondary spines. The largest paxillar plates confined to the disk and basal 

 ray usually bear a long, sharp, movable central spine and 4 to 9 equal or 

 subequal spines surrounding it. There is considerable variation as to the 

 length and density of these spines. These paxillae are free of secondary 

 spinelets and bear comparatively few granulelike spinules on the edge of 

 the tabulum. Dorsal spines are largest on the center of the disk, where 

 they are about 3 mm. long and fairly stout. The paxillar armature de- 

 creases rapidly in size distally and beyond the papular areas only the small 

 single-spinuled and granulelike spinule forms are present. The differences 

 between the large, small, and intermediate paxillae are more distinct on 

 the disk and papular areas of the rays than on nonpapular areas. The in- 

 termediate paxillar plates are in the process of forming large paxillar 

 plates bearing the long primary spines. 



Marginal plates of two alternate series. There is no encroaching of 

 the superomarginals upon the abactinal area except far along the rays. 

 Each plate is strongly convex, almost tabulate, bearing 1 or 2, often 3, 

 movable tapering spines, the uppermost usually the largest, equal in length 

 to the combined length of three superomarginal plates. These are sur- 

 rounded by 2 to 7 secondary spines of varying length, less than one third 

 the length of the largest spine. On the remainder of the plate, except for 

 the naked border, are numerous, well-spaced, short, blunt, granulate 

 spinules. The plates of both series have their raised portion separated by 

 shallow, naked channels. The spines of the first and second superomar- 

 ginal plates are shorter than the succeeding ones. 



Inferomarginal plates are slightly wider than superomarginals. The 

 central portion of each plate is elevated to form a transverse spine-bearing 

 ridge. Each ridge bears 2 or 3, often 4, rigid but movable, tapering, 

 pointed subequal, outstanding spines, the central or uppermost the largest. 



