136 NATURAL HISTORY BULLETIN 



The half areas are long elliptical, pointed distally and di- 

 vergent, united at two places by narrow cross-rows of papulae. 



The superomarginal plates are small, narrow, convex above, 

 angular below, alteraating irregularly with the lower series. The 

 surface is evenly covered with very small, acute spinuliform 

 granules, similar to those of the adjacent parapaxillae. Each 

 bears one large, outspreading, terete, evenly tapered, very acute 

 spine, some of them 15""" long, or as long as the width of the ray 

 at base. They have no secondary basal spines. Those on the 

 first three interradial plates are much smaller than most; the 

 first one is smallest. The fourth and fifth are largest; beyond 

 that they decrease regularly. 



The same arrangement, as to size, holds good for the infero- 

 marginal spines, which are of similar length, but rather more 

 slender. But these last have a group of three to five unequal 

 smaller sized spines below them, one of which may be half as 

 long as the primary spine. A row of similar acute spines ex- 

 tends along both the transverse under margins of the plate, two 

 or three in each row, proximally. The rest of the surface is cov- 

 ered with small, erect, acute spinules. Close to its inner end 

 there is often one (sometimes two) small, low, papilliform pedi- 

 cellariae, with six to eight small convergent valves. 



The interactinal plates are in three chevron-like rows. The 

 first forms a rather long row, next the adambulacrals ; each half 

 has six or seven plates. Each plate bears one or two slender 

 spines, and usually a papillose, elliptical pedicellaria, with twelve 

 to sixteen incurved papillae. These often cover more than half 

 the plate. Others of similar size and form occur in the sutures 

 between two plates. 



The adambulacral plates have a prominent, widely curved or 

 often nearly semicircular inner edge on which there is a regular 

 row of about 10 to 12 slender graded spines ; this row is contin- 

 ued on the adoral and aboral edges by about six to eight much 

 smaller spines or spinules. The actinal surface is concave and 

 bears usually two long, rather slender spines, which on the prox- 

 imal plates become more and more unequal, the outer spine be- 

 coming shorter and smaller, until on the basal three or four 

 plates it is reduced to a rudimentary condition and may entirely 



