190 NATURAL HISTORY BULLETIN 



Plate iii ; figure 4. Plate xi ; figure 5. Details. Plate xiii ; fig- 

 ures l-lo. Details. 



The type of this species, in the Museum of Comp. Zoology, is 

 small and doubtless quite young. Some specimens obtained 

 later are rather larger, but none appear to be adult. 



Radii of the type 10"^^ and 27°^"^ ; ratio, 1 :2.7 ; marginal plates 

 fifteen on each ray. 



The median radial row of dorsal plates is slightly differenti- 

 ated, the plates having more hexagonal bases, with shorter lobes, 

 and therefore more closely united ; they have no papular pores 

 between them ; near the base of the rays they have a few smaller 

 plates between them, and such secondary plates also occur on the 

 disk. 



The spinules of the dorsal plates are slender, rough, divergent, 

 but not fasciolated; the central spinules are longer and stouter 

 than the others. 



The superomarginal plates are closely covered above with short 

 or granule-like spinules, which grade into slender spinules lat- 

 erally, forming rudimentary fascioles, and become longer on the 

 lower side. 



The inf eromarginals are more convex or swollen ; they are cov- 

 ered with small sharp spinules, and also bear an oblique row of 

 two to four or more slender, acute spines, situated near the 

 distal margin, and usually appressed, so as to be directed dis- 

 tally. 



The proximal interactinal plates are roundish or subpolygonal, 

 rather crowded, tesselated or overlapping by their edges, with no 

 evident fascioles between them. They are covered with slender, 

 acute, divergent spinules. They have about three or four di- 

 vergent row^s or chevrons with one unpaired plate in each row, 

 except the first. A single row extends on the rays, beyond the 

 disk. 



The adambulacral plates are decidedly oblique, transversely 

 elongated proximally, with the inner end angular and projecting 

 into the groove. There are about five slender divergent spines 

 in a row along the angular margin. The actinal surface is cov- 

 ered with a divergent cluster of small, slender spinules, similar 

 to those of the interactinal plates. About ten proximal plates 



