290 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



with the valves of regular shape, with a rather small terminal opening 

 and a small but distinct end tooth. These usually have a long stalk, 

 up to about 2.5 mm. in length, which makes them quite conspicuous, 

 though the head scarcely exceeds 0.5 mm. in length. The other form 



Fig. 19. — Apical system of Stylocidaris effluens, new species. In 6 one of the oculars 

 is abnormally divided into several smaller plates. 0x6, 6x4 



(pl. 80, figs. 1-3) is very short stalked; the head, which is about 0.8 

 mm. long, is inclosed in a rather thick, apparently glandular skin; 

 the valves are slender, with irregular serrate crests, and a small more 

 or less irregular terminal opening, sometimes with a fairly distinct 



