142 



ECniNOIDEA. 



The remaining, smaller, spines of a uniform light brown colour. 

 The secondaries form a definite circlet around each areola and are 

 flattened and blunted ; the tertiaries are finer and more pointed. 



As large as the smaller of these are the large bivalved pedicellarise, 

 which are most numerous in the apical region. The buccal mem- 

 brane is crowded with small spines. 



The test is somewhat flattened, subpentagonal rather than cir- 

 cular ; ambulacra about as wide as in C. papillata ; around each 

 pair of pores a groove ; the pore-areas are nearly as wide as the 

 area between them, in which there are two regular rows of miliaries, 

 with a few smaller tubercles scattered between them. There are 

 eight or nine plates in each interambulacral series. The areolae are 

 not as deep as in C. papillata • they frequently are only separated 

 from one another by a single row of granules ; the tubercles are 

 perforated or faintly crenulated ; the granules which closely cover 

 the plates are more equal in size than in C. papillata. 



The extensive calycinal area differs in the two sexes, for in the 

 female the genital pores are of enormous size, and intrude even on 

 the upper ambulacral plates. The radials are very regularly heart- 

 shaped ; the interradials are large, with a nearly straight inner edge, 

 with sides slightly curved, and the outer edge complete in o > but 

 deeply notched in $ . 



Peristome rather small, considerably smaller than calycinal area. 



Diameter of 



a, b. North of the Hebrides. ' Porcupine ' Exp. 



The two specimens in the Museum are said to be Sir W. Thom- 

 son's types ; they were taken " about 100 miles to the north of 

 the Hebrides." and are by Prof. Agassiz said to have come from a 

 depth of 542 fms. 



3. Cidaris gracilis. 



Porocidaris gracilis, Sladen, Proc. R. Irish Acad. i. (1891) p. 699, 

 pi. xxix. 



Under this name Mr. Sladen has described a single specimen, 

 " probably immature," from 51° 1' N., 11° 50' W., and depth 750 

 fms. Perhaps when a mature specimen is found it will be seen to 

 be only C. pwpurata. 



ECHINOTHURIlDvE (see p. 29). 



Key to the Genera o/Echinothuriido3. 



Vertical muscles divide the coelom into chambers. . 1. Astuexosoma. 

 No vertical muscles dividing the coelom into [p. 143. 



chambers 2. Phormosoma. 



[p. 144. 



