88 THREE CRUISES OF THE "BLAKE." 



Paelopatides (Fig. 346) and Ankyroderma l (Fig. 347) seem 



Fig. 347. Ankyroderma affine. 

 (Koren & Danielssen.) 



Fig. 346. Pselopatides confnndens. f . (Th4el.) 



to be the only typical truly deep-sea genera of the orders of 



Apoda and Pedata collected 

 by the " Blake," not before 

 found in the littoral regions, 

 while the other deep-sea spe- 

 cies belonging to genera found 

 in shallow water are merely 

 specifically distinct from the 

 littoral forms, though undoubtedly, like other marine animals 

 capable of living at extreme depths, they have become accus- 

 tomed to their different conditions of existence most gradually, 

 and those which live in deep water have acquired characters and 

 habits somewhat distinct from those dwelling in the more lit- 

 toral regions, but which a close study alone would reveal. 



SEA-URCHINS. 



One of the most common sea-urchins is Dorocidaris papil- 

 lata (Fig. 348), a type having a very wide geographical distribu- 

 tion ; it is found everywhere in the Atlantic, and has even been 

 dredged in the Pacific ; it came up in the dredge often to the 

 exclusion of all other forms. It recalls a cretaceous type common 

 both in Europe and America. As in all the Cidaridae, the shape, 

 proportions, and ornamentation of the spines vary greatly, and 

 an exaggerated importance has frequently been assigned to char- 



1 Ankyroderma affine when alive is of a grayish color, the integument is thin, and 

 the extremities of a lighter hue than the body. 



