88 THREE CRUISES OF THE “BLAKE.” 
Pelopatides (Fig. 346) and Ankyroderma! (Fig. 347) seem 
Fig. 346. — Peelopatides confundens. 2. (Théel) 
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 
Fig. 347. — Ankyroderma affine. 8. in shallow water are merely 
dri, gent rag ad specifically distinet 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 watér 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 Cidaridz, 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. 
