CHARACTERISTIC DEEP-SEA TYPES. — SEA-URCHINS. 89 
acters derived from. the study of a limited number of specimens, 
both in the fossil and recent species. In the seas of the Jura 
Fig. 348. — Dorocidaris papillata. 4. 
and of the chalk the Cidaride must have been common types 
of sea-urchins. Dorocidaris Blakei (Fig. 349), obtained by 
the “Blake,” is perhaps the most interesting of the recent Cida- 
ride, from the variability of its spines. Before the * Blake" 
dredgings none were known among the recent species showing 
any great or striking variety in the form of the radioles. With 
the exception of some of the species of the genus Goniocidaris, 
the radioles are characterized by their uniformity, while among 
the fossils of the family the variation in shape and size of some 
of the jurassic and eretaeeous species is quite remarkable. If 
the present species had been dredged without its two or three 
