10 DOROCIDARIS BLAKEI. 



Blakei in the shape of the plates of the abactinal system (PL II. Fig. 17). 

 The ocular plates are in contact with the extremities of the large anal plates 

 inserted between the genital plates ; the other plates of the anal system are 

 of a more uniform size than in the other species of the genus. In a speci- 

 men measuring 50 mm. in diameter, there are 7-8 primary interambulacral 

 plates ; these are covered by a comparatively coarse, irregularly arranged 

 secondary granulation. The poriferous zone is somewhat flexuous, the fur- 

 rows more distant, and the median ambulacra] granulation finer, than in 

 the other West India species of the genus. The ambulacral papilla? and 

 those at the base of the primary radioles of D. Bartletti are nearly of uni- 

 form size; in D. papillata, those surrounding the radioles are somewhat 

 larger, and in D. BMcei they are still more different, being comparatively 

 much wider and flatter than the narrow ambulacral papillae. 



♦Dorocidaris Blakei A. Aa 



Dorocidaris Blakei A. Ah. Bull. M. C. Z., V., No. !), p. 185, PI. IV., 1878. 

 Dorocidaris Blakei A. Aa Hull. M.C.Z., VIII., No. 2, p. 7n, 1880. 



Oil' Havana, 17">-45i> fathoms. 



Santa Cruz to Barbados, 163 270 fathoms. 



PI. /., PI. II Figs. 1-15. 



This species ( PI. 1.) is perhaps the most interesting of the recent Cidaridae. 

 Thus far the living Cidaridae known have not shown any great or striking 

 variety in the form of the radioles. With the exception of some of the 

 recent species of the genus Gomocidaris, the radioles as a whole arc charac- 

 terized by their great uniformity, while among the fossils of the family the 

 greal variation in the shape and size of the radioles of some of the Jurassic 

 and Cretaceous species is most remarkable. In the description of species of 

 the recent Cidaridae, it has not been unusual to lay great stress upon the 

 differences noticed in the shape and ornamentation of the radioles. Com- 

 parative studies of recent and fossil types have shown the practice to be 

 dangerous, and the discovery of D. Blakei plainly proves that hereafter we 

 must proceed most cautiously in the determination of species from the char- 

 acters of the radioles alone, no matter how strikingly they may appear to 

 differ. Certainly, if the present species had been dredged without its two or 

 three huge fan-shaped spines, it would have been unhesitatingly placed in the 

 genus Dorocidaris. and been perhaps referred even to D. papillata, although 

 there are differences in the coronal plates of the test and in the abactinal 



