76 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Pygmjeocidaris. 



Doderlein, 1905. Zool. Anz., XXVIII, p. 622. 



Type-species, Podocidaris prionigera A. Agassiz, 1879. Proc. Am. Acad., XIV, p. 199; 

 1881, "Challenger" Echini, p. 59; PI. XXXIV, figs. 14, 15. 



This is still another monotypic genus, the characters of which have been 

 well discussed by Doderlein (1906), who points out some remarkable sim- 

 ilarities between it and the notable genus Tiarechinus. It has so far been 

 found only in the East Indian region, at depths of 372-1534 fathoms. It 

 seems clear to us that the specimens collected by the "Sibofja" and c.illed 

 by de Meijere " Podocidaris spec." are not only not prionigera, as Doder- 

 lein lists them, but are not even congeneric with it. 



^ Habrocidaris. 



A. Agassiz and Clark, 1907. Bull. M. C. Z., L, p. 234. 

 Type-species, Podocidaris seutata, A. Agassiz, 1880. Bull. M. C. Z., VIII, p. 72. 



This genus, established for Podocidaris seutata A. Ag., from the West 

 Indies, also includes the closely allied species, Z?. ar^eniea, from the Hawaiian 

 Islands. It is evident fi'om the peculiar structure of the actinal inter- 

 ambulacral system of Podocidaris and its allies that we are justified in sep- 

 arating P. scidata A. Ag. from Podoeidaris scidpta A. Ag., and that we must 

 agree with Doderlein also in separating the remarkable Podoeidaris prionigera 

 A. Ag. as a distinct genus, allied to Tiarechinus, under the name of 

 Pygniteocidaris. 



Habrocidaris A.Ag. and CI. is more closely allied to Pygmaeocidaris Dud. 

 than to Podocidaris as now limited, which in the arrangement of its inter- 

 ambulacral tubercles retains more its Arbacia-like characters than do these 

 other genera. 



Characteristic of Habrocidaris is the very thin, delicate test, fhe slightly 

 indented peristome, the close plating of the actinal system, and the distinctly 

 triangular primary radioles. 



While studying the permanence of the odd actinal interambulacral 

 primordial plate among the regular Echini, one of us, as far back as 1883, 

 was struck with the possible affinity of the Arjjaciadae to Tiarechinus Neumayr, 



> "Blake " Echini, Mem. M. C. Z., X, No. 1, p. 22. 



