CENTROSTEPHANUS CORONATUS. 40'J 



(DIADEMA.) Centrostephanus. 



Centrostephanus Pet., 1855, Denkseh. Akad. Berlin. 



Peters proposed to separate Diadema longispina of Philippi from the other 

 Diadematidae, on account of the globular outline of the test, and the presence 

 of ten large buccal plates ; subsequently I distinguished the genus Thricho- 

 diadema from the absence of a bare forking interambulacral space and the 

 peculiar structure of the abactinal system. This is nearly circular, the geni- 

 tal plates being pentagonal, and the anal system covered by comparatively 

 numerous, distinct plates unlike Diadema ; and still later, Verrill established 

 the genus Echinodiadema upon nearly the same grounds as Peters. An ex- 

 amination of original specimens satisfies me that the genus Centrostephanus 

 includes the genera of both Verrill and myself. The tubercles of both areas 

 are similar (as in Diadema and Astropyga), and arranged in two vertical rows 

 in the ambulacral zone. The buccal membrane is strengthened by ten large 

 plates, carrying spines as well as pedicellariae, — a feature not known in any 

 other genus of this family. The ocular plates are pushed out from the 

 genital plates by one small plate of the anal system, which separates the 

 genital plates. The stout spines resemble more the larger ones of Echino- 

 thrix, with closer verticillations, than those of Diadema ; they are still more 

 hollow, mere shells; actinal openings slight. The pores are arranged in 

 arcs of three, somewhat as in Astropyga and Diadema. Shell thick ; tuber- 

 cles crenulated and perforated. Teeth do not differ from those of the Diade- 

 matidae generally. 



Centrostephanus coronatus 



! Echinodiadema coronata Verrill, 18G7, Notes Radiata. 

 ! CenlTOSlephanus coronatus A. Ag., 1872, Rev. Eeh , Pt. I. 



Owing to great difference in size of C. coronata and C. Rodgersii, no com- 

 parison can be made of the rows of tubercles in the interambulacral spaces 

 in the two species. The actinal opening seems rather larger in proportion 

 (C. coronata), even after allowance for difference of size. The abactinal 

 region is also less depressed : but what will at once characterize this species 

 are, the striking differences noticed in the abactinal system ; the greater 

 size in C. coronata of the genital plates in proportion to the ocular plates, 

 their (genital) more elongate and pentagonal form, as well as a similar 



