

the Morphology of the Blastoidea. 233 



distinct anus and of ten spiracles 5 but these openings are close 



to the peristome in the latter genus, and bounded by the orals, 



while the external aspects of the two types are entirely 

 different. 



The same may be said of Orophocrinits, which likewise has 

 a distinct anus and ten groups of hydrospires. The enlarged 

 proximal ends of the clefts by which these open externally 

 represent the spiracles of Acentrotremites ; and in the best- 

 known species, 0. stelliformis, they occupy very much the 

 same position as their homologues do in that genus, viz. at 

 the junction of the oro-radial sutures with the ambulacra. 

 But the other characters of Oropkocrinus 7 and more especially 

 those of the European species, are such as to separate it en- 

 tirely from Acentrotremites. 



Eleacrinns is yet another type with ten spiracles and a 

 separate anus. But the asymmetry of its calyx and the im- 

 mense size of its oral plates, which alone form the spiracles, 

 separate it distinctly from Acentrotremites. We think, how- 

 ever, that these two genera, together with Sclnzoblastus, form 

 a tolerably well-defined family, which we propose to call 

 Eleacrinidse. Its leading characters would be, trie generally 

 ^ elliptical form of calyx, the presence of ten groups of hydro- 



spires, and in most cases of a corresponding number of 

 spiracles, which merely notch the sides of the oral plates, 

 and the independence of the anal opening from the spiracles 

 except in certain species of Schizoblastus. 



The national collection at South Kensington contains two 

 specimens of Acentrotremites , which have enabled us to study 

 some of the characters of this peculiar type. One of them is 

 from the Carboniferous rocks of Somersetshire, and corre- 

 sponds in its general appearance with the Mitra elliptica of 

 Cumberland*. The other, collected in Derbyshire by the late 

 Mr. Eofe, is merely a fragment, showing portions of three 

 ambulacra ; but it is obviously congeneric with the Somerset- 

 shire species. The latter is of unusually large size, being 

 30 millim. high and 25 millim. across the base, and must be 



considered the type of the genus. It has very much the 

 general form of Granatocrinus derbiensis or of if. campanu- 

 la tus, while the Clitheroe species must be more like G. ellip- 

 ticus or G. elongatus. There is a curious point of difference 

 between the Somersetshire example and Cumberland's figure 

 of Mitra elliptica. The latter shows five basal plates, occu- 

 pying the larger portion of the flattened base of the calyx; 



Reliquiae Conserratffi (Bristol, 1826), p. 33, pi. B. 





