250 Messrs. E. Etherlclge, Jun., ant? P. H. Carpenter on 



0. stelNformis, O. & S., sp., and 0. gracilis, M. & W. In 

 European rocks of corresponding age five species are now 

 known to occur. There are two British BUistoids referable to 

 this type, ahz. Pentremites injiatus, Phillips, and P. pentan- 

 gularis, Miller, sp., wliilst the other three are met with in 

 the Carboniferous Limestone of Belgium — Pentremites Puzos^ 

 Mlinster, P. Orhignyanus, de Koninck, and P. Waterhousianus^ 

 de Kon. The first two of these are somewhat aberrant forms, 

 presenting considerable difterences from the American species, 

 which approximate them to Plucnoschisma and Cadaster. 



The gap, however, is bridged over so completely by O. in- 

 flatus, Phillips, sp., and 0. Water Jwiisianus, de Kon., sp., that 

 we have no choice but to refer thera to this genus. 



Orojyhocriinis differs from Pentremites proper, Granatocriniis^ 

 Schizublastus, Pentremitidca, and probably also from Troosto- 

 crinus nnd TricceJocrinus, in the absence of marginal pores to 

 the ambulacra and of circumoral spiracles. The place of tliese 

 organs is taken by the ten elongated slits which run parallel 

 or subparallel to the ambulacra. Further, the anal aperture 

 of OrvpJiocrimis is sepai ate and distinct from these hydrospiral 

 openings, having no coimexion whatever with the latter, as is 

 the case with the fifth or complex s|)iracle of the genera men- 

 tioned above. Lastly, tlie orals, in consequence of the absence 

 of distinct spiracles^ are imperforate. Orophocrinus thus pos- 

 sesses only one series of openings leading to the hydrospires, 

 viz. the ten elongated slits bordering the ambulacra. The appa- 

 rent difference in number between the latter and the five spiracles 

 of a Pcnticmite is lessened when wc recollect that in the last- 

 named genus the spiracles are divided internally by a septum, 

 whilst in Schizohlastus they are separately developed and 

 correspond in number to the hydrospire- clefts of Orophocrinus. 



In the widening of these clefts in the Belgian species, O. 

 puzos, Miinster, sp., and 0. Orbignyanus, de Kon., sp., and 

 the partial exposure of the hydrospire-slits, we see a fore- 

 shadowing of the conditions met with in Pluv7ioscMsma and 

 Codaster. In both these genera there is likewise a separate 

 anal aperture, whilst the anal interradius bears hydrospire- 

 clefts in Phamcschisma and OrojjJwcrinus, but not in Codaster. 



A tendency towards the form of the true Pentremite is ex- 

 hibited by one species in particular, the O. gracilis, M. & W.*, 

 more than in any of the others. Although possessing the cha- 

 racteristic features of OropJiocriiivs, the upper portion of the 

 calyx is much higher and less depressed than in the typical 

 O. steUiformis. It also bridges over the gap between the 

 American and Euroj)can species ; for not only are the hydro- 



* Loc. at. V. t. 8. f. 6. 



