18SG.] NATURAL SCIENCES OF PUILADELPUIA. 213 



orals, and also the honiolognes of the six or more proximals of the 

 Platycrinidie and Actinocrinidse, and of the five summit plates in 

 Stephanocrinus, which all cover the peristomial area but not also 

 the tentacular vestibule and the disk, it would follow that in the 

 three latter the orals were carried inward by the cah- x interradials 

 b}' which they are surrounded, but not only, as perhaps might be 

 the case in the Camarata, by their higher orders or upward growth, 

 but even by the primary interradials. It would further suggest 

 that in the earliest genera Beteocrinus, Glyptocrinus and allied 

 forms, which have no proximals, the " orals " were unrepresented 

 or resorbed. Also Nanocrinus paradoxus (Echin. Eifl. Kalk., 

 PI. 12, fig. 7 i) has no proximals, the covering pieces, according 

 to our interpretation, rest directly against the central plate. 

 This, we know, is tlie case in two undescribed species of Talaro- 

 crinus, which we discovered lately in Kentucky. In these species 

 the central piece is relatively larger than the combined orals of 

 Stephanocrinus, there are no proximals, and no other interradial 

 plates touching the central plate. The covering pieces occup}^ 

 here a similar position to the central plate the coalesced orals 

 as in Stephanocrinus to the quinque partite oral pyramid. There 

 we have actual specimens, which in all essential points conform 

 with the hypothetical Crinoid which we constructed. 



From Carpenter's arguments (Chall. Rep., pp. 268-2T1) we 

 conclude tliat he regards the hypothetical "orocentral" a kind 

 of keystone, by which the actinal system is closed in a similar 

 manner as at the opposite pole the dorsocentral is said to close 

 the abactinal side. Unfortunately, however, this theory as stated, 

 is not sustained by embryology. No such plate has ever been 

 discovered among living Crinoids, not even in their larval state, 

 before the opening of the tentacular vestibule, which is said 

 to represent the condition of Haplocrinus morphologically. 

 This difficulty Carpenter undertook to explain on p. 270 b}' stating, 

 that if such a plate appeared " it would only be in the way, and 

 have to undergo resorption to a greater or less extent." A weak 

 argument considering that orals of recent Crinoids actually 

 undergo that resorption. But, admitting it, what then became of 

 the orocentral of Stephanocrinus^ AUagecrinus and Coccocrinus, 

 and what of the central piece in the oral pj'ramid of certain Cys- 

 tidea ? He states further " the former (basals) are within the 



