1887.] NATURAL SCIENCES OF PHILADELPHIA. 97 



among the Blastoids, they take the young stage of Alhigecrinus 

 (p. 72), as presenting "the simplest form of vault," i. e. five plates 

 without any central ; and Haplocrinus next, with a central piece and 

 five proximals, "neither AUagecrinus nor Haplocrinus having any 

 calyx interradials." Culieocrinus is cited as having five large summit 

 plates resting on the calyx interradials, and without any central 

 piece. Then come Plati/crinus and the Actinocrinidae as exhihiting 

 varying degrees of complexity, but having a central plate, which 

 they call an "oro-central," surrounded by proximals. In this case 

 also, they base a large part of their argument upon premises which 

 are by no means universally recognized, or are free from dispute. We 

 consider it far from being an established fact, that either AUagecrinus 

 or Haplocrinus Culieocrinus will be considered later on are 

 without calyx interradials. 



As we have before stated, Etheridge and CarjDenter maintain, and 

 it has been steadily insisted on by Dr. Carpenter since 1879, that 

 the proximal plates, surrounding the central plate in Palaeo- 

 crinoids, their so-called "orocentral," represent the five orals 

 of Neocrinoidea. This involves the assunijjtion of a homology 

 between a set of plates covering the actinal center, Avhich are five 

 in all stages of the Neocrinoids in which they exist, and a set of 

 plates which, when jjresent in Palaeocrinoids consist of six or 

 more plates, which do not cover the actinal center, but which 

 enclose another structui'e that does. It is in order to get rid of some 

 of these difficulties that the authors attach so great importance to 

 the cases of AUagecrinus, Haplocrinus, Culieocrinus, Coccocrinus, 

 and Stephanocrinus, in which they undertake to point out a series 

 of five plates at the ventral side, as the rej)resentatives of six or more 

 proximals in Palaeocrinoids generally, and which at the same time 

 might be successfully homologized with the orals of the Neocrinoids. 

 In this connection they remark on page 73 : 



"Since the preceding paragraph was in type, we have received 

 the latest publication of Messrs. Wachsmuth and Sj)ringer, 

 according to whom the five plates which form the ventral pyramid 

 of Stephanocrinus are 'calyx interradials,' and cannot therefore be 

 homologous with the orals of a Neocrinoid. In making this 

 comparison Messrs. Wachsmuth and Springer seem to have altogether 

 overlooked the fact that Stephanocrinus has well developed calyx 

 interradials, namely, the deltoids. ^ * * The American authors 

 regard the deltoid pieces of the Blastoidea, and by implication 



