1887.] NATURAL SCIENCES OF PHILADELPHEA. 93 



figures only five plates of equal size ; and they add : " These five 

 plates of Stephanoerinus and Elaeacrinus have exactly the same re- 

 lation to the peristome and ambulacra as the oral plates of a Neocri- 

 noid, and we do not see how their mutual homology can well be dis- 

 puted." On page 74 they continue : "The difference between 

 Elaeacrinus elegans ov Stephanocrlnus and . Verneuili, as described 

 by Roemer, is very much the same as that between Oulicocrinus 

 and the simplest form of Platycrinus. Stephanocrinus, like Oulico- 

 crinus, has but five plates in the vault ; while in E. Verneuili there 

 are at least seven, viz. : one orocentral, four proximals of equal size, 

 and two smaller ones on the anal side." They allude to White's 

 description of the summit of Orophocrinus stelliformis as consisting 

 of five small plates etc., which they say is "'just as in Stephanocrinus 

 and in Elaeacrinus elegans" though they add that their arrange- 

 ment does not seem to be very constant. On page 75, they speak 

 of the summit of Granatocrinus Norwoodi varying in a similar man- 

 ner, and of a "somewhat less regular arrangement" in Schizoblastus 

 JSayi. 



It thus appears that their conclusion that the plates of the vault 

 in Blastoids "rarely exhibit any definite arrangement,"(p. 118) and 

 that there is a series of variations in the summit plates of the Blas- 

 toids similar to, and to some extent parallel with, those which they 

 assume to exist in l*alaeocrinoids, is based on the presence of five 

 plates in Stephanocrinus ; the assumption of five plates in Elaeacrinus 

 elegans and Oro])hocrinus stelliformis, in contrast with seven plates 

 in E. Verneuili; and variability in the number and arrangement 

 of plates in the summit of Granatocriyius Norwoodi and Schizoblastus 

 Sayi. 



It is somewhat unfortunate for the validity of this speculation 

 that Stephanocrinus cuts so important a figure in it, as it has since 

 been discovered to be not a Blastoid at all, but a brachiate Crinoid ; 

 a fact,^ it is proper to say, which is noticed by the authors in 

 their preface. This genus, therefore, must be eliminated from among 

 the premises on which the argument is built, and the "simplest 

 form" must be looked for elsewhere. Let us see how far the others 

 will stand the test of examination. 



Elaeacrinus elegans was described by Hall - under Nucleocrinus, 

 and in his specific description, and not simply in his generic diag- 



1 Revision of the Palaeocrinoidea, Pt. Ill, p. 282, etc. 

 M5tli, Rep. N. Y. St. Cab. Nat. Ilist. 1862 .p. 147. 



