1879.] NATURAL SCIENCES OP PHILADELPHIA. 329 



elevated above the line of the others, is less regular in form and 

 rests upon the truncated upper side of the basal and against 

 the two anal pieces, differing therein from Cyathocrinus, in which 

 basals and radials alternate all around. They consider the latter 

 a very important distinction between the two genera, but they 

 further assert that the best character for separation is to be found 

 in the presence of a single aperture in the dome of Poteriocrinus, 

 and of a separate oral and anal opening in Gyathocrinus. This 

 unfortunate and altogether incorrect statement on the part of de 

 Koninck has caused the utmost confusion, and when it was shown 

 by Meek & Worthen that the supposed oral aperture is closed in 

 perfect specimens in the one as well as in the other, some of the 

 leading authorities in Europe, who had previously expressed their 

 doubts as to the genus Cyathocrinus, wished to abandon it alto- 

 gether. We, for our part, cannot endorse this proposition, for we 

 think that the two genera are nicely defined by good generic char- 

 acters; and that has been the opinion of the American Paleon- 

 tologists generally, which has probabty arisen from the fact that 

 this country has produced far better specimens. 



But while American authors agree thus far, they differ in regard 

 to the proper limits of the genera. When in the course of recent 

 years a great variety of forms of Poteriocrinus were discovered , 

 Hall undertook to divide them subgenerieally, but in this he was 

 not very successful. In establishing his subgenus Scaphiocrinus T 

 he selected Scaphiocr. (?) simplex as type, a species which in its 

 anal arrangement and arm structure, though clearly distinct 

 from Poteriocrinus, agrees exactly with Graphiocrinus de Koninck 

 & Lehon. The majority of species, however, which were described 

 under Scaphiocrinus, agree substantially, both in the arms and 

 anal area, with Poteriocrinus, and we see no possibility of separat- 

 ing them. This may appear strange, for, on looking over a large 

 collection of Poteriocrinus, it seems to embrace a number of very 

 different groups; but an attempt to separate them will invariably 

 result in finding but few species agreeing in the same points. 



Hall defines Scaphiocrinus as follows: radials 2x5, botli pen- 

 tagonal, the first with the upper side straight or obliquely concave 

 the second with the lower side straight, often much elongated 

 and the plates contracted or concave on each side; anals four or 

 more; arms double from their origin, or rarely simple in the 

 anterior ray; arm plates simple, often wedge-shaped, with pinnulse 

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