CROTALOCRINUS CORA (HALL). 



Among the internal casts of crinoids which occur commonly 

 in the dolomitic Niagaran limestone of northeastern Illinois and 

 southeastern Wisconsin, is a species which was first described by 

 Hall in 1868 under the name Cyathocrinus cora. The cotypes of 

 this species, two in number, are recorded from Racine, Wis., and 

 are now preserved in the collections of the American Museum of 

 Natural History in New York. Specimens very much larger 

 than these types frequently occur in the dolomite near Chicago, 

 but they resemble them in all essential characters and all are 

 undoubtedly specifically identical. 



The body of this crinoid is more or less subglobular in form, 

 with a large column, and has been but rarely found preserved in 

 any condition other than as internal casts. The plates compos- 

 ing the body are arranged essentially as in members of the 

 genus Cyathocrinus. There are five large underbasals which 

 support five large basals, four of which are hexagonal in outline, 

 the fifth being heptagonal by reason of the truncation of the 

 distal angle for the support of a single subquadrangular anal 

 plate. The radials are large, wider than high, and are in con- 

 tact laterally, except the two posterior ones, which are separated 

 by the large anal plate. Until the discovery of the specimen 

 illustrated in the present paper, the plates above the radials 

 have never been observed, or at least they have never been 

 recognized as belonging to this species. 



In 1900 a single imperfect radial plate of a crinoid, with 

 brachial plates attached, was recognized by Weller as represent- 

 ing the genus Crotalocrinus, and was described under the name 

 C. ameiicaniis. This specimen is a natural mold of the exterior, 

 and was found associated with Cyathocrinus cora, but there was no 

 evidence by which the two forms could be correlated. 



There has recently come into the possession of the Walker 



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