CROTALOCRINUS CORA {HALL) 533 



Museum, through the generosity of Mr. G. F. Harris, of Chicago, 

 a specimen of the so-called CyatJwcrinus cora, upon which nearly- 

 all of the plates of the calyx are preserved, as well as some of 

 the brachial plates. This specimen demonstrates that the type 

 of Crotalocrinus americanus is nothing more than a radial plate 

 with brachials attached of the so-called Cyathocrinus cora, and 

 that the latter species must be transferred from the genus 

 Cyathocrinus into Crotalocrinus. This remarkable genus of 

 crinoids, therefore, which has hitherto been considered as such a 

 rarity in the Niagaran fauna of America, proves to be one of the 

 common members of the fauna of this age in Illinois and Wis- 

 consin. It is of especial interest because it is one of those 

 peculiar forms which relates the Niagaran faunas of the interior 

 of North America, so closely with the faunas of Gotland and 

 England. 



This American species of Crotalocrinus is most closely allied 

 to C. riigosus Miller, var., from Gotland, as illustrated by 

 Angelin. 1 Both have the same subglobular form of calyx, con- 

 stricted at the top of the radial plates, and both have the same 

 style of surface markings, consisting of shallow furrows which 

 cross the sutures dividing the plates at right angles. In the 

 American specimens these markings are so pronounced as to be 

 usually discernable even on internal casts. The arrangement of 

 the fixed brachial plates in the two species, however, is quite 

 different, if Angelin's illustrations can be depended upon. 



In the arm plates of Crotalocrinus the axial canals are a con- 

 spicuous feature. In converging toward the base of the arm, 

 these canals unite into a single trunk which pierces the radial 

 plate. The axial canals are well shown in both the specimens 

 preserving the brachial plates, and the casts of the canals are 

 frequently more or less well preserved in the internal casts of 

 the species as it is ordinarily preserved. 



The species which has been described as Cyathocritius va?i- 

 hornei S. A. M. is probably another member of the genus Crotalo- 

 crinus. It is known only from internal casts, but these speci- 



^Iconog, Crin., Plate 17, Figs. 8, 8a. 



