201 



This species resembles in form Cyathocrinus robustus, 

 Troost, but is much more abruptly spreading and is not 

 contracted at the top of the first radial plates. The absence 

 of anal plates in Troost's species is a peculiar feature. From 

 Poteriocrinus pisiformis, Rcemer (Monograph of the Fauna of 

 Western Tennessee, pi. 4, fig. 7), it differs in the greater 

 expansion of the cup and in the form of the plates. 



Geological formation and locality. — In shales of the Niagara 

 group; Waldron, Indiana. 



GENUS ICHTHYOCRINUS (Conrad). 



ICHTHYOCRINUS SUBANGULARIS {Hall). 



Body narrowly turbinate, or obconic below the free arms, 

 angular above the base by the prominence of the radial 

 series; base truncate for the articulation of the rather 

 large column. Basal plates rudimentary, concealed by 

 the column. Subradial plates appearing pentangular from 

 their junction with the column, somewhat higher than 

 wide. The primary radial series consist of three plates 

 each, the first one pentangular with the upper angles 

 slightly truncated, the second quadrangular; the third 

 pentangular, supporting on its upper sides the first plates 

 of the second radial series. No interradial plates are seen 

 between the plates of the first radial series, above which 

 the structure is mostly unknown. 



Surface of radial plates elevated in the centre ; entirely 

 smooth. The centres of the radial plates at their upper 

 margins are depressed or emarginate, and their lower mar- 

 gins produced. 



The last mentioned character of this species corresponds 

 with the small patelloid plates of Forbesiocrinus, and in 

 most respects it resembles that genus except in the absence 

 of interradial plates. This species differs from any other 

 of the genus before described, in the narrowly turbinate 

 form of the cup and the subangular outline. 



Geological formation and locality. — In shales of the age of 

 the Niagara group ; Waldron, Indiana. 



