JEVom the Niagara Formation. 



67 



the interbrachial plate. The double second interradial plate, sur- 

 mounting the first interradial plate is distinctly concave, causing the 

 lobed character of the upper part of the calyx. The lower plates 

 of the arms, only, are preserved. 



Surface of the plates smooth or finely granulose. 



This species is conspicuously distinct from all others, in the con- 

 tracted lower part of the calyx and the abrupt expansion, giving 

 great gibbosity above, while it is contracted between the arms of 

 each ray by the concavity of the double interradial plates. 



Body turbinate, composed of the following series of plates : basal 

 plates three ; subradials five ; radials five in the first series, anal 

 area composed of several plates; arms unknown. 



This crinoid has the general form and aspect of Poteriocrinus or 

 Ctathocrixus, and has a similar structure above the basal series. 

 Three individuals have been examined, each one of which has the 

 remarkable protuberant attenuate base and large anal area. 



The accompanying diagram gives an illustration of the structure of the Genus. 



Body somewhat angularly turbinate, base a little protuberant for 

 the column attachment, narrow and distinctly pentangular above to 

 the middle of the subradial plates ; the areas formed by the lateral 



AMPHERISTOCRINUS nov. gen. 



Ampheristocrixus typxjs n. sp. 



