FOSSILS OF THE NIAGARA GROUP. 371 



radials small, elongate, hexagonal ; third radials smaller than the 

 second, wider than high, and variable in form, being mostly hepta- 

 gonal, supporting on their upper sloping faces supraradials, the 

 number and extent of which are unknown. First interradial plates 

 large, hexagonal, succeeded by two vertical ranges of smaller poly- 

 gonal plates. Anal area unknown. 



The specimen from which the above description is taken is an internal 

 cast, imperfect on one side, so that the entire characters are not seen ; 

 but the large size of the first radial plates, and the constriction of the 

 sides above the middle of these plates, is very remarkable. From the 

 characters on the cast it would appear that the plates were marked by 

 rather strong radiating ridges, which rising from a point above the centres 

 of the first radials, pass to the interradial plates above, while the first 

 radials are smooth below, and in their upper part are marked by sharp 

 roimded ridges, rising from the same point as the oblique ridges, extend- 

 ing upwards and bifurcating with the divisions of the ray as far as pre- 

 served in the specimen. 



This feature of narrow rounded ridges, following the divisions of the 

 rays, is approached in some specimens of Saccocrinus christyi = A. (S.) whit- 

 fieldi ; but the oblique ridges have not been observed, while the entire 

 calyx is much less expanded than in that species. 



Formation and Locality. — In limestones of the age of the Niagara 

 group, at Racine, Wisconsin. 



GENUS MACROSTYLOCRINUS,* Hall. 



CYTOCRINUS,t RoEMEE. 



Macrosttlocrinus striatus, Hall. 



PLATE X, FIGS. 7, 8. 



Macrostylocrinus striatus. Hall; in Transactions Albany Institute, IV, p. 207. 1862. 



The originals of this species are from Waldron, Indiana. A cast of a 

 species of this genus from Racine is similar in form and proportions, and 

 is probably identical with those fi-om Waldron. 



* Palaontology of New York, Vol. ii. 1852. 



I Silurische Fauna des Westlichen Tennessee. 1860. 



