'230 PALEONTOLOGY OF KENTUCKY. 



defined sulcus. Terminal margin of the rear wing concave, and the cardinal 

 extremity acute. 



The test is thick ; the left valve, in well preserved specimens, is covered by 

 numerous strong, simple, sharp, radiating striae, which are continuous from 

 the umbo to the margin ; intercalated radii are very seldom, but when they 

 exist they are finer than the balance. The radii are crossed by regular, 

 sharp, elevated, concentric lamellae, which, in well preserved specimens, are 

 produced into sub-tubular, spiniform extensions upon the rays. On the wings 

 the radii are less conspicuous, while the concentric lines of growth are there 

 more prominent and crowded. The specimen here described and figured meas- 

 ures in both height and length fifteen lines, and its hinge-line thirteen lines. 



Formation and Locality. Occurs in the Corniferous limestone of the Devonian formation at and 

 around the Falls of the Ohio. 



