30 Brackiopoda of tJie Cincinnati Group. 



Surface of both valves ornaraented by distinct, rather prominent, 

 radiating ribs, about forty of which may be counted on each valve of 

 a medium-sized specimen ; the furrows between the ribs equaling the 

 breadth of the ribs themselves ; larger individuals sjometimes having a 

 few of the ribs bifurcating once, and an occasional smaller one inter- 

 calated between two of the larger, so as to increase the whole number 

 at the free margins to about fifty. Concentric strise nearly or quite 

 obsolete ; but in old specimens, one or more sub-imbricating mai"ks of 

 growth may sometimes be seen near the free margins. 



Breadth of a large specimen, 0.74 inch ; length, 0.64 inch ; convexity, 

 0.33 inch. 



Found at Frankfort, Kentucky, and at other places in the lower part 

 of the Cincinnati Group ; but rare. 



Orthis plicateUa — (Hall, 1847). 



Broadly semi-oval, nearly equivalve, length and breath about as 3 

 to 4 ; surface marked by simple, strong, angular, radiating plications, 

 about 20 to 28 on each valve, crossed by simple, elevated, concentric 

 lines, which are more distinct in the depressions between the costae, 

 and often obscure or obsolete upon their exposed surfaces ; valves 

 nearly equally convex, Avithout sensible depression or elevation on 

 either one, meeting at the edges in a straight line ; cardinal line not 

 extending beyond the width of the shell ; area narrow ; dorsal foramen 

 extending to the beak. 



It is found at Cincinnati, from about 300 feet above low water-mark, 

 to the top of the hills. Its range, so far as known, is from 300 to 500 

 feet above low water-mark, and it is not rare where the rocks of this 

 horizon are well exposed. It is usually found where the 0. fissicosta 

 abound. 



Orthis fissicosta — •( Hall, 1 847) . 



Serai-oval, with the cardinal line somewhat less than the width of 

 the shell ; area narrow ; foramen narrow, triangular, reaching to the 

 apex ; dorsal valve moderately convex, with the beak extending and 

 slightly incurved ; ventral valve moderately convex in the middle 

 and depressed at the sides ; surface marked by angular costae, which 

 become bifid and trifid on the center or toward the margin of the shell ; 

 number of costae about 19 or 20. 



Found at Cincinnati, from 300 to 400 feet above low water-mark, and 



