Brachiopoda of the Cincinnati Group. 41 



gibbous part further back, near the umbo, from which point its surface 

 slopes off regularly to the front and lateral margins, without any dis- 

 tinct mesial elevation or depression ; beak moderately prominent or 

 projecting backward more or less beyond that of the other valve, and 

 somewhat arched but not properly incurved ; area two or three times 

 as high as that of the other valve, near the beak, and sloping off 

 rather rapidly to the lateral extremities, directed obliquely backward 

 and downward, and a little arched with the beak ; foramen usually 

 higher than wide. Interior showing hinge teeth to be prominent and 

 subtrigonal ; cavity for the reception of the muscular impressions 

 scarcely extending forward to the middle of the valve, tapering a 

 little toward the front, where it is more or less emarginate in the 

 middle, moderately well defined by a rather obscure, marginal ridge, 

 and divided within longitudinally by a low double ridge, that usually 

 extends forward beyond the muscular cavity, where it suddenly con- 

 tracts to a very narrow, obscure, single ridge, that again expands or 

 bifurcates farther forward ; scars of the divaricator and adjustor mus- 

 cles not very distinctly separated, and those of the adductors not 

 clearly seen in the specimens examined; ovarian areas compara- 

 tively rather large, and each occupied by a number of raised linear, 

 rather distant, and sometimes bifurcating ridges or lines, that radiate 

 forward and laterally. 



Surftice of both valves ornamented by distinct radiating strise, that 

 increase both by division and intercalation, and are crossed by much 

 smaller, regular, distinctly defined, imbricating, concentric marks, that 

 are more prominent between than upon the radiating strise, and pre- 

 sent a zigzag appearance, by being deflected backward on the stri« 

 and forward on the depression between them ; a few much shorter 

 imbricating marks of growth are also usually seen near the free mar- 

 gins of adult specimens. 



Length of a mature specimen, 0.60 inch; breadth, 0.78 inch; con- 

 vexity, 0.35 inch. 



Found about 100 feet below the Upper Silurian rocks, at Weisburg, 

 Clarksville, and other localities. At Weisburg, it seems to be confined 

 to strata about three feet in thickness. Good specimens are rare, but 

 valves are more abundant. 



Genus Hemipronites (Pander, 1830), as redefined by Prof. Meek. 



Shell varying from truncato-orbicular to semi-circular, or orbicular 

 subquadrate, more or less convex, the inequality of the valves varying 



