34 Brachiopoda of the Cincinnati Group. 



Orthis clytie — (Hall) . 



Shell larger than medium size, semi-elliptical, the length about as 4 

 to 5, or as 7 to 9, plano-convex or concavo-convex ; hinge line less 

 than the greatest width of the shell ; cardinal extremities rounded. 

 Dorsal valve flat or concave, with a longitudinal depression along the 

 center ; cardinal area linear, not incurved ; ventral valve moderately 

 convex ; sometimes more elevated or subangular along the middle, 

 toward the beak ; area narrow, longitudinally striated, and extending 

 a little more than two thirds of the shell ; foramen wide ; beak scarcely 

 incurved. Muscular impression deeply divided ; in the middle of the 

 inner division of each lobe, more deeply impressed, and extending two 

 thirds of the length of the shell from the beak ; the outer portions 

 flabellate, and margined by an elevated ridge ; the whole interior sur- 

 face granulose, and the visceral area margined by a thickened eleva- 

 tion, which becomes, in old shells, a defined ridge. The striae are 

 shown along the inner margin. 



In the dorsal valve the inner surface is finely striato-granulose, and 

 outside of the submarginal ridge the striae are stronger. The muscu- 

 lar impression is comparatively small, distinctly circumscribed, with 

 central ridge thin, prominent cardinal process, and strongly defined 

 dental fossets and corresponding crural processes. 



The surface is finely and somewhat evenly striated ; the striae on the 

 ventral valve often more prominent than those on the dorsal valve. 



This is a very well marked and distinct species, which in the deeply 

 bifid muscular impression differs from any other species in this group 

 of strata ; while in other features it is readily distinguished. 



Found at Paris, Kentucky. 



OHMs occidentalis — (Hall, 1847), 



Shell attaining a moderately large size, wider than long, varying 

 from transversely subquadrate to semi-oval, becoming quite gibbous 

 with age ; hinge line exceeding, about equaling, or sometimes a little 

 less than the breadth of the valve at any part farther forward, lateral 

 extremities moderately compressed, varying from rather acutely to 

 more or less obtusely angular ; lateral margins often a little 

 sinuous behind, but sometimes straight or convex in outline, but 

 rounding to the front, which is nearly always a little sinuous, and 

 sometimes rather decidedly so in the middle. 



Dorsal valve more convex than the other, especially in the large 



