Brachiopoda of the Cincinnati Group. 33 



Length varies from one eighth to half an inch, though usually about 

 one-fourth of an inch. 



It is found at the quarries surrounding Cincinnati, at an elevation 

 of 340 to 400 feet. It is found at Hamilton, Butler county, at a cor- 

 responding elevation. It is not a common fossil. 



For Orihis (?) morrowensis (James) see vol. 1, p. 21, of this Journal, 

 January, 1874. 



Orthis costata — (Hall, 1845). 



Semi-circular or semi-oval ; surface marked by about twelve strong 

 ribs ; area well defined, proportionally large ; hinge line scarcely equal 

 to the width of the shell, which is about one fifteenth of an inch. 



This is a very minute fossil, and known to me only from the top of 

 the hill at Mount Auburn, in Cincinnati, at an elevation of about 400 

 feet above low water-mark. It is possible that it is the young of 0, 

 plicatella. 



OhMs James i — (Hall). 



Shell transversely semi-elliptical ; hinge line equaling, or a little 

 greater than the width of the shell below ; the length a little more than 

 half the wadth, and sometimes nearly two thirds. Cardinal extremi- 

 ties compressed, and usually truncate or rounded. Dorsal valve con- 

 vex, becoming gibbous, with a shallow, often scarcely defined sinuosity 

 in the middle ; hinge line slightly rising toward the beak, which is not 

 incurved ; area narrow, but distinctly defined ; foramen broad, and 

 showing a narrow process, which rises as high as the plane of the area. 

 Ventral valve much elevated toward the beak ; the sides somewhat 

 flattened, and the middle sometimes a little depressed toward the front; 

 the beak slightly arcuate, and the wide area nearly flat and moderately 

 inclined backward ; foramen large, and extending to the apex. 



Surface marked by twenty to twenty-four simple, strongly rounded, 

 slightly arching, primary strife, which, by intercalations of secondary 

 striae, are often increased to twice that number on the margin. 



Often the striae are simple throughout, and, when well preserved, 

 ai-e always marked by fine, thread-like, concentric strise, and toward the 

 margin a few lamellae of growth. 



This species, in general form, resembles O. plicatella, but the area 

 is much larger, and extends to the salient cardinal extremities ; while 

 in that species the extremities are usually rounded, and the shell is a 

 little rounded below. 



Found at Cincinnati, at an elevation of about 400 feet. 



