NATURAL SCIENCES OF PHILADELPHIA. 71 



more closely arranged, but above and behind this they become 

 more widely separated again, and nearly as oblique as the obscure 

 umbonal ridge, above which they are not defined. 



Length, 2.28 inches; height, 1 inch; convexity, about 0.85 inch 



This shell strongly reminds one, by its general outline and 

 physiognomy, of those Jurassic species for which Prof. Ao-assiz 

 proposed the genus Cercomya. In that group, however, tireVe is 

 no lunule, and I am not aware that any of the species of the same 

 are marked by radiating costaj as in the species under considera- 

 tion. From all that is known of its characters, I am inclined to 

 believe it more nearly allied to the curious Lyonsia-like Carbo- 

 niferous shells, upon which Prof McCoy originally proposed to 

 found the genus Sedgivickia, but which he afterwards referred to 

 the genus Leptodomus. Still, it differs from the group Sedgickkia 

 also, in the possession of radiating cost®. These are not mere 

 rows of granules, such as doubtless existed on nearly all the dif- 

 ferent types of this family {Anatinidse), but decided costc^, such 

 as we see in Fholadomya, and, what is rather singular, they do 

 not exist on the anterior part of the valves, but extend only as 

 far forward as the beaks, under which they end abruptly, the 

 anterior one being as strongly defined as any of the others,\vhile 

 only the concentric stria? and wrinkles exist on the anterior third 

 of the valves. In the possession of the radiating costte mentioned, 

 as well as in the shortness of its hinge and the inflection of its' 

 cardinal margin, and in its general physiognomy, it differs from 

 the typical species of AUorisma, and hence it may be thought 

 desirable to establish a subgenus for its reception, in which case 

 I would propose for the group the name Cer corny opsis. 



Along with the typical specimen of the foregoing species, another 

 was found, with the same form and surface characters, excepting 

 that the anterior end in front of the beaks is shorter, and more 

 angular at the lower end of the lunule ; while the anterior of its 

 radiating costs? are directed much more obliquely backward, in- 

 stead of descending vertically from the beaks to the base. This 

 specimen has tlie posterior end broken away, but as the peculiarities 

 mentioned seem not due to any distortion, I am much inclined to 

 believe it belongs to another species, for which AUorisma (Sedg- 

 wickia ?) obliqua would be a good name. 



Locality and position. Rushville, Ohio. Waverley group of 

 Lower Carboniferous. Prof Andrews' collection. 

 18TL] 



