PHOLIDOPS. 81 



Genus Piiolidops ( Hall). 



All the known species of this genus are small shells, usually occurring 

 as single scale-like valves or discs, and in two instances only have I seen 

 specimens with the valves conjoined. The specimens appear not unlike 

 the dorsal valves of a small species of Discina ; but being calcareous, they 

 have not the corneous lustre of those shells ; and when conjoined, there 

 is no evidence of a foramen in either valve. The interior shows a strong 

 muscular callosity, and the casts bear a strongly marked impression of 

 the same. 



Piiolidops areolata ( n. s.). 



PLATE III. 



Shell broadly subovate or scarcely circular, wider on the posterior third, 



broadly rounded behind and more narrowly rounded in fi'ont. 



The cast of one valve ( the dorsal valve ? ) shows a deep ovate or sub- 

 cordiform muscular scar, which is nearly surrounded by an elevated 

 areola, and partially divided by a median ridge from above. The opposite 

 (ventral?) valve has a larger muscular scar, which is auriculate above, 

 with the surrounding areola divided at the lower or anterior margin. 

 Surface somewhat abruptly flattened on the posterior side, and more 

 gently sloping on the front of the valve. 



One specimen has a length a little less than one-fourth of an inch, with 

 a width across the middle nearly the same. The only specimens known in 

 the Schoharie grit are casts, and we have not therefore seen the exterior 

 of the shell. In casts of two individuals, the muscular impressions present 

 some differences in form, and in the depth of the impressions of the 

 parts, probably indicating the characters of dorsal and ventral valves. 



This species closely resembles one in the Oriskany sandstone, from which it 



