NATURAL SCIENCES OF PHILADELPHIA. 163 



anterior extremity. (Right valve unknown.) Length of left valve 

 0.55 inch ; height (behind the middle), 0.35; convexity, 0.10 inch. 



This is one of those peculiar forms presenting an intermediate 

 appearance between Avicula, Pterinea^ and Pteronites^ but not 

 agreeing exactly in outline with well-defined species of any of 

 these groups. So far as can be determined from casts of the left 

 valve only, it does not appear to have had the hinge teeth of 

 Avicula or Pterinea ; wiiile it also differs from the latter in not 

 having the posterior extremity of the hinge extended or acutely 

 angular, though there is an obtusely angular, slight posterior 

 dorsal alation, which, however, is not defined by any sinuosit^^ of 

 the posterior margin. From the forms on which the genus Ptero- 

 nites was founded, it differs in having the hinge a little shorter 

 than the posterior margin, and its beaks further removed from 

 the anterior extremity. 



There are probably several undefined genera among the Carboni- 

 ferous shells of this general appearance, that we have not yet the 

 means of defining. 



Locality and jyosifion. Newark, Ohio. "Waverley group of the 

 Lower Carboniferous series. 



CYPRICARDINA? CARBON ARIA, Meek. 



Shell small, longitudinally' oval, less than twice as long as high, 

 the widest (highest) part being under the posterior extremity of 

 the hinge ; rather gibbous, with often a shallow undefined impres- 

 sion or slight concavity extending from the beaks obliquel}^ back- 

 ward and downward to near the middle of the basal margin ; pos- 

 terior side rounded below the middle, and somewhat straightened 

 and sloping up obliquely forward to the posterior extremity of the 

 hinge ; anterior side extremely short and more or less rounded ; 

 cardinal margin nearl^^ straight or slightly arched, and about two- 

 thirds the length of the valves, sometimes showing a very faint 

 compression, or tendency to become a little alate behind; base most 

 prominent posteriorly, and gentl}' ascending forward, with a more 

 or less defined broad sinuosity along the middle ; beaks extremely 

 oblique, terminal, and so little prominent as scarcely to project 

 beyond the rounded outline of the anterior end. Surface orna- 

 mented by about twenty, very regularly disposed, subimbricating 

 lamina? of growth. 



o 



1871.J 



