164 PROCEEDINGS OF THE ACADEMY OF 



licngtb, 0.56 inch; height, 0.34 inch; convexity, about O.lt 

 inch. 



This little shell agrees very nearly, in size, form, and ornamen- 

 tation, with the t3^pical forms of the group for which the name 

 Cypricardina was proposed, excepting perhaps the fine sculptur- 

 ing seen between the larger regularly disposed lamina of growth 

 in those shells, though even these markings may possibly exist on 

 well-preserved specimens of our species. 



In regard to the hinge of the t3'pical species of Cypricardina, 

 nothing is known. In the shell here described, however, one of 

 the casts shows a moderately well developed hinge plate, with 

 one linear tooth in one valve, and two in the other, running nearly 

 parallel with the cardinal margin along its entire length, and at 

 the posterior end of the hinge one or two shorter linear teeth 

 parallel to and beneath the others ; while at the anterior end of 

 the hinge, in the right valve, there is one very small, slightly 

 oval tooth, fitting between two similar minute teeth in the left 

 valve. These little teeth are slightly compressed from above and 

 below, and range with their longer diameter nearly parallel to the 

 hinge margin. No cardinal area can be seen, though there may 

 have been a very small narrow one immediately between the 

 beaks, as there is no cavity seen in the hinge margin for an inter- 

 nal cartilage. The muscular and pallial impressions are so faintly 

 marked that no traces of them have been seen on the casts of 

 the interior. 



Until the hinge of the typical species of CypiHcardina can be 

 made out, it is impossible to determine whether our shell belongs 

 to that genus or not. I have the impression, however, that it 

 belongs to a distinct Carboniferous group nearly allied to the 

 Silurian genus Cyp)ricadites of Conrad, but differing in having 

 its principal hinge teeth extending the entire length of the car- 

 dinal margin, with the cai'dinal area more or less nearly obsolete, 

 and the anterior muscular impression very obscure. It also dif- 

 fers from the known species of Mr. Conrad's genus, in having 

 remarkably regular, prominent, imbricating, concentric ridges or 

 laminffi. Area squamosa, A. obscura, and A. faba, de Koninck, 

 belong apparently to the same group, and possibly also the form 

 referred by this same author to A. obtusa, Phillips, though the 

 latter approaches still more nearly to the tj'pical Silurian forms 

 of Cypricardites in its hinge characters. 



[August 15, 



