COAL-MEASUEE SPECIES. 343 



ridges not quite so prominent, while I have seen no indications of the 

 minute sculpturing of that species. 



In regard to the hinge of the typical species of Cypricardina nothing 

 is known. In the shell here described, however, one of the casts shows 

 that it has a moderately well-developed hinge plate, with one linear 

 tooth in one valve, and one or two in the other, running very nearly 

 parallel to the cardinal margin along its entire length, and at the pos- 

 terior end of the hinge one or two shorter linear teeth, parallel to and 

 beneath the others, while at the anterior end there is, in the right valve, 

 one very small, slightly oval tooth, fitting between two similar ones in 

 the left valve. These little teeth are slightly compressed from above 

 and below, and placed so as to range, with their longer axis, nearly par- 

 allel 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 for an internal 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 Cypricardina 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 probably belongs to a 

 distinct Carboniferous group, nearly allied to the Silur.an genus Cypri- 

 cardites of Conrad, but differing in having its principal liinge teeth 

 extending the entire length of the cardinal margin, with cardinal area 

 nearly or quite obsolete, and anterior muscular impression very obscure. 

 It also diff'ers from the known species of Mr. Conrad's genus in having 

 remarkably regular, prominent, imbricating, concentric ridges or laminae. 

 Area squamosa, A. obscura, and A. faba, DeKoninck, belong apparently to 

 this group, and possibly also the form he has referred, in his work on 

 the Carboniferous fossils of Belgium, to A. cucullas obtusa of Phillips, 

 though the latter approaches still more nearly the typical Silurian forms 

 of Cypricardites in its hinge characters. • 



If Cypricardina shall be found to have a different hinge structure, I 

 would propose for the group, including our shell, the name Synopleura, 

 in allusion to its regular, concentric lamina or costse of growth. It is 

 possible, however, that this group may be thought too nearly allied to 

 Cypricardites to stand as a full genus, in which case the name of our spe- 

 cies would have to be written Cypricardites {Synopleura) oarbonaria-. 



Locality and position : Newark, Ohio. Lower Coal Measures. 



