NATURAL SCIENCES OF PHILADELPHIA. 



213 



DOSINIOPSIS. 



Equivalve, lentiform ; hinge with three cardinal teeth in each valve ; pos- 

 terior tooth of right valve bifid ; in the left valve a thick rugose lateral tooth 

 fitting into a cavity in the opposite valve ; under the apex is a pit or cavity ; 

 cartilage plate granulated ; pallial sinus deep and angular. 



Exteriorly the shells of this genus resemble Dosinia ; and the pit under the 

 apex and the form of the pallial impression are similar, but the anterior, 

 thick, rugose cardinal tooth, the posterior hinge channel and tooth-like plate, 

 and the muscular impressions ally it most nearly to Vtnilia and Cyprina. 



Venus lineolatus, Sowerby, has a hinge character nearly allied to, if not 

 identical with, this genus. 



D. meekii. Short ovate, ventricose, moderately thick, inequilateral ; ante- 

 rior margin regularly rounded ; posterior dorsal margin elongated, rounded, 

 very oblique, the extremity subangulated ; apex prominent ; basal margin 

 profoundly curved ; lunule obsolete, or defined by an obscure line ; surface 

 without other lines than those of growth. Height 1|- inch ; length If inch. 



Locality. Six miles east of Washington, D. C. Meek. 



Proportionally more elevated and convex than D. (Cytherea) lenticular is, 

 Rogers. 



A singular feature of this shell is a tuberculated callus under the anterior 

 cardinal plate, which occurring in 4 valves must be characteristic of the spe- 

 cies. It has the appearance of having grown up from the inner surface of the 

 valve and folded over the under side of the hinge plate. 



Mr. Meek found this species abundantly in a dark grey quartzose sand, six 

 miles east of Washington, D. C, in company with other new univalves and 

 bivalves. Cytherea lenticularis , Rogers, belongs to the genus Dosiniopsis, and 

 more closely resembles Dosinia exteriorly. Both characterize the oldest 

 portion of the American Eocene which has yet been observed. 



This genus, like the preceding, is remarkable for uniting the characters of 

 two families, Cyprinidie and Veneridse, which are obviously distinct in the re- 

 cent shells. 



1864.] 



Dosiniopsis Meekii. 



