October, 1843.] 305 



By permission of the Society, the Committee to whom was 

 referred Mr. Conrad's paper, read at the meeting of 19th 

 September, presented a report in favour of its publica- 

 tion. 



Descriptions of a New Genus, and of twenty-nine new 3Eocene, and one 

 Eocene Fossil Shells of the United States. 

 By T. A. Conrad. 



Carditamera. 



C. carinata. Trapezoidal, slightly contracted from beak to base ; ribs about 

 18, profound, flattened on the back, square, carinated on the posterior margin ; 

 posterior ribs rounded and the carina obscure or wanting; middle and anterior 

 ribs about as wide as the interstices ; all the costse with transverse coarse pro- 

 found wrinkled lines. 



Locality. Newbern, N. C. 



Compared with C. arata, this species differs, in being less ventricose over the 

 umbonial slope, in having a carina on the ribs, more distant transverse strise, the 

 beaks further from the anterior margin, and the posterior side narrower, with a 

 more oblique posterior margin. 



C. protracta. Trapezoidal, elongated, compressed, widely contracted from 

 beak to base ; dorsal and basal margins nearly parallel ; ribs about 15, the middle 

 ones triangular and crenated ; posterior ribs rounded and having distant arched 

 squamose coarse strise ; summit of the beaks scarcely prominent above the 

 hinge line. 



Locality. Patuxent River, St. Mary's Co., Md. 



Arca. 



A. triquetra. Subtriangular, profoundly ventricose ; umbo very broad and 

 prominent, beaks remote, profoundly incurved ; disk flattened posteriorly ; ribs 

 about 30, narrow, not very prominent, square; surface of the valves with coarse 

 crowded concentric imbricated lines; umbonial slope forming a right angle 

 with the posterior slope ; cardinal area dilated ; cardinal plate narrow, the teeth 

 small. 



Locality. Cliffs of Calvert, Maryland. 



This species differs from A. callipleura in having narrower ribs which are neither 

 crenated nor longitudinally striated as in that species. The A. callipleura is not 

 flattened posteriorly on the disk, and the umbonial slope is slightly arched in 

 the middle, while in the triquetra it is somewhat concave. 



Nucuia. 



N. liciata. Ovate-acute, ventricose, with about 15 concentric lamelliform 

 strise ; posterior side much shorter than the anterior ; anterior side slightly re- 

 curved, with an oblique slight submarginal furrow, causing a slight emargination 

 of the base near the extremity. 



Locality. Cliffs of Calvert, Md. 



