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CRASSATELLA UNDULATA. Tab. 9, fig. I. 



Oblong subovate, much compressed, with coarse concentric 

 lines ; limbo flattened, and with regular concentric grooves; 

 apex subacute ; inner margin entire. 

 Syn. CKASSATELLA UJJDULATA, Say. Journ. A. N. S. v. 4, pi. xi, 



fig- 2. 



Localities. James River, near Smithfield, Va.; abundant; 

 York-town, Va. Upper Tertiary. 



Variety, A. Thick and ponderous ; not much compressed. 

 A specimen in the collection of the Academy is marked St. 

 Mary's county, Md. 



Young shells of this species closely resemble C. compressa 

 of Lamarck, as figured in Deshayes' Coq. Fos. des env. de Par. 



CRASSATELLA MELINA. Tab. 9, fig. 2. 



Ovate, thick, not compressed ; anterior margin obtusely 

 rounded ; posterior margin oblique and angular; dorsal margin 

 nearly straight ; concentric lines coarse ; umbonial slope suban- 

 gular and scarcely curved ; beaks with concentric grooves ; in- 

 ner margin entire. 



Locality. Cumberland Co. N. J. Upper Tertiary. 



This shell is intermediate to C. nndulata and Marylandica, 

 but is perfectly distinct from both. It occurs abundantly in 

 the tertiary marl, accompanied by Perna maxillata and several 

 new and interesting species. The existence of this formation 

 in New Jersey was first ascertained by means of some fossils 

 brought very lately from Stow creek, by Mr. Samuel Griscom, 

 who has since accompanied me to the spot. We traced it several 

 miles north of Stow creek, and in one instance found its surface 

 composed of a bed of the Ostrea virginiana or common oyster, 

 erroneously supposed to have been deposited by the Indians. 

 These beds occur in the same manner at Easton, Md. and 

 except in the Crag on the Potomac, always present fragments 

 of Pect'en madisonius, and other extinct species. There can 

 be little doubt that all those beds of oyster shells beneath the 



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