Maryland Geological Survey 565 



Description. — " E. costata, apex lateral, with about two volutions; 

 inferior valve convex, costate, transversely corrugated, costae of the disk 

 somewhat diehotomous, sometimes fornicated; within, a single profound 

 cicatrix placed rather nearer to the inner side; hinge with two nearly 

 parallel, profoundly excavated grooves, of which the inner one is shorter, 

 and corrugated ; superior valve flat, slightly concave, destitute of costae, 

 outer half exhibiting the increments, outer edge abruptly reflected from 

 the inferior surface to the superior, but not elevated above it; hinge with 

 a single groove on the edge ; cicatrix profound. Length four inches, 

 breadth three and a half. | Cabinet of the Academy of Natural Sciences. 

 — Peale's Museum. | This interesting shell is the largest and most perfect 

 of its class which has yet been found in the Ancient Alluvial deposit of 

 New Jersey. It is not uncommon. 1 have seen may specimens. They 

 vary somewhat in the costas, being sometimes almost antiquated, some- 

 times nearly smooth. The aged shells became extremely thick and pon- 

 derous." — Say, 1820. 



The representatives of the species occurring in the middle Atlantic 

 States are much less strongly costate than those of the Gulf. In the 

 majority of adults found in Maryland the radial sculpture does not persist 

 beyond the dorsal half of the shell, and even within that restricted area it 

 does not heavily corrugate the shell as in the typical southern E. costata. 

 Indeed, the differences are so obvious and so constant that a subspecific 

 separation would not seem amiss, lint in that case, the New Jersey and 

 Maryland race must be regarded as typical. 



Stoliczka has reported the fonn from the Ootatoor group of southern 

 India supposed by him to be correlated with the Cenomanian and lower 

 Planer of Europe. Judging from the figures, however, the Indian form is 

 less convex and ponderous than the American, with a more regular outline 

 and a less regular sculpture. It would be interesting, indeed, if this 

 highly specialized form should occur in India, since it is not known either 

 from the western United States or from the European continent. 



Occurrence. — Matawan Formation. Post 357 and Post 133, Chesa- 

 peake and Delaware Canal, Delaware. Monmouth Formation. Two 

 miles west of Delaware City, on John Higgins farm. Post 156, Briar 



