T. C. Brown — Fauna from Chwppaqui-ddick Island. 233 



Corbula Whitfieldi sp. n. PI. VIII, fig. 3. 



Shell large for the genus, ventricose and snbtriangnlar ; beak 

 high and incurved ; anterior margin sharply rounded, ventral 

 margin broadly arcuate in the median and anterior portions 

 but sinuously e margin ate posteriorly ; the posterior end of the 

 shell is narrow, produced and abruptly truncated. Surface 

 marked by distinct concentric asymmetrical folds or concentric 

 wrinkles which are broadly rounded on top, with the dorsal 

 border slightly broader and not as abruptly sloping as the 

 ventral border. The folds are separated by narrow channeled 

 interspaces. These folds constitute a surface ornamentation, 

 and not lines of growth, as is shown by the fact that they 

 increase in number by intercalation, some folds extending from 

 the anterior to the median portion of the shell, while others 

 extend almost to the posterior end. The principal folds extend 

 to the posterior end and are there sharply Hexed. These folds 

 are well defined on the ventral half of the shell and become 

 finer and more crowded on the umbones and almost disappear 

 at the beaks. 



This species approaches very closely in general outline and 

 surface ornamentation to C. alaeformis* Gabb, from the 

 Tejon formation of California, but is less than one-half as 

 large. The concentric folds become finer and more crowded 

 on the umbonal region in the specimen from Chappaquiddick 

 than in that figured by Gabb. 



This species also somewhat resembles C. subenqonata\ Dall, 

 from the Eocene of Maryland and Virginia, but differs from 

 that species in being narrower anteriorly and more produced 

 posteriorly, and in the absence of a subcarinate ridge extending 

 from the umbo to the posterior margin. The concentric folds 

 are also more crowded and less prominent on the umbonal 

 region. 



The material in hand represents a right and a left valve. 

 These specimens occur in a very fine-grained hard ferruginous 

 lutyte concretion, quite different in character from the material 

 in which most of the other fossils are found. 



Anomia simplex if or mis sp. n. PI. VIII, fig. 10, 11. 



Shell subovate and prolonged in the region of the beak ; left 

 valve very globose, nearly equilateral, somewhat irregular; 

 beak located in median dorsal portion of the shell, submarginal," 

 slightly projecting and incurved ; surface without plications 

 or ornamentation, except possibly very faint indications of 

 concentric lines of growth. 



* Palaeontology of California, vol. ii, p. 177, pi. xxix, fig. 63. 

 fMd. Geol. Sur., Eocene, p. 163, pi. xxxii, figs. 1, la, 2, 2a, 2b. 



Am. Jour. Sci — Fourth Series, Vol. XX, No. 117. — September, 1905. 

 16 



