MEXICAN BOUNDARY LINE. 161 



to flat ; cavity shallow and remarkably contracted towards the lunge, which is elongated, having 

 a deep and broad cavity in the lower valve^ with a corresponding rounded and striated ridge in 

 the opposite valve. 



This large oyster measures nearly two feet from beak to base. The contracted form of the 

 cavity is most striking in the oldest individuals. Probably a Miocene shell. 



Locality. — Oyster Point, Mexico. 



ANOMIA, Lin. 

 ANOMIA SUBCOSTATA. 



Plate XIX, Fig. 1 a, h. 



Anomia subcostata, Con. Proc. Acad. Nat. Sc, vol. VII, p. 267. 



Obtusely ovate, rather thick ; umbo of larger valve ventricose ; hinge thickened, surface of 

 the valve obtusely undulated concentrically, and marked with waved, wrinkled, interrupted 

 ribs, much raised, except towards the base, where they are larger and somewhat tuberculiform ; 

 upi^er valve entire, or with obsolete radii towards the base. 



This has a general resemblance to A. Rufflni, Con., of the Virginia Miocene, but is much 

 thicker and very distinct. 



CAKDITA, Lam. Plain. 



CARDITA PLANICOSTA. 



Plate XIX, Figxtrb 2, a, h. 



Venericardia planicosta, Lam. An. sans Vert., vol. V, p. 



669. Deah. Coq. Foss., vol. I, p. 149. 

 Vardita planicosta, Blainville. 



Ovate-oblique, cordate, very thick, with flattened broad ribs, 22-24, granulated towards the 

 apex ; lunule very profound, wide, cordate, margin crenate within, cardinal teeth two, finely 

 striated. 



This species is found in Virginia and Alabama, as well as in California. Deshayes describes 

 the Paris specimens of C. planicosta as crenulated on the ribs near the summit, a character 

 scarcely visible in the specimens that I have examined. 



Locality. — Arroyo las Minas, between Eagle Pass and Leon. 



CORBULA, Lam. 

 CORBULA NASUTA. 



Plate XIX, Figure 4. 



Corbula nasuta, Con. Foss. Shells of Tert. Form. 

 Corhula Alahamiensis, Lea, Cont. p. 45, pi, I, fig. 12. 



* ■ 



Inflated, triangular-ovate, very inequivalve, ventricose ; finely striated concentrically ; buccal 

 end rounded, longer than the anal, which is contracted ; flexuous, narrow, and obliquely trun- 

 cated at the end. 



Locality. — Western Texas. 

 21 M 



