MEXICAK BOUNDARY LINE. 



147 



BIVALVES. 



CAPRINA, D'Orbigny. 



CAPRINA OCCIDENTALIS. 



Plate II, Figure 1, a, h, c. 



Caprina occidentalis, Con. Proc. Acad. Nat. Sci. vol. VII, p. 268. 



Falcate, flattened on the side of the outer curve, convex on the opposite, the other margins 

 acutely rounded ; surface very obscurely striated transversely, substance coarsely fibrous. 

 Locality. — Near the mouth of Puercos river. 



CAPRINA PLANATA. 



Plate II, Figure 2, a, b. 

 Caprina flanata^ Con. Proc. Acad. Nat. Sci. Vol. VII, p. 268. 



Flattened on one side and convex on the opposite, milch compressed, very long and narrow, 

 falcate, fibrous, and exhibiting small septa. 



A fragment of a valve, two feet in length, and another smaller fragment, are all of this 

 species that I have seen. The cavities between the septa are lined with crystals of carbonate of 

 lime, and both this and the preceding species are imbedded in white friable limestone. 



Locality. — Oak creek, near Puercos. 



TEREBRATULA, Lhwyd. Lam. 

 TEREBRATULA WACOENSIS. 



Plate III, Figure 1. 

 Terebratula Wacoensis, Roemer, Kreide. von Texas, p. 81, pi. VI. 



Inflated, semi-globose, pentagonal, smooth ; front margin straight, not inflated, dorsal valve 

 most convex; umbo obtuse, slightly incurved; area sufficiently distinct, circumscribed by an 

 obtuse angle ; ventral valve suborbicular, regularly convex ; surface minutely punctate. 



Locality. — 



TEREBRATULA CHOCTAWENSIS. 



Terebratula Cliodatuensis, Shumard, Geol. of Red river, p. 207, pi. II, fig. 3. 

 Suboval, truncated at base ; both valves ventricose, surface elegantly marked with minute 

 punctiB. 



Locality. — Leon Springs. 



TRIGONIA, Lam. 



This interesting genus has been found as far down in the geological series as the triassic 

 rocks. D'Orbigny enumerates ninety-nine species, and although there is one living representa- 

 tive on the coast of Australia yet the genus is unknown in the strata of tertiary periods. 



