MEXICAN BOUNDARY LINE. 141 



DESCKIPTIONS OF CKETACEOUS AND TERTIARY FOSSILS. 



BY T. A. CONRAD. 



The organic remains in the collection of the Boundary Survey are chiefly cretaceous shells, 

 which I have carefully compared with the Alabama and New Jersey species ; and out of more 

 than one hundred species in Roemer's and the Survey collections, I can find only two that may be 

 considered identical with New Jersey species. These are Exogyra costata and the Ostrea vesi- 

 cular is oi Lam. , vfhich. is at least a marked variety, termed ancella hy 'Roemer . D'Orbigny 

 places some of Roemer's Texan species in the same division to which he refers all the New Jersey 

 species, the Senonian stage ; yet I think there is sufficient evidence that the cretaceous strata of 

 Texas are not exactly synchronous Avith those of New Jersey, or of Alabama, while those of the 

 latter State appear to form a passage or intermediate stage between the cretaceous strata of the 

 two former states, which, besides the Exogyra and Ostrea above mentioned, have four other 

 species in common, viz : Gryphcea Pitcheri, Trigonia thoracica, Morton, Baculites anceps, and 

 B. asper. 



Among these interesting fossils, those from Leon Springs are conspicuous for variety and 

 beauty, and unequivocally mark the cretaceous period. There is not the slightest trace of the 

 Jurassic or any formation older than the grand epoch of the chalk. A few interesting fossils 

 from near the mouth of Puercos river are imbedded in a white, chalky limestone, and, with the 

 exception of Ammonites Texanus, are peculiar !o this locality, in the present state of our col- 

 lections. There is a specimen of flint from Leon Springs of the horn-shaped form so comnion in 

 the chalk of Europe. 



A few Eocene shells collected by Mr. Schott, of the age of the Claiborne formation, prove that 

 Eocene strata occur in western Texas. 



. Eocene species. 



Cardita planicosta, Arroyo Las Minas, between Eagle Pass and Leon. 



Corbula nasuta, Con. 



Cytherea Nuttalli, Con. 



Cassidula alveata. Con. 



Volutilithes Sayana, Con. 



Natica limula, Con. 



Gixtaceous fossils from Oak Creek, Texas, collected hy Arthur Schott. 



Ammonites Texanus, Roemer, near Puercos river. 

 Nerinea Schotti, Con., near the mouth of Puercos river. 

 Caprina occidentalis. Con., near the mouth of Puercos river. 

 C. planata, Con., Oak creek, near Puercos river. 

 Hippurites? n. s., near the mouth of Puercos river. 



