306 FOSSIL OSTREID^ OF NORTH AMERICA. 



c. It has also beeu fouud in New Mexico, and iu the State of Niievo 

 Leou, Mexico. It is a well marked and not very vaiiable species. 



Exogyra Matheroniana d'Orbigny. 



Conrad, in the Keport of tbe United States and Mexican Boundary 

 Survey, referred certain si)ecimens to this species tbat are specifically 

 identical witb tbe form tbat Professor licenier described under tbe name 

 of Exogyra texarin. (See reniaiks under tbat bead in a following para- 

 grapb.) It is a soniewbat common iorm in tbe Cretaceous of Texas and 

 tbe adjacent parts of Mexico. 



Exogyra pUcai a Lamarck. 



It is doubtful wbctber this species exists in North American rocks. 

 Certain authors have placed specimens under this name which I believe 

 to belong to tbe E. texana of Eoemer. (See remarks under tbat bead iu 

 a followiujj paragraph.) 



Exogyra ponderosa Kcemer. 



(Plate L, Figs. 1,2, 3.) 



This massive form is common in certain Ceretaceous strata of the 

 States which border the Gulf of Mexico; extending westward into the 

 Ee[)nblic of Mexico. It was first published by Kcemer in Kreidebildung 

 von Texas, page 71, Plate IX, Figs. 2, a, b. As before remarked, it has 

 by some authors been regarded as not specifically different /rom E. cos- 

 tata Say. Tbe two forms are certainly closely similar, but their surface 

 characters are apparently constant in their difference, even when they 

 are fouud associated in the same stratum. The lower valve of this 

 species is very massive in old examjjles, sometimes reaching nearly two 

 inches in thickness of solid shell substance. 



Exogyra parasitica Gabb. 



(Plate LV, Figs. 3,4.) 



Mr. Gabb published this form iu Paleontology of California, Vol. I, 

 page 205, Plates 2G and 31. It is interesting because of the very slight 

 representation that Exogyra has in the Cietaceous strata of the Pacific 

 coast. 



Exogyra iexana Roemer. 



(Plate LI, Figs. 1,2,3,4,5.) 



Professor Eoemer published this species in Kreidebildung von Texas^ 

 page G9, Plate X, Figs. 1, «, b, c, d, c. It is not unfrequently fouud in cer- 

 tain Cretaceous strata in Texas and the adjacent parts of Mexico. It 

 has been by various authors referred to E. p'.icata Lamarck, and E. 

 Matheroniana d'Orbigny. 



