28 UNITED STATES GEOLOGICAL SUEVEY— TERTIAKY FLORA. 



salt enough to have permitted the existence of Inoceramvs, Anchura, and Gy- 

 rodes, it" not of some or all of the genera mentioned above. Indeed, at Coal- 

 ville we find Inoceramus associated with some brackish-water types, and the 

 additional Cretaceous genera Cypritnera, Anchura, Gyrodes, etc., in closely 

 associated beds." 



"When we come to consider the invertebrate fossils yet known from this 

 formation in their specific relations, we find all, with possibly two or three 

 exceptions, new to science, and different from those yet found either at Bear 

 River, Coalville, or indeed elsewhere in any established horizon ; so that we 

 can scarcely more than conjecture from their specific affinities to known forms 

 as to the probable age of the rocks in which we find them. Considered in 

 this respect, their evidence, however, is conflicting. Two of the species of Cor- 

 bula for instance (C tropidophora and C. undiferd) are most similar to species 

 found in the brackish-water beds at the mouth of Judith River in the Upper 

 Missouri, that we liave always considered Lower Tertiary, though there are 

 some reasons for suspecting that they may be Upper Cretaceous. A Corhicula' 

 both from the Black Buttes and Point of Rocks localities is even so very 

 nearly like C. cylheriformis from the Judith River beds that I have referred it 

 doubtfully to that species." 



"Again, the species Anomia gryphorhynchus, found so abundantly at 

 Point of Rocks in the same bed with the above-mentioned Corhicula and 

 Corbula tropuiophora, so closely resembles a Texas Cretaceous shell described 

 by Roemer under the name Ostrea anomiceformis that I am strongly inclined 

 to suspect they may be the same; though whether identical or not, at least 

 our shell is certainly not an Oyster, as it has its muscular and cartilage scars 

 precisely as in Anomia, while its beak is never marginal, and it has no liga- 

 ment-area. In all of these (and indeed in all other characters), the Texas 

 shell as illustrated by Roemer seems to agree precisely with ours, excepting 

 that he represents it as having only one central muscular scar instead of three. 

 In many of our specimens, however, the two smaller of these scars are very 

 obscure, and might be easily overlooked. It is true he figures a nearly flat 

 valve, without any byssal perforation, and a convex one as opposite valves, and 

 if they are such the shell would certainly not be an Anomia. Among a large 

 collection of our shells, including thousands of specimens, however, I have 

 not yet seen a single perforated valve, though they vary much in convexity, 

 some of the valves being nearly as depressed as the one Roemer figures as 



