140 PALEONTOLOGY. 



CEETAOEOUS FOSSILS. 



MOLLUSOA. 



OSTREIDiE. 



Genus OSTEEA, Linn. 



OSTBEA (undt. sp.). 

 Plate 1.5, figs. 10, and 10 a, 1), c. 



Shell of about medium size and thickness, more or less elbngate-sub- 

 ovate, tapering to the beak, which is usually abruptly pointed, and often 

 bent a little to the left or to the right, generally compressed and subequi- 

 valve. Lower valve rather shallow; ligament-area triangular, with its mesial 

 furrow usually deep; surface merely showing appressed imbricating laminae 

 of growth, without any traces of radiating ridges, plications, or striae. Upper 

 valve a little more flattened, or sometimes nearly as convex as the other, 

 but rather less concave within; beak usually more obtuse, and the ligament- 

 area often proportionally a little shorter, with its mesial ri'dge well defined; 

 lateral margins often thickened and crenated near the beaks; surface much 

 as in the other valve. 



Length of a medium-sized specimen, about 2.80 inches; breadth, 1.90 

 inches; convexity of the two valves, about 1 inch. 



In first preparing this report, I merely gave figures of this Oyster with- 

 out a specific name. Subsequently, in revising portions of the report, with- 

 out having the type-specimens at hand for comparison, I was impressed with 

 the similarity of this shell, as figured on our plate, to a species that I had 

 in the mean time described in one of Dr. Hayden's reports from Wyoming, 

 under the name 0. Wyoming ensis^ and placed that name with a mark of 

 doubt opposite its number on the explanations of the plate, while I also in 

 the same way mentioned it in a list of Coalville species. Having since 

 made a direct comparison of the specimens from the two localities, I am led to 

 doubt their specific identity, though they are certainly very much alike. The 

 Coalville specimens have the beak of the under valve less curved upward, 

 and the lateral margins of the only upper valve I have seen from that 



