308 FOSSIL OSTEEID^ OF NORTH AMERICA. 



adelpbia, for 1857, page 136. The type specimens were obtained from 

 the Upper Missouri Eiver region ; and the smoothness which suggested 

 their specific name was not natural, but due to attrition or corrosion. 

 Figures of one of these type specimens are given on plate LVIII. In 

 the Annual Report of theUuited States Geological Survey of the Terri- 

 tories, for 1872, page 508, Mr. Meek described a form from Southern 

 Wyoming under the name of Ostrea wyominfjtnis, figures of which are 

 given on Plates LX and LXI. In the same series of reports, the volume 

 for 1873, page 477, he described another form from the same locality 

 under the name of 0. arcuatUis. Fig. 5, on Plate LIX, is drawn from 

 his type specimen. 



In Powell's Report on the Geology of the Unita Mountains, page 112, 

 I described another form from Southern Wyoming under the name of 

 0. insecuris. Figures of the type specimen are given on Plate LIX. 

 Now, all these forms, as before mentioned, I regard as belonging to one 

 and the same species. 



Ostrea snhtrigonalis Evans & Shumard. 



(Plate LXI, Figs. 4, 5, 6, 7.) 



This small form occurs in the Laramie strata of the Upper Missouri 

 Eiver region. It is not improbable that this also is a variety of 0. glabra, 

 but the somewhat numerous specimens that have hitherto been discov- 

 ered are very uuiform in size and shape, the size being considerably 

 smaller than tbe average of 0. glabra. It was originally published with- 

 out figures ; but it was identified by Meek and illustrated by him in 

 Vol. IX of the United States Geological Survey of the Territories, Plate 

 40, Figs. 1, a,b, c, d. 



