30 CONTKIBUTIONS TO CANADIAN PALAEONTOLOGY. 



LAMELLIBEANCHIATA. 



OsTREA PATINA, Meek and Hayden. 



Ostrea patina, Meek and Hayden. 1856. Proc. Ac. Nat. So. Phil., p. 277. 



" " " G. M. Dawson, 1875, Eep. Geol. and Bes. Reg. 



Vicin. 49th Parallel, p. 110. 

 Ostrea (? Oryplicea) patina, Meek. 1876. Eep. U.S. Geol. Surv. Terr., vol. IX., p. 



16, pi. 10, figs. 2a, b — a, b, bis, and 3 e-f, also pi. 11^ 



varieties. 



White Mud Eiver (sometimes called Frenchman's Creek) near the 

 49th Parallel and south of Woody Mountain, G. M. Dawson, 1874, H.M. 

 North American Boundary Commission : abundant and well preserved. 



Ostrea inornata, Meek and Hayden. 



Ostrea inornata. Meek and Hayden. 1860. Proc. Ac. Nat- Sc. Phil., p. 181. 



" Meek. 1876. Kep. U.S. Geol. Surv. Terr., vol. IX., p. 14, pi. 10, 



lig.4. 



St. Mary Eiver, near its confluence with the Belly Eiver, G. M. 

 Dawson, 1881 : one perfect and apparently typical specimen. 



Ostrea subtrigonalis, Evans and Shumard. 



Ostrea suhtrigonaIis,M(i6k. 1876. (But doubtfully as of E. and S.) Eep. U.S. 

 Geol. Surv. Terr., vol. IX., p. 510, pi. 40, figs, la, b, c, d. 

 Figured also on pi. 12, figs. 2-.5, of Dr. C. A. White's Eev. 

 Non-marine Foss. Moll. N. Am., Washington, 1883. 



A number of valves of a small oj^ster which agree perfectly with 

 Meek's description and figures of 0. suhtiigonalis were collected by G. 

 M. Dawson in ISSl on the banks of the Belly Eiver at the mouth of the 

 St. Mary Eiver, in rocks overlying the coal and occupying a position 

 at the base of the shales of the Fort Pierre Group. Similar specimens 

 were collected by Dr. Dawson in 1883 at Milk Eiver Eidge in rocks 

 of precisely the same geological horizon. The Belly Eivei^ specimens 

 are narrowly arcuate and more or less mytiloid in outline, while their 

 lateral margins are usuallyTbut not always minutely crenulated. The 

 lower valve is shallow, and either free or with a small scar of attach- 

 ment, while the upper valve is flat. 



