186 CONTRIBUTIONS TO CANADIAN PAL/EONTOLOGT. 



" preserved only on the margins " and the beak either obliterated or 

 covered by the matrix. In both the lateral margins are nearly straight 

 and parallel and the front border is subtruncate, so that although the 

 type of Hall and Meek's species is said to be from the Fort Pieri'e 

 group (near Eed Cedar Island, on the Upper Missouri Eiver,) and the 

 specimens obtained by Mr. Tyrrell are from a distinctly lower horizon 

 in the Cretaceous, no essential differences can at present be detected 

 between them. 



MOLLUSCA. 



LAMELLIBKANCHIATA. 



OsTREA coNGESTA, Conrad. 



Ontrea congesta, Conrad. 1843. Nicollet's Rep. Expl. in the N.W., p. 167.— Hall 

 & Meek (1854) Mem. Am. Aoad. Arts & He, Boston, vol- VIII. 

 (N. S.), p. 405.— Meek & Hayden (Nov., 1856) Proc. Ac. Nat. Sc 

 Phil., p. 286.— Hall (1856). Paciiic R.R. Re pts., vol- HI., p. 100, 

 pi. 1, fig. 11.— Meek (1876). Rep: U. S. Geol. Surv. Terr., vol. IX. 

 p. 13, pi. 9, figs. 1 a, f. 



Swan Eiver, J. W. Spencer, 1814. 



Ochre Eiver, Township 23, Eange 17 W., and Township 22 in the 

 same Eange ; Vermilion Eiver, Township 24, Eange 17 W., and Town- 

 ship 25 in the same Eange; Eolling Eiver, two miles above the old 

 C.P.E. crossing, and Swan River, Township 35, Eange 29 W. ; J. B. 

 Tyi-rell, 1887. 



Thunder Hill, Township 35, Eange 30 W. ; D. B. Bowling, 1887. 



Assiniboine Eiver, Section 30, Township 8, Eange 11 W. ; Warren 

 Upham, 1887. 



From each of these localities a few specimens, which arc apparently 

 referable to this widely distributed species, were collected from the 

 Niobrara group, or upper part of the sei'ies. Most of these specimeus 

 are less than an inch in their greatest diameter, though they occasion- 

 ally attain to a length of an inch and a half or an inch and three- 

 quarters. In each of those from Thunder Hill the lower valve is 

 attached to a fragment of a large Inoceramus, and the onlj' example in 

 which the shells are clustered is from the Eolling Eiver. All the rest 

 appear to be both single and unattached to any foreign body, though 

 fully one half of the specimens are upper valves. The wi'iter has not 

 yet seen, either from Manitoba or from any othei' part of Canada, any 

 specimens of 0. congesta whicli correspond with that form of the 

 species described and figured by Meek in which the margins of the 

 lower valves ai'C " abru))tly deflected upward at right angle.-* to the flat, 



