WHITEAVE6.J LARAMIE AND CRETACEOUS INVERTEBRATA. 83 



F. EXACT GEOLOGICAL HORIZON I'NCERTAIX. 



" The species included under this general title are from several 

 localities in the Foot-Hills and Rocky Mountains where the beds are 

 much disturbed, and as the sections have not yet been worked out in 

 detail there is no satisfactory stratigraphical evidence as to the posi- 

 tions which these deposits occupy in the series.'' G. M. Dawson. "With 

 the exception of the first-named, which' is possibly from the Laramie 

 Formation, the whole of the species are undoubtedly Cretaceous. 



LA]*IELLIBRAXCHIATA. 



OsTREA .suBTRiaoNALis, Evans and Shumard. 



Ostrea ittihlrigonali'^, Meek. 1876. (But doubtfully as of E. and S.) Rep. U. S. 

 Geol. Surv. Terr., vol. IX., p. .510, pi. 40, figs. 1, a. b, c, d. 

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

 Xon-Marine Foss. :Mo11. N. Am., Washington, 1883. 



Middle Fork of the Old Man River, about two miles above the mouth 

 of the Xorth Fork, G. M. Dawson, 1883 : a number of specimens of 

 the shell of a small oyster which appear to be referable to this species. 



These shells are not quite as typical forms of 0. subtrigonalis as those 

 from the "Belly River indicated under that name on page 30, and some 

 have very much the appearance of small examples of Ostrea glabra, 

 especially of the variety arcuatiUs, Meek. It may be that both species 

 are represented at the locality first mentioned. 



Ostrea congesta, Conrad. 



Ostrea congeda, Conrad. 1843. Nicollet's Rep. of Expl. in the Northwest, p. 107. 

 Hall and Meek. 1854. Mem. Am. Ac. Arts and Sc, Boston, vol. 

 VIII. (n. s.), p. 405. 



Meek and Hayden. 1856. Proc. Ac. Nat. Sc. Phil, p. 286. 

 Hall. 1856. Pacific E. R. Reports, vol. IIL, p. 100, pL 1, fig. 11. 

 Meek. 1876. Rep. U. S. Geol. Sur\'. Terr., vol. IX., p. 13, pi. 9, 

 figs. 1, a, b, c, d, e, f. 



Waterton River, a few miles below the lake, G. M. Dawson, 1881 : 

 about half a dozen badly presei-ved specimens. 



