640 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. 



CEPHALOPODA. 



Scaphites cf. ventricosus Meek and Hayden. 



A mere fragment from Glade Creek, resembling this species in sculp- 

 ture. (See p. 636.) 



Placenticeras placenta (DeKay)? 



Ammonites placenta DeKay, 1827 : Ann. New York Lyceum Nat. Hist., Vol. II, p. 278, 



PI. Y, fig. 3. 

 Placenticeras placenta (DeKay) Meek, 1876: Sept. U. S. Geo]. Surv. Terr., Vol. IX, 



p. 465, PI. XXIY, figs. 2«, b. 



A fragment probably belonging to this well-known species was 

 collected near the second crossing of the Snake River. The species is 

 abundant and widely distributed in the Montana formation and its equiva- 

 lents, and a few specimens of it, or of a very closely related species, have 

 been obtained in the Colorado formation. 



