MESOZOIC FOSSILS. 633 



Valley, Montana. Other examples were obtained in the Gallatin Range 

 and at several points in the northwestern part of Yellowstone National Park 

 from fresh-water beds of the Cretaceous section of that region. 



GoNIOBASIS? INCREBESCENS 11. sp. 

 PI. LXXV, fig. 7. 



Shell of about the same length as the preceding, but more robust 

 in form, consisting of only about fire rapidly increasing convex whorls ; 

 surface nearly smooth, with fine lines of growth ; other features, as far as 

 known, the same as in G.I pealei. 



Length of an average specimen, 13 mm.; breadth of body whorl, 

 7.5 mm. 



Nearly all the specimens are in the form of imperfect internal casts 

 retaining portions of the shell, but of course not showing the generic 

 features fully. It seems to be related to G% pealei. 



The type is from the same horizon as the preceding on Fawn Creek, 

 and it occurs in this bed at several localities in that region. 



Amnicola? ceetacea n. sp. 

 PL LXXV, fig. S. 



Shell small, conical, consisting of four or five rapidly increasing con- 

 vex whorls ; suture deeply impressed ; surface marked only by lines of 

 growth; aperture oval. 



Height, 9 mm.; breadth of last whorl, 6 mm. 



Occurs with the preceding species on Fawn Creek. 



COLORADO FORMATION. 

 PELECYPODA. 



Ostrea anomioides Meek. 



Ostrea anomioides Meek, 1873 : Ann. Rept. U. S. Geol. Surv. Terr, for 1872, p. 488. 

 White, 1880: Idem for 1878, p. 10, PI. XI, figs. 4a, b. 1884: Fourth Aim. Rept. 

 U. S. Geol. Surv., p. 291, PI. XXXIX, figs. 4 and 5. Stantou, 1894: Bull. LT. S. 

 Geo). Surv. Xo. 106, p. 55, PI. I, figs. 5 aud 6. 



This species, which was originally described from the Missouri River 

 below Gallatin, Montana, is abundant in sandy shales near the base of 



