MESOZOIO FOSSILS. 639 



Mactra warrenana Meek and Hayden. 



Mactra warrenana Meek and Hayden, 1856: Proc. Acad. Xat. Sci. Pkila., p. 271. 

 Mactra (Gymbophoraf) warrenana (M. and H.) Meek, 1876: Eept. U. S. Geol. Surv. 

 Terr., Vol. IX, p. 208, PI. XXX, figs. la-d. 



Casts in sandstone apparently belonging to this species are abundant 

 near Glade Creek. The species is widely distributed in the Montana 

 formation. 



Mactra arenaria Meek? 



Mactra (Trigonellaf) arenaria Meek, 1877: U. S. Geol. Expl. 40th Parallel, Vol. IV, 

 Pt. I, p. 154, PI. XIV, fig. 5. 



This species is abundant in the Montana formation at Coalville, Utah. 

 A single cast that seems to belong to it is associated with the preceding 

 species near Glade Creek. 



GASTROPODA. 



Gyrodes depressa Meek. 



Gyrodes depressa Meek, 1877 : U. S. Geol. Expl. 40tb Parallel, Vol. IV, Pt. I, p. 159, 

 PI. XV, figs. 1, 1ft. Stanton, 1894: Bull. U. S. Geol. Surv. Xo. 106, p. 135, 

 PI. XXIX, figs. 11-14. 



Common in the sandstones on Glade Creek. It was originally 

 described from the Colorado formation at Coalville, Utah, and is found at 

 the same horizon in Huerfano Park, Colorado. The genus Gyrodes has 

 not hitherto been reported from the Montana formation of the Rocky 

 Mountain region, but it is well represented in beds of the same age in the 

 Atlantic and Gulf border region. In fact, Gyrodes petrosa (Morton) from 

 the Ripley formation is scarcely distinguishable from G. depressa. 



Cerithium! sp. 



A small, slender form of doubtful affinities, represented by an internal 

 cast from sandstone on Huckleberry Mountain. 



Pyrula? sp. 



A fragmentary cast from Glade Creek. 



