364 EXPLOEATIONS ACROSS THE GREAT BASIST OF UTAH. 



aperture subovate, narrowly rounded below and angular above, scarcely equaling half 

 the entire length of the shell; surface marked by fine obscure lines of growth. 



Length, 0.40 inch; breadth, 0.20 inch; apical angle convex, divergence about 40°. 



This is a neat little shell, quite unlike any other species known to me from the 

 Bear River beds. In several respects, it resembles some recent species, but it still dif- 

 fers too clearly to be confounded with any of them, even if its geological position did 

 not preclude its identification with any existing species. The specimens do not show 

 the columella very clearly, and I have not been able to see on it the characteristic fold 

 of Limncea quite satisfactorily; but, on re-examination, I am more inclined to believe 

 that it belong to that genus than to any of the Melanian groups. 



Locality ami posifimt. — Bear River fresh-water beds, at mouth of Sulphur Creek, 

 Wyoming. 



Genus RHYTOPHORUS. 



Rhytophorus pkiscus, Meek. 



Plate 5, fig. 4, a,%. 



Shell oval, moderately thick; spire depressed-conical; whorls about five, convex 

 or subangular, last one comparatively large, shouldered above, and tapering below the 

 middle; suture well defined; surface marked by rather obscure lines of growth, and 

 small, regular, vertical, or slightly oblique folds, which are distinct on the spire and the 

 upper part of the body, but obsolete below; aperture narrow, angular above, and nar- 

 rowly rounded below; outer lip apparently sharp, and without teeth or crenuhitions 

 within; columella provided with one rather strong oblique fold below, and a much 

 smaller less oblique one about half-way up the aperture. 



Length, near 0.77 inch; breadth, 0.50 inch; apical angle nearly regular, diverg- 

 ence about 80°. 



This shell is very unlike any other fossil yet known in any of the fresh-water or 

 estuary deposits of the West or Northwest, and differs materially from any recent species 

 of which 1 have any knowledge. 



Since writing the above, I have proposed a new genus, Rhytophorus, for its reception. 



Locality awl position. — Fresh-water or estuary beds on Bear River, near mouth of 

 Sulphur Creek, latitude 41° 12' north, longitude 110° 52' west; probably latest Cre- 

 taceous. 



TERTIARY FOSSILS. 



M0LLDSCA. 



LAMELLIBRANCHIATA. 



Genus UNIO, Retzius. 



Unio Haydeni, Meek. 



Plate 5, fig. 11, a, b. 

 Unio Haydeni (July, 1860), Proceed. Acad. Nat. Sci. Philad., XII, 312. 



Shell under medium size, subelliptical, rather thin, moderately convex; extremities 

 more or less regularly rounded, the posterior margin being sometimes obliquely subtrun- 



