1903.] STANTON—MOLLUSCAN FAUNULE. 195 
UNIO DouGLAssiI n. sp. Pl. IV, Figs. 3, 4. 
Shell below medium size, elongate, rather slender and moder- 
ately convex; beaks small, inconspicuous, situated about one- 
fourth the length of the shell from the anterior end ; dorsal margin 
nearly straight ; ventral margin very gently convex ; anterior end 
regularly rounded ; posterior end broadly rounded below and very 
obliquely subtruncate above, so that its termination is acutely sub- 
angular ; umbonal region strongly sculptured over an area about 
17 mm. long and 7 mm. high, with prominent concentric ribs, 
crossed on the posterior portion by two sharply elevated, linear, 
radiating ribs, one of which is on the umbonal ridge and the other 
midway between it and the postero-dorsal margin. The con- 
centric ribs change their direction abruptly and have their con- 
tinuity more or less broken in crossing the radiating ribs, especially 
the upper one. The rest of the shell shows only moderately dis- 
tinct growth-lines, except on the postero-dorsal area above the 
umbonal ridge, which shows numerous faint, slightly curved, irreg- 
ular radiating lines. 
An average specimen measures 56 mm. in length, 24 mm. in 
height and 15 mm. in convexity (both valves), the greatest height 
and convexity being about midlength of the shell. A few speci- 
mens appear to be relatively somewhat more compressed and higher, 
but this is due, in part at least, to accidental distortion. The 
species is represented by about forty specimens. 
This species closely resembles Uno vetustus Meek from the Bear 
River formation in all the details of sculpture, but it differs from 
that species in its smaller size and much more slender form. 
Locality.—Wettacombe’s ranche near Musselshell River, in the 
vicinity of Harlowton, Montana. 
Horizon.—Upper part of Lower Cretaceous or base of Upper 
Cretaceous. 
VIVIPARUS MONTANAENSIS n. sp. Pl. IV, Fig. 5. 
Shell small, rather stout, subovate, consisting of about five 
rapidly increasing whorls ; volutions rounded below and obtusely 
subangular and flattened above, so that they are more or less dis- 
tinctly shouldered ; last volution slightly expanded at the aperture, 
which is broadly ovate ; outer lip simple, nearly straight in profile 
outline; inner lip moderately thick, closely appressed to the shell 
above, very slightly elevated and reflexed below; surface bearing 
only very fine lines of growth. 
