354 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Odonlobasis ven- 



triosa. 

 A dorsal view, 



.species, I would propose for that here under consideration the name Odonlo- 

 basis humerosa, and in that ease this latter form, as already explained, would 

 become the type of the genus, as the generic characters were taken from it. 

 Locality and position. — Deer Creek, on the north branch of Platte 

 River; from the Fox Hills group of the Upper Missouri Cretaceous series. 

 The original type-specimen of Fusus constrictus was found at near the same 

 horizon, on Sage Creek, Dakota. 



O <1 o ii t o l> a s ■ s ventriosa, Meek. 

 Plate 19, figs. 1, a,b,c. 



Fi s- 43 - Shell subfusiform, with spire about equaling four-fifths 



the length of the aperture and canal; volutions six and a half, 

 evenly convex, each provided with sixteen to eighteen little 

 vertical folds, that become less distinct and more irregular 

 on the body-turn, which is ventricose, and contracts abruptly 

 to the beak below; suture linear and rather distinctly im- 

 pressed; aperture rhombic-obovate, being angular above, 

 more convex on the outer than the inner side, and tapering 

 enlarged to show abruptly into the little, short, oblique canal below; columella 



the tooth-like pro- 

 jection at the base and revolving sulcus- typical ; entire surface ornamented by 



of the outer ii P . moderately distinct lines of growth, crossed by little, flattened, 

 revolving, band-like lines, wider than the linear furrows between, one of the 

 former of which is a little larger than the others at the upper edge of the 

 volutions, so as to give the suture a slightly banded appearance. 



Length, 0.46 inch; breadth, 0.26 inch; slopes of the spire straight, 

 with a divergence of about 46°. 



This species will be readily distinguished from the last, by its more 

 evenly rounded volutions, particularly the last one, which is almost entirely 

 without the constricted and obscurely-shouldered appearance of that shell. 

 Its vertical folds are also smaller and more numerous on all of the volutions, 

 and become less distinctly defined and more irregular on the last one. The 

 revolving bands, or flattened lines, are also proportionally a little wider. 

 Again, it differs in the form of the aperture, which is proportionally wider, 

 being more convex on the outer side. I know of no other shell with which 

 it need lie compared. 



Locality and position. — Cherry Creek, near the mouth of Sage Creek, 

 Dakota; from the upper part of the Fort Pierre group: 



