632 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. 



various localities in Wyoming, is represented in the Yellowstone National 

 Park collection by only a few specimens, from saddle in ridge west of south 

 head of Gardiner; west of Snake River 4 miles south of second crossing 

 and 3 miles south of mouth of Glade Creek. 



CRETACEOUS SPECIES. 



DAKOTA (?) FOKMATION. 1 

 PELECYPODA. 



Unio sp. undet. 



Several casts of a small species of Unio were collected with the gastro- 

 pods named below in Three Forks Valley, Montana, and on Fawn Creek 

 Plateau. The species is doubtless new, but the material is insufficient for 

 description. 



GASTROPODA. 



GoNIOBASIS? PEALEI 11. Sp. 

 PI. LXXY, fig. 6. 



Shell small, slender, eiongate, consisting of about eight convex whorls; 

 apex of spire acute; upper third of each whorl slightly flattened, so that it 

 is most prominent below the middle; suture linear, deeply impressed; 

 surface nearly smooth, being marked only by fine lines of growth, and on 

 some specimens by faint indications of spiral lines. The full form of the 

 aperture is not shown on any of the specimens, but it appears to have been 

 suboval and slightly produced in front. Shell apparently not umbilicated. 



Length of an average specimen with eight whorls, 1-4 mm.; breadth of 

 body whorl, 7 mm. 



This species is very doubtfully referred to Goniobasis, though it seems 

 to be related to G. gracilenta Meek, from the Judith River beds. In general 

 aspect and in the form of the whorls it resembles some recent species of 

 Pomatiopsis, but the form of the aperture and the absence of an umbilicus 

 separate it from that genus. 



The specimen figured was collected by Dr. A. C. Peale in Three Forks 



1 See remarks on pp. 604-605. 



