120 [June, 



of fold at its junction with the outer lip below. Length about 1 inch ; breadth 

 57 inch; length of aperture -55 inch, breadth of do. -26 inch. 



It is probable the above description will have to be modified somewhat, when 

 perfect specimens are obtained, as all those we have seen are more or less 

 broken. 



Locality. Three miles below Fort Union. 



Physa subelongata. 



Shell elongate ovate ; spire elevated, acute at the apex ; volutions about six 

 and a half, nearly flat ; suture oblique, linear, scarcely distinct ; surface faintly 

 marked with lines of growth; aperture unknown; columella twisted into a kind 

 of fold below the impressed umbilical region. Length 1-16 inches ; breadth -53 

 inch ; length of aperture about -57 inch ; apical angle very convex, divergence 

 49''. 



This Physa belongs to the same type as two or three elongated species de- 

 scribed by Matheron, from the Great Lignite formations of the south of France, 

 (^Catalogue Methodique, &c., pi. 36.) It differs, however, from his P. Gardanennis, 

 which it most neirly resembles, in having much flatter volutions, a le-s dis- 

 tinctly impressed suture, and relatively smaller body whorl. Our specimen is 

 so much broken and worn, that if there were other markings than those pre- 

 served they would have been obliterated. 



Locality. Bad Lands of the Judith. 



Planorbis subumbilicatus. 



Shell very small, subdiscoidal ; spire flat ; volutions two and a half to three, 

 nearly cyliudrical ; surface marked with very fine, rather indistinct lines of 

 growth ; sutures strongly defined ; umbilicus large, showing the volutions to the 

 apex ; aperture round or obliquely a little oval. Larger diameter -IS inch ; 

 smaller do. -14 inch. 



Locality. Three miles below Fort Union. 



Planorbis convolutus. 



Shell large, discoidal, nearly equally concave, and exhibiting all the whorls on 

 both sides ; volutions slightly embracing, very strongly separated by the sutures, 

 more broadly rounded on the right than on the left side ; surface (of cast) 

 having faint undulations parallel to the obsolete lines of growth, which pass 

 round very obliquely forward from the right to the left ; aperture ovate, nar- 

 rower on the left than the right side, slightly concave within, for the reception 

 of the succeeding whorl ; right lip projecting considerably beyond the left. 

 Greater diameter 1.01 inch ; smaller do. .32 inch. 



In its general appearance this species approaches P. rotundatus of Brong., but 

 is much less compressed. It differs also in the form of the aperture, which is 

 wider than high, while that of P. rotundatus is higher than wide (See Deshays' 

 Coq. foss. pi. 9, fig. 7 and 8.) 



Locality. Little Horn river. 



Velletia (Ancylus) minuta. 



Shell minute, ovate or elliptical-pattiform, exceedingly thin and fragile; ex- 

 tremities rounded ; anterior end apparently a little wider than the posterior ; 

 apex moderately elevated, obtuse, nearer the posterior end than the middle, 

 turned to the left ; front slope convex ; posterior and postero-sinistral slopes 

 concave, dextral convex ; surface marked with fine concentric striic. Length 

 .08 inch ; breadth .06 inch ; height .03 inch. 



Resembles Velletia elegaiis of Edwards, {Ancylus elegans of Sowerby, Min. Conch, 

 pi. 533) but is much smaller, and wants the radiating striae of that species. 



Locality. Three miles below Fort Union. 



Paludina mcltilineata. 

 Shell conical-ovate, rather thin ; spire elevated ; volutions six to six and a 

 half, rounded convex, increasing gradually from the apex ; suture strongly im- 



