'■i62 APPENDIX, 



2. P. corpulentus. Shell dextral; luhorls more thau 

 three, rather rugged with coarse wrinkles, much higher 

 than wide ; superior surface much flattened, and edged by 

 an abrupt acute line, which is distinct to the aperture ; 

 sides hardly rounded, and terminated below by another 

 abrupt edge, which is not quite so definite and acute as the 

 superior one ; spire slightly concave j umbilicus exhibit- 

 ing a portion of each of the rapidly retiring whorls to the 

 apex; aperture longer than wide, the superior part ex- 

 tending higher than the preceding volution and the inferior 

 portion declining much lower than the inferior line of the 

 same volution. 



Greatest breadth three-fourths of an inch. 



Length of the aperture nearly half an inch. 



Length of the penultimate whorl near the aperture 

 rather more than three-tenths of an inch. 



Inhabits Winnepeek river, Winnepeek lake, Lake of the 

 Woods, and Rainy lake; common. PI. 15, fig. 9. 



Of this species I collected numerous specimens, but had 

 the misfortune to lose them all, as well as a great number 

 of interesting terrestrial and fluviatile shells, on our return 

 to the settlements, and I am indebted to the liberality of 

 Dr. Bigsby for the individual above described. It is close- 

 ly allied to trivolvis, nobis, but is much less rounded on 

 the sides of the whorls, the carinse are more prominent, 

 the upper side is much more horizontally flattened, the la- 

 brum is less rounded, and the whole shell is larger and 

 higher in proportion to its width, and the aperture ex- 

 tends both above and below the penultimate whorl. 



P. canipantilatus, nob. Falls of Niagara. 



P. trivolvis, nob. North-west Territory and Falls of 

 Niagara. 



P. parvus, nob. is common in the waters of the North- 



