129 



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. In- 

 habits 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 interest- 

 ing terrestrial and fluviatile shells, on our return to the settlements, 

 and I am indebted to the liberality of Dr. Bigsby for the indi- 

 vidual above described. It is closely allied to trivolvis, nobis, but 

 is much less rounded on the sides of the whorls, the carinae are 

 more prominent, the upper side is much more horizontally flattened, 

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

 higher in proportion to its width, and the aperture extends both 

 above and below the penultimate whorl. 



Planorbis campanulatus, nob. Falls of Niagara. 



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

 Niagara. 



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

 west Territory, and may be found in plenty crawling upon the rocks 

 near the shores. They vary in size from those found in the Eastern 

 States, being less than half as large. 



Planorbis armigerus, nob. St. Peter and Red rivers, com- 

 mon. 



Planorbis bicarinatus, nob. North-west Territory, rather 

 common. 



Lymneus megasomus. — Large, dilated suboval; spire short, 

 rapidly diminishing, acute ; whorls about five, rounded, obtusely 

 wrinkled across ; body-whorl large, the wrinkles very obvious ; 

 suture deeply impressed ; aperture subovate, much longer than the 

 spire, within chesnut-brown ; collumella white. 



Length more than one and six-tenths of an inch. Length of 

 the aperture more than one inch. Greatest diameter one inch. 



This remarkably large and fine species was found in Bois Blanc 

 Lake, North-west Territory, by Dr. Bigsby, to whom I am indebted 

 for specimens. The color is brownish, sometimes lineated across 



* [Plate 74 of tMs reprint.— Ed.] • 



