136 THE NAUTILUS. 



umellar insertion of the lip is on the base of the preceeding whorl 

 between the umbilicus and the lower carina (fig. 7), which thus 

 forms a strong spirally entering fold slightly below the centre of the 

 inner margin. Compared with this species, P. trivolvis is distin- 

 guished by its greater width in proportion to its height, wider and 

 more convex whorls, finer and closer stria?, wider and more oblique 

 aperture, less prominent superior carina, which is nearly central on 

 the penultimate whorl, the constantly rounded base of the whorls in 

 all stages of growth, never sharply and acutely carinate as in corpu- 

 lenlus ; and smaller umbilicus, not exhibiting the apical whorls. 

 The specimens before me are from the following localities : 



1. Michigan. Coll. University of Michigan (figs. 1, 2 and 3). 

 Exact locality and collector unknown. These specimens have 



been in the University museum for many years, and no further infor- 

 mation in regard to them is attainable. They are much heavier and 

 thicker than those from the other localities represented, but are other- 

 wise very similar. In all probability they were part of the material 

 turned into the museum from one of the early geological surveys, and 

 quite likely are from the western part of the Upper Peninsula, as noth- 

 ing like them has been found in the upper part of the Lower Penin- 

 sula, or in the eastern portion of the upper. They were originally 

 catalogued as P. trivolvis Say. 



2. Rat Portage, Keewatin, Manitoba. 



Coll. Fred'k Stearns. Collected by A. C. Lawson in 1884. 



3. Vermillion Lake, Minn., (fig. 4, 5 and G). 



Received from H. F. Nachtrieb of the Geol. and Nat. Hist. Sur- 

 vey of Minn. 



4. Vermillion Lake, Hudson Bay Territory (fig. 7.) 



From the collection of the late Dr. James Lewis. Collector un- 

 known. 



Mr. J. F. Whiteaves, of the Geological Survey of Canada, has 

 kindly furnished the following data in regard to the material belong- 

 ing to the Survey : 



" In the Museum of the Geological Survey of Canada, there are 

 five typical examples of Planorbis corpulentus collected by Dr. James 

 Fletcher, in 1882, at the Lake of the Woods; by A. C. Lawson in 

 1884, at Rat Portage, above the Falls, and by W. Mclnnes in 1890, 

 at Green water Lake, Thunder Bay District. There are also speci- 

 mens which are at least very similar to P. corpulentus in the same 



