THE NAUTILUS. 139 



for examination by Dr. H. A. Pilsbry, measure 1.70 x .6 mm., and 

 the lot from Kent, O., from which Dr. Pilsbry defined this species, 

 NAUTILUS, Vol. VIII, p. 63, measure 1.75 x .6 mm. 



The average size of 0. exile from a large series of measurements 

 may be put down as 1.75 x .6 mm. 



The northern race is, so far as I have seen, confined to the 

 so-called " Canadian Zone," and I therefore propose the name C. exile 

 canadcnse for this variety, taking shells collected at Kennebunkport, 

 Me., as the types. These measure 2.1 x .75 mm., which is about 

 the average size. The series of measurements below show the slight 

 variation in this variety : 



Kennebunkport, Me. (types), 2.1 x .75 mm. 



Islesboro, Me., 2.15 x .75 mm. 



Aroostook Co., Me., 2.00 x .75 mm. 



Hartland, Vt., 2.0 to 2.10 mm. long. 



Bobcaygeon, Ont., Can., 2.00 x .70 mm. 



Ottawa, Ont., Can., 2.10 x .65 mm. 



Winnipeg, Manitoba, 2.05 x .75 mm. 



Huron Mtn., Marquette Co., Mich., 2.05 x .75. 



Lime Id., Chippewa Co., Mich., 2.0 to 2.1 mm. long. 



Gogebic Lake, Ontanogen Co., Mich., 2.0 to 2.1 mm. long. 



White Earth Lake, Minn., 2.1 mm. long. 



The Ottawa shells are the most slender that I have seen. 



All of the Michigan C. exile in the collection of Mr. Bryant 

 Walker are var. canadense with the exception of one lot from Shelby, 

 Macomb Co., which measures 1.75 to 1.80 mm., and a lot from Sag- 

 inavv where they run from 1.7 to 1.9 mm. 



The only southern shells which I have seen approaching var. can- 

 adense in size is a lot collected by Herbert H. Smith in mountain 

 forests near Princeton, Ala. These measure 1.90 x .70 mm., and 

 are unusually heavily ribbed, but other shells collected in the same 

 general locality are typical exile. 



Plate VIII, where the figures are magnified 18 diameters, shows the 

 difference in size very plainly. 



C. exiguum also appears to run somewhat larger in the North, but 

 as there is more variation in this species than in exile, the northern 

 race is not well defined. The average size of exiguum is about 1.75 x 

 .75 mm., but there is a wide variation as shown by measurements 

 given below : 



