218 



the shell looses its keel and hirsute coat and becomes smooth and 

 sometimes polished. The change thus produced between immature and 

 mature shells is so great that it is at first ditJicult to realize that they 

 are not altogether different species. 



Mesodon alholabris, Say. — This our largest, and though not in 

 point of numbers, our commonest land snail, is, on account of its size 

 ^nd color, the one most frequently noticed by an ordinary observer. 

 Dead shells are often seen washed out by the rains from hillsides or 

 lying in strong contrast with the blackened soil in the woods where 

 tires have passed. Still, outside of a few localities I know of no place 

 whei'e an afternoon's diligent search would be I'ewarded with more than 

 a dozen living and mature specimens. The marl beds east of Hemlock 

 Lake can I find be always relied on to furnish this species in quantity. 

 It would be hard to imagine conditions more favorable, the marl not 

 only holding moisture well and producing grasses and mosses which, 

 in growth or decay, afford rich supplies of food, but also furnishing in 

 abundance, in what has once done duty for the same ])urpose, the very 

 material required for tho formation of shells. Aiiother place where I 

 lound M. albolahris common in the summer of 1883, is a ravine in Hull, 

 lying northward about a quai'ter of a mile from the house built and 

 formerly occupied by Mr. Lindsay Russell. This locality, however, 

 though visited often, afforded me very few shells during the past sea- 

 son, when ray best find was made in an open pastui-e near the magne- 

 «ian limestone quarries in Nepean. 



M. albolabris varies in greater diameter from 205 mm. to 30-25 

 Mim., representing in cubical capacity a ratio of 1 to 3|. These are ex- 

 tremes, and though numerous examples approaching either limit may 

 be found, the average size is nearer the maximum. The great majority 

 vary between 24 and 28 mm., and fifty shells measured give a mean 

 greater diameter of 26'2 mm. Very large or very small shells seem 

 confined to no pai-ticular locality, but occur indifferently in all. 



The bhell of this species althougli sometimes of a light greenish 

 •color, is usually of a beautiful russet. The lip, broad and white in old 

 specimens, is in the young comparatively narrow, and quite often of a 

 delicate rosy tint, which unfortunately soon fades in the cabinet. The 

 ■animal is generally of a ]iale grey color darkening towards the head. 



