LIMNEA JUGULARIS. 17 



GEOGRAPHICAL DISTRIBUTION. Lakes in New 

 York, Michigan, North-west Territory, (fig. 2.) 

 and Lewis's river, Oregon, (fig. 1.) 



OBSERVATIONS. 



The shell of this species bears a very close 

 resemblance to that of L. stagnalis, but may 

 be distinguished by the want of the prominent 

 shoulder to the whirls, which is so conspicuous 

 in that species. A single monstrous individual, 

 presented to Academy's collection by Mr. 

 Nuttall, has, however, a well developed shoulder. 

 The surface of Stagnalis has a tendency to 

 form facets, which is not the case with Jugu- 

 laris; nor has it the spiral striae quite as evi- 

 dent; a character still better developed in L. 

 appressa. The revolution of the edge of the 

 columella leaves a conical open axis, of about 

 equal size in both species (but narrower in L. 

 appressa) which admits of a view far into the 

 shell. Both species agree remarkably well in 

 the colour, texture, and translucency of the 

 shells. 



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