THE NATURAL HISTORY SURVEY. 269 



sations regular, one hundred and forty to one hundred and 

 forty-six per minute. 

 Jaw: As usual. 



Raduta formula: ^+|+|+|-j-|+^+^( 2 2-i-22); cen- 

 tral tooth as usual; lateral teeth bicuspid, the inner cusp very 

 long and wide, bifid, the outer cusp smaller; marginal teeth long 

 and narrow, the distal end four-cuspid, and two small denticles 

 on the center of the outer margin ( Fig. 86). A second example 

 gave 15-1-15 teeth with six laterals. This latter was probably 

 an incomplete membrane, as several examinations gave the 

 result recorded above. 



Genitalia: Not examined. 



Distribution: New England to California, Canada to Geor- 

 gia, Texas and New Mexico. 



Geological distribution: Pleistocene; Loess. 



Habitat: Similar to that of desidiosa. It seems to prefer 

 the under side of boards, sticks and lily pads. 



\ 15 



Fig. 86. 



Radula of LIMN^A HUMILIS Say. (Original.) c, central tooth; 1, 

 first lateral; 15, ninth marginal. 



Remarks: As remarked under the last species, humilis is 

 closely related to desidiosa. It is always smaller (about one- 

 half), is rarely malleated, and the spire is shorter and more 

 conic and the aperture more rounded. This is one of our most 

 abundant species and may be found by the hundred in any 

 small pond or ditch, attached to submerged sticks, stones or 

 vegetation. It is, like all the Limnasids, very sociable, and is 

 always found in communities. L. desidiosa, caperata and palus- 

 tris are almost always found associated with the species. It is 

 as frequently out of water as in it, and this fact has led some 

 conchologists to identify it as Pomatiopsis. Not long ago a 

 number of specimens were given to the Academy by a gentle- 

 man who said they were found in wet moss, but not in the 

 water at all. He thought, from this fact, that they must cer- 

 tainly be a land mollusk. The writer has had this species 



