THE NATURAL HISTORY SURVEY. 269 
sations regular, one hundred and forty to one hundred and 
forty-six per minute. 
Jaw: As usual. 
Radula formula: +2+4+8+1+4+4+4+}2 (22—1—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). Asecond example 
gave IS-I-15 teeth with six laterals. This latter was probably 
an incomplete membrane, as several examinations gave the 
result recorded above. 
Genitaha: Not examined. 
Distribution: New England to California, Canada to Geor- 
gia, Texas and New Mexico. 
Geological distribution: Pleistocene; Loess. 
Habitat: Similar to that of destdiosa. It seems to prefer 
the under side of boards, sticks and lily pads. 
1 
Fig. 86, 
Radula of LIMN&A HUMILIS Say. (Original.) c, central tooth; 1, 
first lateral; 15, ninth marginal. 
1S 
Remarks: As remarked under the last species, humilis is 
closely related to des:diosa. It is always smaller (about one- 
half), is xavely 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 Limnzids, very sociable, and is 
always found in communities. JL. destdiosa, caperata and palus- 
tris are almost always found associated with the species. It is 
as frequently out of water as init, and this fact has led some 
conchologists to identify it as Pomatopsis. 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 
