THE NATURAL HISTORY SURVEY. 267 
long, reaching below the lower margin of the base of attach- 
ment, the side cusp smaller; the eight to sixteen laterals are 
tricuspid, the inner cusp very small; these may be called inter- 
mediate marginals; marginals at first (seventeen to twenty) 
modified laterals, with a long, bifid inner cusp and two very 
short outer cusps; balance of marginals long and narrow, ser- 
rated, generally three short cusps at the distal end and two 
short cusps at the outer side; these latter disappear toward the 
outer part of the membrane (28-45); all have cutting points, 
especially well developed on the laterals and first marginals 
(Fig. 85). 
Genttaia: Not examined. 
Distribution: New England to Iowa, Canada, Manitoba 
and California, south to Virginia, Kentucky and New Mexico. 
7-20 
17 
45-46 A427 
Fig. 85. 
Radula of LIMN#A DESIDIOSA Say. (Original.) c, central tooth; 
1, first lateral; 8, lateral tooth; 17-20, modified marginals; 21-45, various 
types of marginals. 
£4 
Geological distribution : Pleistocene; Loess. 
Habitat: In small bodies of water, clinging to submerged 
stones and sticks. It occasionally inhabits the larger rivers. 
Prefers still water, and has been dredged in Lake Superior at 
a depth of 8 to 13 fathoms. 
Remarks: This species is subject to some little variations 
and numerous names have been given to these forms.* In the 
main, however, it may be recognized by its long, pointed apex, 
*It is evident from a study of present material and the original figures and descrip- 
tions, that several other species will have to become synonyms of desidiosa; L. obrussa Say 
and L. fusiformis Lea may be considered doubtful species. 
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