Baker—Molluscan Fauna of Tomahawk Lake, Wisconsin. 227 
TAXONOMY. 
An analysis of the fifty-three species of mollusks recorded 
in the systematic catalog reveals several interesting facts. 
It is at once seen that the Gastropods (32) exceed the Pele- 
cypods (21) almost three to two. The Gastropods divide 
naturally into three groups as follows: 
Prosobranchiates . 2 
Land pulmonates . 9 
Presh-water pulmonates.21 
The large preponderance of the fresh-water pulmonates is 
noteworthy. A large portion of this excess is divided be- 
tween Planorbis and Lymna, each with seven and eight spe¬ 
cies* respectively. This is to be expected, however, as these 
genera are typically northern in distribution, the number of 
species increasing largely in the boreal zone. Of the naiads, 
the Wisconsin River and its tributaries produced nine species 
while the lake produced but three, which is in accord with the 
well known fact that this family is typically an inhabitant of 
rivers. 
The mollusk fauna of this region includes two elements; 
first, the species which are widely distributed throughout the 
greater portion of North America, and, second, those species 
which are purely boreal in distribution. These two elements 
may be compared in the subjoined tables. 
Widely Distributed Species. 
Lampsilis luteola. 
Anodonta marginata. 
implicata. 
grandis footiana. 
Symphynota costata. 
compressa. 
ventricosa. 
ligamentina. 
recta. 
Strophitus edentulus. 
In this analysis varieties are treated as species for convenience. 
