28 THE CHICAGO ACADEMY OF SCIENCES. 
with salts of various kinds. Many times, however, some hardy 
species survive in even brackish water; the effect of such a 
habitat is to dwarf and otherwise distort the shell. Some salt 
water species are known to inhabit both brackish and fresh water. 
The small bivalves, Pisidium and Spherium, prefer mountain 
pools, wet meadows, ponds and ditches. Anodonta prefers large 
ponds and slow moving streams, while the stouter Unio lives best 
on a hard, rocky bottom; in sandy bottoms they may be seen 
pushing themselves about quiterapidly. In pondsand sluggish 
streams the genera Physa, Limnza, Planorbis and Amnicola are 
found abundantly. Lily pads are good habitats for small mol- 
lusks, as are also the roots of trees and blades of swamp grass. 
6. CoLLtectinGc Outrit.—A fish basket makes a good collect- 
ing receptacle. A large basket is invaluable to carry the larger 
species like Unio and Anadonta. A dip net will be found useful] 
to dredge for those species which inhabit a muddy bottom. The 
small or minute species may be put in small vials, as mentioned 
for land shells. A flat bladed knife, or small trowel, and a pair 
of tweezers will complete the outfit. A scoop made of fine wire 
gauze will make a useful dredge to scoop the mud of shallow 
ponds and rivers. 
A small dredge, similar to those used in deep sea dredging, 
is of great value in collecting in the larger lakes. A strong man, 
or better, two men should row the boat and the one having 
charge of the dredge should be ever on the alert for obstructions 
on the bottom so that the dredge may not be damaged. A lead 
should be prepared with a hollow base in which to place some 
kind of grease to ascertain the character of the bottom, whether 
sandy or muddy, and should be attached to a stout line marked 
off in feet, to record the depth. These points should always be 
carefully noted with each haul, together with the distance 
from the shore. 
c. FavoraB_Le Loca.ities.—In (a) a number of good locali- 
ties have been given. Muskrat burrows are always good 
localities for the Unionide and the shells may frequently be 
found perfectly cleaned. The drift along the shore will yield a 
goodly number. As spoken of under land shells, so with fresh- 
water species, the eggs should be collected and preserved for 
study during development. These resemble drops of transparent 
jelly. For the preservation and study of the eggs, as well as 
small forms of adult mollusks, a small fish globe will serve as an 
excellent aquarium. Any jar of medium size will do equally as 
