THE MUSEUM. 



1 1 



not be damaged. A lead should be 

 prepared with a hollow base in which 

 to place some kind of grease to ascer- 

 tain 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 not- 

 ed with each haul, together with the 

 distance from the shore. 



Fresh-water shells may be found 

 almost everywhere; in ponds, ditches, 

 creeks, rivers and lakes. Any region 

 having a good water supply will sup- 

 port a fresh-water molluscan fauna. 

 There are some bodies of water, how- 

 ever, which are unsuited to molluscan 

 lift. When the bottom is made up of 

 coarse crystalline gravel few mollusks 

 will be found, but when there is a 

 large quantity of lime held in solution 

 in the water and when the bottom of 

 the stream or pond is muddy, the 

 chances are that a careful search will 

 result in the discovery of a numerous 

 and varied molluscan fauna. 



A rapid current is less favorable 

 than stiller water, although a few mol- 

 lusks (as the fresh-water melanians, 

 Pleurocera, Goniobasis, etc. ) are found 

 in streams; on rocks over which a 

 rapid current is flowing. When a 

 stream or pond has become more or 

 less filled with decaying vegetation, 

 the mollusks generally die off on ac- 

 count of the presence of carbonic acid 

 (carbon dioxide, C0 2 ) arising from 

 their decay. It is useless to expect to 

 find many mollusks under such con- 

 ditions. This not only affects the life 

 of the animal, but causes an excessive 

 erosion of the fhell, in the repair of 

 which the animal is weakened by the 

 enforced secretion of shelly matter. 



Those mollusks breathing by means 

 of gills will not voluntarialy inhabit a 

 body of water holding impalpable mud 

 in suspension, nor will they exist to 

 any extent in streams charged with 

 any Kinds of salts. Many times, how- 

 ever, 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 

 Sphaerinm, prefer mountain pools, wet 

 meadow ponds and ditches. Ano- 

 donta prefers large ponds and slow 

 moving streams, while the stouter 

 Unio lives best on a hard, rocky bot- 

 tom; in sandy bottoms they may be 

 seen pushing themselves about quite 

 rapidly. In ponds and sluggish 



streams the genera Ph)sa, Limnaea, 

 Planorbis and Amnicola are found 

 abundantly. Lily pads are good hab- 

 itats for small mollusks, as are also 

 the roots of trees and blades of swamp 

 grass. 



Besides the locations mentioned 

 above, the burrows of muskrats are 

 always good localities for Unios and 

 the shells may be found here perfectly 

 cleaned. The drift along the shore 

 will always be found to yield a large 

 number of perfect specimens. It is 

 frequently desirable to preserve a num- 

 ber of the shells of small bivalves 

 alive for study, and for this a medium- 

 sized fish globe is very useful. It will 

 be of great interest to the student to 

 study the living animal and record his 

 observations. Much is still unknown 

 concerning the habits of many of our 

 common fresh-water mollusks and 

 almost any student may add consider- 

 able information which will be of great 

 value. 



The preservation of the collections 

 obtained on each day's trip is of great 

 importance, for upon this depends the 

 appearance and value of the collector's 

 cabinet. When the specimens are 

 collected they are covered with mud 

 and growths of various kinds, and 

 must be thoroughly cleaned. In the 

 case of fresh- water shells, they should 

 first be washed clean of mud, etc. ; 

 this may be removed easier by the aid 

 of a tooth-brush. The soft parts may 

 be removed by putting the animal for 

 a few seconds in boiling water. If 

 they are first placed in lukewarm wa- 

 ter for a few minutes and then tran - 



