960 FRESH-WATER BIOLOGY 



and counties of the country should be compiled. Such local Hsts, 

 when the specimens are correctly determined, are of great value 

 and interest and are always acceptable contributions to scientific 

 hterature.^ 



The life history and habits of the different species form a subject 

 of great interest, and as yet but httle is known about them. Then, 

 too, very little is known of the internal anatomy of our species, 

 much less, indeed, than of the land mollusca. In all these lines 

 of work and study there is a fruitful and unreaped field of investi- 

 gation, which cannot fail to yield both pleasure and profit to the 

 student who will undertake to study the common forms of mollus- 

 can fife, which are to be found so abundantly in all parts of our 

 country. 



Collection and Preparation of Specimens 



Nearly every permanent body of water has its mollusks, varying 

 according to its character. Some species are found only in rapidly 

 flowing water, and others only in ponds and still water. Ditches 

 and other stagnant waters are usually good collecting ground for 

 Pisidia and other small species. The low places in the woods, 

 which dry up in the summer time, have a number of species that 

 are not found elsewhere, and which bury themselves in the mud 

 when the water disappears. Sand banks in rivers and lakes are 

 favorite resorts of many of the smaller species. The under side 

 of the Hly pads should be scrutinized, while the Ancyli should be 

 looked for on stones and dead clam shells. 



The distribution of the different species in all the states and 

 territories being of prime importance, the collector should always 

 bear in mind: 



First, that a dead shell is better than none at all; 



Second, that dead shells should not be taken, if five ones can 

 be had, and that careful search will usually discover them in the 

 immediate vicinity. 



Third, that all the species are extremely variable in their abun- 

 dance from year to year, and so it is a safe rule, "when you're 

 getting, to get a plenty." 



1 The writer will gladly aid students in the identification of their specimens without 

 charge. Address 45 Alfred St., Detroit, Mich. 



