Sterki: Collecting Sph.^riid.e, 483 



late summer and fall. It is desirable that accessible places be visited 

 at various seasons, especially for Musculium, of which at least a large 

 part become full-grown, and then die in early summer to midsummer, 

 the time when also most of the LymncBa, Planorbis, Physa, etc., attain 

 maturity. A large percentage of Musculia now in collections are 

 immature, and it appears that of some forms only young and half- 

 grown specimens are known. In some instances observations have 

 been made and series of specimens at successive stages of growth 

 were secured by collecting at the same places every few weeks from 

 spring to midsummer, or fall. It will also be interesting to compare 

 observations made in this respect in the North and in the South. 



Drift. 



Fine drift on the shores and beaches of lakes, accumulated in heaps 

 and rows, or thinly scattered, almost always contains shells. Though 

 generally more or less bleached and waterworn they are well worth 

 taking. From drift-heaps good quantities should be taken along. 

 Scattered specimens on the beach may be swept on to a piece of card- 

 board or tin with a feather. 



Drift accumulated along rivers, creeks, or ravines after floods and 

 heavy rains, from a handful or less to large heaps, are always worth 

 taking. A sieve, if at hand, will help in separating the coarser material 

 from the finer. Most of the shells it contains are generally of small 

 land-snails, often thousands of them, but some aquatic mollusks are 

 usually also found. 



Fossils. 



Fossil specimens should be collected wherever possible from the 

 fresh-water deposits of the Tertiaries and older formations, from which 

 very few so far are extant. Valuable material should be found 

 especially in the Western States. It is barely necessary to say that 

 they should be handled very carefully, since the shells are thin and 

 tragile, and that not only the locality should be noted, but also the 

 formation and stratum. 



Marl deposits, in a number of states, have been more or less explored, 

 and many of them are wonderfully rich in shells of the Sphseriidae 

 and Gastropods. Generally the marl is so soft that the shells can 

 be washed out of it with proper care, and thus it is possible to take 

 good quantities along to be worked up at home. 



