ii8 



THE MUSEUM. 



found, congregated in hundreds, under 

 stray fragments of boards, bits of wood, 

 etc., in wet grass lands, ihat are moist 

 during a considerable portion of the 

 year. Always be on the alert and ex- 

 amine every likely place, and your ef- 

 forts will usually be well rewarded. 



Fresh Water Shells. — Among the 

 smaller fresh water shells, one is sure 

 to find some air-breathing molluscs 

 that are called aquatic niolltisca. One 

 might think they were land shells, as 

 many species have a habit of crawling 

 out of the water and remaining on the 

 moist mud without inconvenience. 

 They are also found on the stems and 

 leaves of aquatic plants. In their hab- 

 its they adopt a wide range of condi- 

 tions and may be found in lakes, 

 ponds, rivers, canals, ditches, stagnant 

 pools, swamps and small rivulets. By 

 far the greater number of species of this 

 character prefer shallow water, and 

 may be found usually along the mar- 

 gins. By pulling up the stems of 

 fiags or bullrush, many species may be 

 discovered. A class of minute cup- 

 like shells, ''Fresh Water 'Limpets " 

 are frequently found adhering to the 

 sides of other shells, under the mar- 

 gins of stones, etc. Aside from the 

 air-breathing aquatic mollusca, we 

 have some whose respiration is aquatic. 

 These are not usually found in stag- 

 nant waters. The largest shells of 

 this class are found in swamps along 

 the rivers of some of the southern 

 states. In their season of active life 

 they are found feeding on aquatic 

 plants, but where the water dries up, 

 they burrow in the mud. It is best to 

 collect them while active. Another 

 class, smaller than those just mention- 

 ed, but affording a greater number of 

 species and varieties, is found all over 

 North America. They inhabit rivers, 

 lakes, ponds and canals, and when cir- 

 cumstances favor their habits will be 

 found most abundantly, burrowing 

 just beneath the soft mud near the 

 shores, usually at the ntargin of the 

 water. They frequently acquire a more 

 luxuriant growtfi in canals than in 



neighboring rivers. Next to this class 

 in size is one that embraces a large 

 number of species included in several 

 genera and sub-genera. The shells 

 vary in form from a slender turret to 

 globular, variously colored, and fre- 

 quently ornamented with tubercles, 

 ridges and carinations. With few ex- 

 ceptions, they are found in rivers and 

 perennial streajiis. Some of these 

 molluscs prefer viuddy sloping river 

 hanks, where they crawl on the sur- 

 face of the mud. Others prefer the 

 rapid current among the rocky portions, 

 where they adhere to the surface of 

 the rocks. The habits of the majority 

 of this class, however, are such as to 

 bring them to the shallower portions of 

 the water they inhabit, and they can 

 often be reached from the shore with 

 the hands. By gradual transitions, 

 these genera with their numerous spec- 

 ies are followed by other and smaller 

 genera, some of which have a compar- 

 atively limited range and others are 

 widely distributed over the whole coun- 

 try. Nearly all of them have habits in 

 some respects similar to the last pre- 

 ceding class, and will be found on the 

 muddy bottoms of shallow portions of 

 rivers, lakes, etc., feeding on aquatic 

 plants. 



Fresh- water Bivalve Shells. — Might 

 be divided into two classes, small and 

 large. The small forms, none of 

 which are ever over a half an inch 

 long, inhabit nearly every perennial 

 stream having a muddy bottom. Also 

 lounA'm stagnant waters, lakes, ponds, 

 canals, and indeed, in every station 

 fitted for mollusc life. They all bur- 

 row just beneath the surface of the 

 vuid, and are found in greatest abund- 

 ance near the margin of the water, or 

 where there is but little depth. Some 

 of the species are extremely frail, and 

 some are very minute. The larger bi- 

 valve shells, called Fresh Water Mus- 

 sels or Fresh Water Clams, embrace 

 a large number of genera and sub-gen- 

 era. No country in the world pro- 

 duces as great a variety of forms as the 

 United States. In the north-eastern 



