390 COLLECTING LAND AND FRESH-WATER SHELLS. 



early days of spring, will reward the searcher abundantly. Kicli harvest may 

 also be frequently gathered by laying boards upon the grass or ground, wetting 

 them previously, unless immediately after a rain. On taking them up after a 

 night's exposure large numbers of shells will often be found attached to the un- 

 der surface. 



Fresh-water shells.— ^\i\\q searching for those species of land shells that are 

 found usually near water the collector will often have his attention drawn to 

 air-breathing molluscs that are properly designated aquatic mollusca. The 

 habits of some species of this class are such that by one unacquainted with 

 them they might be confounded with land shells. Many of these species have 

 a habit of crawling out of the water, remaining on the moist mud without in- 

 convenience. They will also sometimes be found on the stems and leaves ot 

 aquatic plants, or on other projecting substances several inches from the surface 

 of the water. In their habits as a class they are adapted to a wide range of con- 

 ditions, so that they will be found in lakes, ponds, rivers, canals, ditches, stagnant 

 pools, swamps, and small rivulets, though some species seem to be adapted to a 

 narrow range of conditions ; the class, however, has its representatives over the 

 whole continent. Though by far the greater number of species of molluscs be- 

 longing to this class prefer shallow water, feeding on the vegetation that abounds 

 in such stations, there are a few exceptions in which species are found adapted 

 to deep water, in which it is improbable they can reach the surface to respire 

 the air. The collector will find many species accessible to him along the margins 

 of water. Others will require the aid of a boat, especially such as arc found 

 feeding on the weeds in lakes and rivers. To discover some of the minute species 

 found under such circumstances it may sometimes be advantageous to gather 

 handsful of the weeds and gently lift them out of the water. If the operation 

 be rudely performed, the molluscs may be disturbed so as to detach themselves. 

 Many species will be found adhering to the grass-like plants that grow in 

 streams. Others adhere to the stems of flag and bullrush, and may be dis- 

 covered very readily by pulling up the plants by the roots, taking care to per- 

 form the operation gently and deliberately. Of analogous habits with some of 

 the above are certain small species found concealed under stones just below 

 low-water mark in rivers. They are sometimes also found adhering to larger 

 shells. This class embraces only small cup-like shells — "fresh-water limpets." 



Aside from the air-breathing aquatic molluscs, we have others whose respira- 

 tion is aquatic. The necessities of the respiration of the water -breathing mol- 

 luscs restricts them to a narrower range of circumstances than those to which 

 the air-breathing molluscs can conform. Hence they are not usually found in 

 stagnant waters— certainly not in waters of limited area, where impurities are 

 generated by decomposing substances. The largest shells of this class are found 

 in the swamps along the rivers of some of the southern States, and are objects 

 of interest on account of their habits as well as on account of their value in the 

 cabinet. In their season of active life they are found feeding on aquatic plants. 

 Inhabiting localities subject to drying they burrow in the mud as the water 

 diminishes. The collector will for convenience seek them when they are active. 

 Another class, smaller than that just mentioned, but affording a greater number 

 of species and varieties, is more widely distributed, being found not only in the 

 waters of the various States, but also in Canada. Tbey inhabit rivers, lakes, 

 ponds, and canals, and when circumstances favor their habits they will be found 

 most abundantly burrowing just beneath the surface of the soft mud near the 

 shores, where undoubtedly they are attracted by more abundant supplies of 

 food, and perhaps also by a more agreeable temperature. They will often be 

 found in the muddy banks of rivers in great numbers, congregated at the margin 

 of the water. In canals where conditions of food and temperature are very 

 favorable, they attain a more luxuriant development than in neighboring rivers. 

 Some localities are remarkable for affording varieties and monstrosities. Next 



