a turtle or snake egg. Many marine snails have a complicated infancy in- 

 volving a ciliated, free-swimming stage called a veliger. Land and fresh-water 

 snails have a more variable environment with which to contend and have 

 telescoped their developmental stages into a brief period while they are still 

 within the egg or else have omitted the ancestral recapitulations entirely. 



Snails are seldom of much direct economic importance to man. In Europe 

 some of the larger snails are used for food. In America their use is indirect, 

 since most of us prefer to eat the fish and birds that feed upon the snails. The 

 diet of a number of the fishes, such as the pumpkinseed sunfish and some of the 

 suckers, consists of twenty-five per cent or more of mollusks. Occasionally land 

 snails, especially slugs, are destructive to tender garden plants. One genus 

 of snails, Lymnaea, serves as an intermediate host for the sheep liver fluke, a 

 parasite that frequently causes great losses. 



Snail shells are easily preserved. A shell in which the occupant has died 

 and decayed often loses its markings and luster and is regarded as a "dead 

 shell", of little value to collectors. During and after damp warm weather on 

 land, and at almost any time in the water, live snails can be obtained. Logs 

 or boards which have been long submerged, and stems of water plants, usually 

 harbor snails. On land, snails arc usually found under loose bark or decaying 

 logs or stumps. Live snails, unless very small, are usually killed by dropping 

 them for a moment or two into boiling water. The animal can then be gently 

 "unscrewed" from its shell with the aid of a pin. If an operculum is present, 

 it should be removed, dried flat between two pieces of glass, and placed inside 

 the shell, the aperture of which is then plugge*d with cotton-wool. Even if 

 the operculum is lost, the cotton plugs should be used in all operculate shells 

 as an indication. Inoperculate shells are left open. A number should be writ- 

 ten on the shell with India ink to correspond to the number of the label or 

 written record, on which the place and date of collection and other useful 

 data are given. 



Minute shells may be dropped into alcohol for a day or two and then 

 dried, as the occupants will then mummify and not spoil the shells. Small or 

 delicate shells are usually kept in glass vials, with cotton below and cotton 

 plugs above, or else are put, together with their labels, into gelatin capsules, 

 which are available at druggists. The number and the record of date and 

 locality should always be most carefully recorded, as a collection without such 

 data has lost much of its scientific value. 



There are two families of bivalve mollusks found over most of the United 

 States. The members of the larger of these, the Unionidae, are the common 

 clams or fresh-water mussels. They have nacreous or mother-of-pearl linings 

 to the shells and usually attain an adult length of more than an inch. The other 

 family, the Sphaeriidae, are commonly called "finger-nail shells". They are 

 usually less than an inch long and have dull, instead of iridescent, linings. 



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