[11] INSTRUCTIONS FOE COLLECTING MOLLUSKS DALL. 



to fatten upon them. In America we have no species of snail which 

 lives in such numbers among the herbage as do the British forms 

 alluded to. Birds usually destroy the shells of the snails upon which 

 they feed, and so are injurious to collectors. But Glandina, a carnivo- 

 rous snail common in the Southern States, swallows the smaller Helices 

 whole and digests the soft parts at leisure, as the walrus does with sea 

 snails. As many as a dozen specimens of Polygyra have been extracted 

 from the gullet of a single Glandina. Many of the snails of the type 

 of Zonites are carnivorous, and the collector must beware of put- 

 ting species he would keep alive into a box or fernery with such forms 

 as Selenites concava. The latter will make short work of them, extend- 

 ing its slender body far into the whorls of its defenseless prey and eat- 

 ing them, all alive, voraciously. A siugle Selenites will clean out a 

 dozen Helices of its own size in a single night. A Floridian bird of 

 prey, the everglade kite {Bostrhamus sociabilis), is said to have a special 

 fondness for Amj)ullaria, and the curve of its beak and the formation 

 of its claws are specially adapted for preying upon them and extracting 

 the body of the snail from behind its protecting operculum. Certain 

 millipedes of the genus Julus are often found feasting upon slugs and 

 snails, but whether they attack specimens in good health is not posi- 

 tively determined. 



The treatment of specimens collected, including methods of cleaning 

 and preservation of the soft parts, ^ill be discussed later. 



FEESH-WATER SPECIES. 



The moUuscan fauna of fresh waters includes both Gastropods and 

 Pelecypods. All regions having permanent bodies of fresh water, 

 whether lakes, x)onds, rivers, brooks, or even springs, present a certain 

 number of species, which, however, varies greatly with the more or 

 less favorable nature of the environment. 



HABITAT AND STATION. 



As lime forms the chief comjDonent in shell, waters containing an 

 abundant supiDly of this mineral are more favorable for the multiplication 

 of shell-bearing animals than those which contain but little lime. As 

 the development of molluscan embryos is more rapid and effective in 

 warm than in cold water, a temperate or warm climate favors the mul- 

 tiplication of individuals. The character of the bottom influences the 

 welfare of mollusks ; a coarse crystalline gravel, more or less disturbed 

 by a rapid current, is distinctly less adapted to them than softer and 

 less gritty sands, mud, or even solid rock, over which the water flows 

 more gently. The food supply is, of course, of great importance and 

 the presence of algtE or other plants m abundance, by promoting the 

 multiplication of the microscopic organisms upon which many mollusks 

 feed, is indirectly advantageous to those species which may not feed on 

 the plants themselves. 



