THE AQUARIUM, JULY, 1894. 



115 



WHERE SNAILS ABOUND. 



For fresh water species various resorts 

 are to be searched. Go to the torrents 

 with rocky bottoms for the pah;dinas 

 and periwinkles (Melania) ; to quiet 

 brooks for physas and coilshells ; to 

 stagnant pools in the wet ooze and the 

 reeking swamps for limneas. We know 

 no better place in the world for pond 

 snails than the tule marshes of the 

 Pacific slope, where hundreds of the 

 great graceful Limnea stacpialis lie 

 among the rotting vegetation, or float 

 upside down at the surface of the still 

 water. But some of the fresh water 

 mollusks remain most of the time at 

 the bottom, coming to the surface only 

 to breathe now and then, and to get 

 their shells it is necessary to use a sieve- 

 bottomed dipper, or some sort of dredge. 

 When the water becomes low they bury 

 themselves in the mud ; it is therefore 

 always profitable, late in the summer, 

 to rake out the bottom of mud-holes 

 where the water has entirely disap- 

 peared. Another plan is to gently pull 

 up the water weeds by the roots and 

 cleanse them in a basin of water. You 

 will thus secure many very small 

 species. Experience will quickly teach 

 the collector where he may expect to 

 find this and that kind, and that some 

 caution and much sharpness of observa- 

 tion are necessary, since some species 

 by their naturally dead tints, and others 

 by a coating of mud, assimilate them- 

 selves so nearly to their surroundings 

 as easily to be overlooked. 



The shell is increased raj^idly for the 

 first two or three years, and the delicate 

 lines of increment, parallel with the 

 outlines of the aperture, are readily 

 visible on all the larger specimens. 

 Various other signs indicate youth or 

 adult asre in the shell. 



Mollusks prosper best, coeteris ]^ari- 

 bus, in a broken landscape, with plenty 

 of lime in the soil. The reason, no 

 doubt, why the West India Islands, 

 the Cumberland Mountains and similar 

 regions are so peculiarly rich in shells 

 of every sort, is that a ravine-cut sur- 

 face and a Avide area of limestone rocks 

 characterize those districts ; on the 

 other hand, it is not surprising that we 

 found nine-tenths of the Rocky Moun- 

 tain species to be minute, since the 

 geology is represented by sandstone and 

 volcanic rocks. Hot springs are very 

 likely to be inhabited by mollusks, even 

 when the temperature exceeds 100 de- 

 grees Fahrenheit, and the waters are 

 very strongly impregnated with mineral 

 salts. 



Snails are mainly vegetarians, and all 

 their mouth parts and digestive organs 

 are fitted for this diet. Just below the 

 lower tentacles is the mouth, having 

 on the upper lip a crescent-shaped jaw 

 of horny texture, with a knife-like, or 

 sometimes saw-like, cutting edge. The 

 lower lip has nothing of this kind, but in 

 precisely the same attitude as our tongue 

 is arranged a lingual membrane, long, 

 narrow and cartilaginous, which may 

 be brought up against the cutting edge 

 of the upper jaw. This "tongue" is 

 studded with rows of infinitesimal silic- 

 ious ''teeth," eleven thousand of which 

 are possessed by our common white- 

 lipped helix, although its ribbon is not a 

 quarter of an inch long. All these sharp 

 denticles point backward so that the 

 tongue acts not only as a rasp, but 

 takes a firm hold upon the food. On 

 holding the more transparent snails up 

 to the light it is easy to see how they 

 eat, and you can hear a nipping noise 

 as the semi-circular piece is bitten out of 

 the leaf. Their voracity often causes 

 immense devastation, particularly in 



