FIELD BOOK OF PONDS AND STREAMS 



"^ Fig. 247 — Shell of LymncBa columella, whose body 

 whorl is three times as large as its spire. 



Lymnaea columella (Pseudosuccinea). — The shell (Fig. 247) 

 is greenish or yellowish, with 4 whorls the last of which forms 

 nearly the whole shell; the lines of growth are very heavy. 

 The body aperture is oval, expanded at the lower part. 

 Length of shell, three-quarters of an inch. 



Occurrence. — Like L. stagnalis this species lives in quiet 

 water on lily pads, among cat -tails; it is rarely in running 

 water. Generally distributed throughout the United States. 

 Baker (Bibliography, p. 421) gives this species as Pseudosuc- 

 cinea columella. 



Pouch-snails, tadpole snails, Family Physidae. — The shells 

 of Physidce are left-handed (Fig. 240), with a very large lower 

 coil, and the spires are sharp-pointed but short. The animal 

 has a narrow foot, pointed behind, and finger-like outgrowths 

 along the edge of its mantle which are very characteristic. 

 These are active snails which are extremely variable in color 

 and shape and ver>^ difficult to identify. 



Occurrence. — ]Most of them are found in the United States 

 and Canada. 



Fig. 248. — Tadpole snail, Physa gyrina {Phy sella) : 

 I, animal showing the slender pointed foot (after 

 Baker) ; 2, shell. 



Tadpole snail, Physa gjrma. (Physella gyrina of Baker). — 



The shell is thickened, heavy looking, with 5 or 6 coils. The 

 body aperture is loop-shaped, the outer lip, (Fig. 248) is apt 



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