138 THE CHICAGO ACADEMY OF SCIENCES. 



SUBCLASS ANISOPLEURA. 



Gastropoda in which the head and feet are bilaterally sym 

 metrical, but the visceral dome and mantle-flap, with all the 

 containing organs, have been subjected to a rotation, bringing 

 the anus from its posterior position to a point above the right 

 side of the animal's neck, thus causing the shell to incline to 

 the right side of the animal. As a result of this torsion the 

 organs of one side become atrophied. 



Superorder Euthyneura. 



Gastropoda anisopleura in which the nervous loop of the 

 viscera, being sunk below the body-wall, is not affected by the 

 torsion of the visceral hump, but remains straight. 



ORDER PULMONATA. 



Gastropoda with a well-developed foot and (usually) a 

 large, spiral shell, inoperculate (Amphibola excepted), capable 

 of containing the entire animal; some forms, however, are with- 

 out an external shell; the lungs are simple, being a pouch lined 

 with a network of respiratory vessels; respiratory orifice small; 

 sexes united in the same individual, but reciprocal union neces- 

 sary; the genital orifices may be contiguous or distant. The 

 lingual membrane is very variable, being in some forms short 

 and broad and in others long and narrow; the mouth is further 

 armed with one or more horny jaws. The Pulmonata are prin- 

 cipally terrestrial; but several large groups are aquatic, inhab- 

 iting fresh water, while some (Auriculidae) live in the neigh- 

 borhood of the sea and follow the ebb and flow of the tide. 



The pulmonates are typically vegetable feeders, although 

 some few genera are carnivorous (Circinnaria, Glandina). They 

 thrive best in warm, humid localities, and in desert countries 

 are stunted in size and few in number. 



The life history of a pulmonate gastropod is as follows: In 

 May or June they lay their eggs, to the number of forty or 

 more, in a moist locality, sheltered from the sun's rays, under 

 old leaves or by the side of logs or stones. After about twenty 

 or thirty days the young mollusk appears. It takes two or 

 three years for a snail to reach maturity. In October or No- 

 vember the snail ceases to become active and prepares to hiber- 

 nate. This it does by secreting a membrane and placing it 



