A SYNOPSIS OF THB: CLASSIFICATION OF THE FRESH-WATER 

 MOLLUSCA OF NORTH AMERICA, NORTH OF MEXICO. 



Class GASTROPODA. 



Subclass EUTHYNEURA. 



Order PULMONATA. 



Suborder BASOMMATOPHORA. 



Superfamily LIMNOPHILA. 



The North American Limnophilce are in the main inhabitants of fresh 

 water, but are occasionally found in slightly brackish water along the sea 

 coast. The epidermis is smooth; the contractile tentacles are flattened or 

 cyhndrical; the eyes are placed on the inner bases of the tentacles. The 

 genital orifices are separated, the male orifice is near the tentacle, the female 

 at the base of the neck, near the respiratory orifice. The jaw is simple or 

 composed of three pieces. The radula has numerous rows of small teeth. 



Key to the families of Limnophila. 



I. Shell spiral, dextral, spire more or less elongated Lymnceidce. 



II. Shell discoidal, with the columellar margin simple. 



not dilated Planorhid^e. 



III. Shell spiral, sinistral Physidce. 



IV. Shell patelliform or spiral, dextral, neritoid or planorboid 



with the columellar margin broadly dilated Ancylidce. 



Family LYMN^ID^. 



Shell spiral, dextral, spire usually elongated and acute, but in some groups 

 small and depressed. 



Animal dextral. Head with a broad, short muzzle dilated at the end. 

 Foot rounded behind. Tentacles flattened. 



Jaw composed of three plates, a large one in the center, with two small, 

 narrow laterals. Radula broad ; central tooth small, simple or bicuspid, the 

 laterals bi- or tricuspid. The marginals- bi-, tri-, or multicuspid or serriform. 



Genus LYMN^EA Lamarck, 1799. 



Shell spiral, dextral, thin, unicolor or occasionally with longitudinal 

 stripes ; spire usually acute ; aperture large, oval, rounded below, extremities 

 united by a thin parietal callus ; columella more or less twisted or plicate ; 

 lip thin, sometimes with an internal thickening or varix. Animal dextral: 

 head large ; tentacles flattened, triangular ; eyes sessile on the inner bases of 

 the tentacles. 



