PHYSA. 483 



about the table, and will remain ont of water two or three clays 

 without injury. The shell is usually thickly coated with mud. 



Tliis species is distinguished from the young of L. elodes by the 

 depth of the suture, and the maturity of its aperture, whicli is also 

 proportionally larger. It is less elongated than L. desidiosa, its 

 suture is deeper, its aperture rather smaller, and the color is quite 

 different. 



Ranges from Nova Scotia to Georgia, and from Kansas to Lake 

 Superior. 



Ocniis PHYSA, Draparnacd. 1801. 



Tentacles slender, setaceous. Mantle covering part of the shell, 

 the margin fringed or digitate. Foot long, acuminate behind. 



Shell sinistral, oblong, thin, and polished ; spire acute ; aperture 

 oval, rounded anteriorly, not dilated ; inner lip spread over the last 

 whorl, simple in front ; outer lij) acute. 



Jaw single, superior, chevron-sliapcd. 



Lingual membrane with numerous transverse rows of teeth, ar- 

 ranged en chevron ; teeth long and slender with long lateral den- 

 ticles. 



This genus is widely distributed over the globe, and is numerous 

 in species in this country, where it extends more southerly than 

 Limneea. In its haliits it is more active than the other Lwinmdce, 

 both in walking and in gliding, shell downwards, on the surface of 

 the water. 



It will be seen in the generic descriptions of Phi/sa and Bulinvs 

 that the former name is restricted to those species having a digitated 

 mantle, and the latter applied only to those whose mantle is simple. 

 As Adanson founded his genus on a species having a simple mantle, 

 his name is retained for the last section, leaving Draparnaud's later 

 name for the first section. Thus any confusion of synonymy is 

 avoided. 



Pliysa heterostropha. 



Fig. 141. 



Shell ovate, smooth, yellowish-green ; whorls four, inflated, suture distinct, sur- 

 face reticulated. 



Lmna>a heterostropha, Say, Am. ed. Nich. Encyc. pi. i. fig. 6 (1817, 1818, 1819); Bix- 

 ney's ed. 46, pi. 69, fig. 6. 



