with a revision' of the Limnmdm of Authors. 355 



with a capnliform apex, from which concentric undulations ex- 

 tend to the margin. At the short, or posterior extremity, two 

 internal gutters or grooves (one on each side, the right hand one 

 being most prominent) extend to the margin ; somewhat resem- 

 bling the si phonal groove of Siphona/ria in appearance. By 

 their terminations the peristome is emarginated, especially on 

 the right side. 



Type Valenciennius anmdatus. Rousseau. 



Fossil in the Tertiaries of the Crimea, with Limncea, Planor- 

 bis, and other fresh-water shells. 



Group Piiysacea. 



Family PIIYSID.F. Dall. 



Foot pointed behind. Buccal plate (when present) without 



accessory laterals. Lateral teeth with comb-like, alternating 



with simple, cusps. Base of central tooth broad, bifid; cusp 



with several denticles. 



Sub-family Piiysin.e. 

 Genitalia on the left side. 



Genus Physa. Drap. 1801. 

 Mantle edge digitate or lobed. Buccal plate chevron-shaped, 

 or absent. Tentacles filiform, long. Shell sinistral. 



Sub-genus Physa. Drap. 1801. 

 Shell moderately elevated, ovate, outer lip and columella 

 simple. 



Type Physa fontinalis. Drap. 



Sub-genus Physella. Hald. IM:'. 

 Shell globose, spire short, aperture very wide, with a well- 

 marked fold on the columella. 

 Type PhyseUa gldbosa. Hald. 



Sub-genus CoxUitella. Dall. 

 Shell rounded, with transverse undulations or costre. 

 Type Costatella costata = Phyxa, <-ostnta. Newcomb. 



