with a revision of thè Limnoeidm of Authors. 355 
with a capuliform apex, from which concentric undulations ex- 
tend to tlie margin. At thè short, or posterior extremity, two 
internai gntters or grooves (one on eachside, thè right hand one 
being most proininent) extend to thè margin ; somewhat resem- 
bling thè siphonal groove of Siphonaria in appearance. By 
their terminations thè peristome is emai’ginated, especially on 
thè right side. 
Type V alenciennius annulatus. Rousseau. 
Fossil in thè Tertiaries of thè Crimea, with Limncea, Planar- 
òis, and other fresh-water shells. 
Group Physacea. 
Family PHYSIDyE. Dall. 
Foot pointed behind. Buccal piate (when present) without 
accessory laterals. Faterai teeth with comb-like, alternating 
with simple, cusps. Base of centrai tooth broad, bifid ; cusp 
with several dentieles. 
Sub-family Physin^. 
Genitalia on thè left side. 
Genus Physa. Drap. 1801. 
Mantle edge digitate or lobed. Buccal piate chevron-shaped, 
or absent. Tentacles tìliform, long. Shell sinistrai. 
Sub-genus Physa. Drap. 1801. 
Shell moderately elevated, ovate, outer lip^ and columella 
simple. 
Type Physa fontinalis. Drap. 
Sub-genus Physella. Hald. 1842. 
Shell globose, spire short, aperture very wide, wdth a well- 
marked fold on thè columella. 
Type Physella globosa. Hald. 
Sub-genus Costatella. Dall. 
Shell rounded, with transverse undulations or coste. 
Type Costatella costata = Physa costata. Hewcomb. 
