CONCHOLOGY. 117 



Shell often sinistral, oval, oblong, or globular, perfectly 

 smooth ; aperture oval, contracted posteriorly ; the right 

 edge sharp, advanced above the plane of the left edge ; col- 

 umella twisting obliquely, and enlarging to join itself to the 

 anterior part of the columellar margin. 



Physa castanea. Physa hypnorum. 



P. fontinalis. P. subopaca. 



P. fontinalis. The fountain Physa. PI. 20, fig. 2. 

 Volutions reversed, oval, ventricose, pellucid, horn-colour- 

 ed ; spire short and acute. 



3. Lymnsea. Eleven species. 

 Shell aquatic, oval, turreted or conical, thin, smooth, spire 

 pointed ; aperture oval, entire ; edges disunited, the left 

 with a very oblique plait at the point of junction of the col- 

 umella with the rest of the margin. 



Lymnsea stagnalis. Lymnaea auricularia. 



L. palustris. L. ovata. 



L. Virginiana. L. peregra. 



L. luteola. L. intermedia. 



L. acuminata. L. leucostoma. 



L. minuta. 



L. stagnalis. The pond Lymnasa. PI. 20, fig. 1. 

 Ovate, ventricose ; spire subulate and very acute ; aper- 

 ture large and ovate ; horn coloured. 



L. leucostoma. The shining Lymnasa. 



Species sub-turreted, with the right edge thickened. 



FAMILY IX. 



Melanides. Three genera. 



1. Melania. Sixteen species. 

 Likewise taken from the Helix of Linnaeus. 

 Shell fluviatile, covered with epidermis, oval, oblong ; spire 

 slightly pointed, more or less turreted ; the margin of the 



