106 MALACOZOA. GASTEROPODA. PULMOBRANCHIATA. 



right side, in the form of a groove on the collar, and 

 capable of being covered by a fleshy appendage by which 

 it is margined beneath; intestinal aperture near the 

 pulmonary ; genital organs distant, the orifice of the 

 male under the right tentaculum, that of the female 

 organ at the pulmonary aperture. 



Shell oval or oblong, thin, fragile, dextral, with a 

 tapering, pointed spire ; the aperture longer than wide, 

 oval, sharp-edged ; the columella with an oblique plait. 



They inhabit still water, brooks, rivers, and ditches. 

 In a state of repose, they adhere to stones or plants by 

 their foot. They crawl slowly, can advance along the 

 surface of the water, in a reversed position, are capable 

 of remaining long under water, and in drought sink 

 partiaUy into the mud, or creep into shady places. 



Some of the species vary so much in form, that authors 

 are not agreed as to what ought to be considered as 

 varieties. 



1. Limnceus p&reger. Wandering Mud-Shell. 



Shell ovate, thin, horny, semitransparent, of four trans- 

 versely striated, convex turns, the last very large ; the spire 

 very short> acute ; the aperture ovate, acute behind, with the 

 inner lip reflexed on the columella, leaving a concealed nar- 

 row groove from the umbilicus ; the colour varying from pale 

 greyish-yellow to umber or dark reddish-brown. Length from 

 half an inch to an inch, breadth generally two-thirds of the 

 length. 



Helix limosa. Linn. Syst. Nat. Buccinum peregrum. Drap. 

 Verm. Terr. et. Fluv. ii. 130. Limnea limosa. Flem. Brit. Anim. 

 274. Limnaeus pereger. Gray's Turton. 233. 



The principal varieties which this species presents, are the 

 following: 



A. Limnceus pereger ovdtus. Ovate Mud-Shell. 



Shell ovato-elliptical, ventricose, very thin, brittle, semi- 

 transparent, glossy ; with the spire extremely short ; the aper- 

 ture obliquely extended, oval, acute behind, four-fifths of the 

 whole length ; the tip often eroded ; the last turn oblique, 

 finely but distinctly striate transversely ; the colour pale greenish- 

 yellow. Length ten-twelfths of an inch, breadth seven-twelfths. 



