CLASSES, ORDERS, ETC. 69 



shallow ; mouth oval-lanceolate. Length -| to |ths inch. Ponds, 

 ditches, and slow-running streams. More or less local. 



P. (Aplecta] hypnorum^ 



(b) Shell oval, thin, glossy, semi-transparent, pale greyish-horn 

 coloured ; whorls four to five, tumid, the last one occupying |ths or 

 ^ths of the shell ; suture deep ; mouth oblong and wider and larger 

 in proportion than in P. hypnorum. Length j inch. Running 

 brooks, canals, ditches, and sluggish rivers. Common. 



P. fontinalis 



(c) Shell an elongated ovoid, ventricose, glossy, finely striated 

 longitudinally, light horny or whitish in colour ; whorls three, 

 the last one f ths of the total height of the shell ; suture moderately 

 deep ; apex sharp ; mouth obliquely and narrowly oval, acute 

 above. Height grd to frds inch. In one of the lily tanks in 

 Kew Gardens. Imported. P. acuta. 



8. Limnsea. Shell oval, thin, translucent ; mouth oblong ; 

 columella with an oblique plait ; non-operculated. Animal with 

 two short triangular tentacles bearing the eyes at their base ; foot 

 oval. 



(a) Shell oval, globular, amber or yellowish-horn coloured, thin, 

 transparent ; whorls three to four, inflated, the last one forming 

 nearly the whole of the shell; spire slightly produced; suture 

 rather deep ; mouth oval. Mantle partly covering the shell. 

 Length J inch. Ditches, ponds, and lakes. Very local. 



L. glutinosa* 1 



(b} Shell ovate, thin, fragile, glossy, pale amber- coloured, glossy, 

 whorls three to four, convex, the body whorl very large; spire 

 sunk within the last whorl; suture shallow; mouth pyriform, 

 large. Length 5^ lines. In a small alpine lake on Cromaglaun 

 Mountain, Killarney, Ireland. L. involuta. 



(c) Shell oval, last whorl swollen," thin, glossy, yellowish-horn 



29 v. cuprella, copper-coloured, whorls six, convex, the last one far exceeding 

 in size the rest put together, mouth oval, contracted above ; v. major ; larger, 

 more coloured, height 10 to 13 mm; m. decollatum, spire decollated. 



30 v. albina, milk-white ; v. oblonga, spire considerably produced ; v. inflata, 

 larger, more ventricose ; v. ctirta, spire extremely short ; m. dextrorsum, spire 

 dextral. 



31 v. mucronala, not quite so globular, spire more produced. 



