CH. VII] SNAILS AND SLUGS 239 



dilatatus Gould, T y, whorls 2, angulated, aperture very large 



and squarish, umbilicus small, deep : found only in canals near 



Manchester ; probably introduced by shipping. 

 crista (L.), ^y, whorls 3, last whorl rather large, small imbricated 



ridge, aperture oval, umbilicus large. 

 spirorbis (L.), ^", whorls 5 or 6, one side concave, the other flat ; 



keel frequently blunt, aperture roundish, often ribbed with 



white, umbilicus wide and shallow. 

 vortex (L.), f", whorls 6 to 8, upper side concave, under side flat, 



keel on lower margin and always well marked ; aperture 



rhombic ; umbilicus large, shallow, 

 genus Segmentina Fleming, shell flattened, last whorl embracing 



the rest, keeled ; aperture transverse, angular ; interior with 



lamellar, teeth grouped in threes. 

 nitida (Mull.) = Planorbis lineatus (Walker), ^", whorls 4. 



Family AURICULID^E. Shell spiral, spire short, body whorl large, 



aperture toothed, tentacles two, eyes at base, 

 genus Carychium Mull., tentacles relatively large, cylindrical ; 



eyes below and behind base of tentacles. 

 minimum Mull., ^5", shell transparent, oblong, finely striated 



transversely, aperture oval, toothed, margin thickened; 



whorls 5^. In damp places, under rotten wood and dead leaves, 

 genus Phytia Gray, tentacles cylindrical, swollen at apex; foot 



not divided. 

 myosotis (Drap.). 

 genus Ovatella Bivona, tentacles short, compressed ; foot divided 



by a transverse groove. 

 bidentata (Montagu). 



Sub-order PULMONATA. 



(Stylommatophora. Eyes on summit of two hollow tentacles. 



Almost exclusively terrestrial.) 

 Family ZONITIDJE. 



germs Vitrina Drap., pellucida (Mull.), J", shell greenish, sub- 

 globular, thin, vitreous, whorls few, increasing rapidly, no 

 umbilicus, aperture large, ear-shaped, animal incapable of 

 retreating entirely within shell. In shady and moist places, 

 under stones and moss. 



