XVI ANALYTICAL KEY. 



Carrying a horny narrow-whorled shell. Lower tentacles short P UP A. 



Shell rather large, of eight to nine whorls, aperture seven- toothed — secale. 



Shell small, of seven glossy whorls, aperture toothless or one-toothed — muscorum. 



Shell very small, of six rather swollen whorls, aperture one-toothed — cylindracea. 



Shell small, of six narrow whorls, aperture triangular, five-toothed — Anglica. 



Carrying a minute shell. No lower tentacles. Inhabiting wet places VERTIGO. 



Shell tumidly cylindrical, of five whorls, aperture six to nine-toothed — antivertigo. 



Shell tumidly ovate, of five whorls, aperture two to four-toothed — Moulinsiana. 



Shell ovately cylindrical, of five whorls, aperture four to five-toothed — pygmcea. 



Shell oblong-cylindrical, of five whorls, aperture four-toothed — alpestris. 



Shell shortly cylindrical, of four tumid whorls, aperture six-toothed — striata. 



Shell sinistral, stout, of five whorls, aperture seven-toothed — pusilla. 



Shell sinistral, attenuated at base, of five whorls, aperture five-toothed ... — vertigo. 



Shell straightly cylindrical, of six to seven whorls, aperture toothless — edentula. 



Shell oblong-cylindrical, of five narrow tumid whorls, aperture toothless — minuta. 



Inhabiting land. Tentacles not retractile, eyes at their base. 



Carrying a minute oblong shell. Inhabiting wet places CARYCSIUM. 



Shell of five glassy whorls, aperture small, three-toothed — minimum. 



Carrying a much larger fusiform shell. Inhabiting places near the sea CONO VUL US. 



Shell ovate, of six to seven whorls, aperture toothed on both sides — denticulatus. 



Shell oblong, of six to seven whorls, columella four-toothed — myusotis. 



Shell ovate, of six to seven whorls, columella two-toothed — bidentatus. 



Inoperculated. Respiring both air and water. 

 Inhabiting water. Head with muzzle, tentacles various, eyes at their base. 



Carrying a discoid shell of three to seven whorls, tentacles bristle-like PLANORBIS. 



Shell large, ventricose, of five to five and a half striated whorls — corneus. 



Shell small, of four and a half longitudinally striated whorls — albus. 



Shell very small, smooth, of four and a half rounded whorls — glaber. 



Shell very small, nautiloid, of three whorls, epidermis edged with lashes... — crista. 



Shell moderate, depressed, of five whorls, keeled below the centre — carinatus. 



Shell larger, depressed, of five whorls, keeled at the basal edge — complanatus. 



Shell rather small, depressed, of seven very slowly increasing whorls — vortex. 



Shell small, very depressed, of six faintly two-angled whorls — spirorbis. 



Shell rather small, depressed, of seven broad closely coiled whorls — contortus. 



Shell minute, amber-horny, of four convexly sloping whorls — fontanus. 



Shell minute, amber-horny, of four radiately segmented whorls — nitidas. 



Carrying an inflated sinistral shell. Mantle reflected. Tentacles slender... PRYSA. 



Shell ovate, of four glassy whorls, convoluted ventricosely — fontinalis. 



Shell oblong, of five transparent whorls, convoluted attenuately — hypnorum. 



Carrying a horny shell. Mantle rarely reflected. Tentacles flatly triangular LYMNMA. 



Shell obliquely ovate, of four whorls, the last ventricosely inflated — limosa. 



Shell orbicular, of three whorls, the last enormously expanded — auricularia. 



