BYTHINIA. 29 



ternally with a strongish white rib ; inner lip joined to the base 

 of the penultimate whorl and forming with the outer lip a com- 

 plete peristome ; umbilical chink very narrow ; operculum thick, 

 oval, angulated above, centre depressed, finely striated concen- 

 trically, and made up of a series of plates rising one above 

 another, which have been formed by the animal at different 

 stages of its growth. 



Inhabits slow-running streams, ponds, and ditches 

 in most parts of England, Wales, and Ireland ; in 

 Scotland, where it seems to be very local, it has 

 been observed in Aberdeenshire ; the Rev. J. McMur- 

 trie informs me that it occurs abundantly in the 

 canal at Edinburgh, and I have found it in Dumfries- 

 shire. 



It is an inactive and irritable mollusc ; when 

 touched it instantly retreats into its shell. It fre- 

 quently floats on the under surface of the water, 

 and when crawling carries its snout turned upwards. 

 In winter the animal is said to assume "a yellowish 

 chestnut-colour" (Daniel), B.C., Supplement, vol. v. 

 p. 151. 



Var. i. ventricosa (Menke). Shell white, whorls more tumid. 

 Devonshire, Bristol, Wandsworth, Richmond, Surrey, B.C. 

 Near Birmingham (G. Sherriff Tye), J.C. 



Var. 2. excavata. Whorls rounder; suture deeper. Wool- 

 wich, Cardiff, Co. Armagh, B.C. Kirkthorpe, near Wakefield 

 (J. Hebden)', near Birmingham (G. Sherriff Tye), J.C. 



Var. 3. albida. Shell white. Near Birmingham (G. Sherriff 

 Tye), J.C. Near Colchester (Laver). 



Monst. decollata. Upper whorls wanting in half-grown and 

 adult specimens, their place being supplied by a nearly flat 

 semispiral plate, as in Bulimus decollatus. Woolwich, Cardiff, 

 Co. Armagh, B.C. Near Birmingham (G. Sherriff Tye), near 

 Wakefield (J. Hebden), J.C. 



