32 VALVATIDAZ. 



placed at right angles to the stalk; branchial appendage as 

 long as the tentacles ; foot six times as broad as the snout, from 

 which it is entirely separated, deeply bilobed in front and rounded 

 behind, tail long, nearly covered by the operculum ; lingual 

 ribbon long, central tooth subquadrate, its base produced, hooked 

 and denticulated ; uncini three on each side, lanceolate, toothed 

 on both sides. 



Shell globose, depressed, rather thick, semitransparent, horn- 

 colour with a yellowish or brownish tinge, with fine, regular 

 close-set striae in the line of growth, and more or less ridged 

 spirally ; whorls 5-6, tumid, rounded, the body whorl occupying 

 more than one-half of the length of the shell ; spire depressed 

 and obtuse ; suture deep, straightish ; mouth round ; outer lip 

 thickish, reflected ; inner lip forming with the outer lip a com- 

 plete peristome ; umbilicus round, not very large but exceedingly 

 deep ; operculum round, its centre somewhat depressed, with a 

 spire of from 10-12 volutions whose outer edges slightly overlap 

 one another. 



Inhabits ponds, canals, and sluggish . streams 

 throughout the British Isles. It is inactive and ir- 

 ritable. Moquin-Tandon says it breeds during the 

 months of May, June, July, and August, and that 

 the eggs, to the number of about seventeen, are en- 

 closed in a capsule, which is fixed to some solid 

 substance. The fry are hatched after an interval of 

 from fifteen to sixteen days, and on emerging from 

 the egg are provided with a shell consisting of a 

 whorl and a half; it is delicately striated, and so 

 transparent that the little animal, one half of which 

 is yellowish and the other greenish, is distinctly 

 visible within. 



Var. i. depressa Spire more depressed; umbilicus larger; 

 occurs in many parts of Great Britain, but it is local. 



Var. 2. subcylindrica. Spire more produced, apex flattened ; 

 umbilicus small. Grassmere (J. G. J.), B.C. River Went (J. 

 Hebden), J.C. 



