166 PNEUMONOBRANCHIATA. 



This species varies in size and in form, especially 

 of the spire, which is sometimes rather convex, and at 

 others nearly flat : in the latter form, it has been con- 

 sidered as a separate species; and Nilson believes that 

 the shell which Linnaeus described as Helix albella in 

 his Swedish Fauna, is only a young species of the flat- 

 spired variety of this shell. It also varies in the in- 

 tensity of the brown spots on the spire ; sometimes 

 they are diffused and at others entirely wanting, and 

 the shell is sometimes nearly transparent and colour- 

 less. 



46. 2. Zonites umbilicatus. Open Snail, (t. 5. f. 

 45.) Shell convex, somewhat trochiform, black- 

 ish-brown, opake, striolate ; aperture nearly cir- 

 cular ; umbilicus very large. 



Helix umbilicata. Mont. p. 434. t. 13. f. 2. ; Jef- 

 freys, Linn. Trans, xiii. 843. 



Helix rupestris. Drap. p. 82. t. 7. f. 7 — 9. ; 

 Turton, Man. ed. 1. 60. f. 45. 



Zonites rupestris. Leach, Moll. p. 103. 



On elevated rocks, and under the top stones of 

 walls and lofty buildings, always in dry places. 



Animal black-grey, polished ; upper tentacles cylin- 

 drical. 



Shell the tenth of an inch in diameter, elevated on 

 the upper side, with five rounded and deeply divided 

 volutions, slightly striate, of an uniform deep opake 

 chocolate brown; aperture nearly circular, being 

 very little interrupted by the penultimate volution, 

 the margin thin and not reflected ; umbilicus funnel- 

 shaped. 



This shell varies in the elevation and depression of 

 the spire. 



