PUPA. 155 



Inhabits almost every part of the British Islands, in 

 crevices of rocks and walls, beneath the bark of trees, 

 and under stones and fallen leaves. 



This common species is ovoviviparous, but not 

 prolific ; the young, which do not exceed - five in 

 number, are excluded during the months of July and 

 August, and often remain for a time attached to the 

 shell of the parent. 



The shell of immature specimens is conical and 

 bluntly keeled, and its mouth is furnished with a 

 spiral lamina or plate on the base of the penultimate 

 whorl and on the pillar, as well as with transverse 

 folds similar to those in P. ringens ; it has also a 

 rather deep umbilicus, and is consequently so unlike 

 the adult shell that it has frequently been mistaken for 

 a distinct species. 



Var. I. edentida (toothless), denticle on the base of the penul- 

 timate whorl wanting ; not uncommon. 



Var. 2. alba. — Shell white or colourless. Plymouth and 

 Somersetshire (Norman), Grassmere, Church Stretton, Cardiff 

 and Tenby (J. G. J.), B.C. Pateley Bridge, Yorkshire (Lister 

 Peace), J.C. 



C. Shell cylindrical ; spire short ; mo7ith semi-oval 

 with or without denticles ; outer lip with a strong 

 external rib. 



4. P. margina'ta,* Draparnaud. Pl. IX. 



Body slender, slightly rounded in front, glossy, dark grey, 

 tinged with brown above, paler and covered with minute black 

 specks below, tubercles small but thick-set ; tentacles thick, 

 nearly black, opaque, considerably rounded at the tips, upper pair 



* Margined. 



