3i8 



Geographical Distribution of Mollusca. 



Planoyhis umhilicatus (Miiller). Associated with : — 



Liuincea pereger Miill. I Aplecta hypnorum L. 



Plaiiovhis spirovhis L. | Pisidium piisillum Gmelin, 



It is the var. rhombea Turton of this species which occurs 

 near the Lune Estuary in the drains and ditches which are 

 in all probability subject to an inrush of salt water in flood 

 seasons. Var. rhombea also occurs in the salt-marshes of the 

 Thames Estuary, in salt-marshes at Blytheburgh (Suffolk), 

 and in the marshes between Lewes and Newhaven (Sussex). 



§ 2. Sand Dunes — Xerophile. None in the district. 



DRY GRASSLANDS. 

 Calcareous Pastures. Sub-Xerophile and Calco-phile. 

 I. Carboniferous Limestone. (Examples at Silverdale, 

 Grange, etc.). 



Pyramidula rupestris Drap. Associated species : — 



Agviolimax agrestis L. I And locally 



Pupa cylindracea da Costa. | Pupa muscorum L. 



This is one of the most characteristic species of the Lime- 

 stone region, and has an uninterrupted range. It is essentially 

 a Helix of the rock surfaces which it much resembles. Even 

 during the heat of the day it will remain exposed to the sun's 

 rays while the Pupae retreat into the crevices of the rock or the 

 roots of the grasses. Pupa muscorum is more abundant on the 

 lower sea-ward pastures than on the higher ground. Pyramidula 

 rupestris with Pupa cylindracea is a distinctive feature of 

 Limestone pasture at high altitudes, though P. rupestris alone 

 even extends to the summit of Skiddaw (3054 feet) on Ordovi- 

 cian Grits. 



Helicella caperata Mont 



(a) In conjunction with Thymus serpyllum is associated 

 with :— 



Agriolimax agrestis L. | Helicella itala L. 



Avion intermedius Normand (rare). ' Hygvomia hispida L. 



In conjunction with Tanacetum vulgar e is associated 

 with : — 



Agriolimax agrestis L. 

 Arion ater L. 

 Vitrea cellaria Miill. 

 nitidula Drap. 



Hygromia rufescens Penn. 



hispida L. 

 Helix aspersa Miill. 



Naturalist, 



