Geographical Distribution of Mollusca. 437 



lower ground in the district it is extremely local and rare. 

 The association is that of a woodland fauna of a drier type 

 merging on pasture. 



Dominant : — Balea perversa L. Associated species : — 

 Pyramidula ritpestris Drap. | Claiisilia bideiitafa Strom. 



This species, rarely taken here on trees, is abundant in the 

 very driest positions, so abundant, in fact, as to constitute quite 

 a feature. It occurs frequently also on high exposed walls, 

 in clusters under the topmost stones. 



II. — The Oak-Birch Formation. 



(a) Damp : Grassy section. 



Vertigo suhstriata Jeff. 



Acanthinula aculeata Miill. 



These two species while not associated together as a rule, 

 are typical of the Oak-Birch woods. A. aculeata is one of the 

 commonest snails of the Lake District proper, and V. suh- 

 striata seems to be most abundant in the damp woods of the 

 Silurian region, and is only taken locally on the Limestone. 

 A. aculeata is well established also in the Oak-Birch woods of 

 the Lune Valley. 



Dominant : — Claiisilia hidentata Strom. Associated with : — 

 Vitrina pelliicida Miill. 

 Vitrea alliaria Miller. 

 Pyramidula rotundata Miill. 



The extraordinary abundance of this species is most notice- 

 able, especially towards the margins of the woods. It is one 

 which would seem to avoid the Oak-Birch woods of the Dry 

 Heath section. In the damp Ash-Oak woods of the limestone, 

 it is also one of the dominants and like H. arbustorum, there 

 shows a Beech influence, becoming abundant again further north 

 in Beech woods. In the purer Ash woods it is largely replaced 

 by C. cravenensis, and when it does occur tends towards the 

 var. suttoni Westl. 



Helicigona arbustorum L. Associated species : — 



Avion ater L. Pyramidula ritfescens Penn. 



Limax maximus L. Helix hovtensis Miill. 



,, marginatus Miill. 



The true habitat of this species is the wood-margins of the 

 northern Silurian region. It is very abundant in the damp 

 woods of the Lake District, and in a more stunted form it 

 extends its range to a considerable elevation. South of the 

 Kent Valley it persists only in isolated colonies, chiefly in damp 

 meadow grass bordering a wood slope. It is very scarce indeed 

 •on the Limestone. 



1909 Dec. I. 



Hygvomia ritfescens Penn. 

 Pupa cylindracea da Costa. 

 Cochlicopa lubrica Miill. 



