§8 JOURNAL OF CONCHOLOGY, VOL. I4, NO. 3, JULY, I913. 



of those species which are gradually disappearing and survive only 

 under some favourable conditions in a few isolated localities. 



§ 3.— SPECIES EXTINCT IN BRITAIN. 



1. Pyramidula ruderata Studer. 



A large number of shells of this distinctively Boreal species is 

 found in the deposit at AV^oodston, and they are on the whole very fine 

 examples, the best measurements being 6*35 mm. diameter and 3 mm. 

 altitude. Pyramidula ruderata is very generally considered to be 

 now extinct in the British Isles, and is always rare in fossil deposits. 

 Mr. J. W. Jackson has also recently recorded its occurrence in Cave 

 Earth near Carnforth in North Lancashire, probably of late Pleisto- 

 cene origin {vide "The Lancashire Naturalist," December, 1909). 

 In his "Monograph of the British Land and Fresh-water Mollusca " 

 Mr. J. W. Taylor gives the range of P. ruderata to-day as circum- 

 polar, stretching from Sweden throughout Central and Eastern Europe 

 and Siberia across to Alaska and California. 



2. Helicella (Candidula) candidula Studer.^ 



"Narrowly umbilicated, minutely striate, whitish, unicoloured or 

 variously banded with brown ; whorls 4^-5, slightly convex, the last 

 scarcely deflected in front ; peristome acute, internally thickened. 

 Diam. 9 mill." 



Description from Tryon, " Manjual of Conchology," who figures the 

 species and gives its habitat as " Middle Europe." 



In the Woodston deposit are found a number of small Helicellae of 

 a form which has been noticed in British Pleistocene deposits and 

 been described in the lists as Helicella caperata Mont. Mr. A. S. 

 Kennard, by whom the Woodston shells have been very carefully 

 examined, now admits that H. candidula Studer is the nearest species 

 to them, and to similar shells in his collection from other Pleistocene 

 deposits. They are certainly not the H. caperata of Montagu, being 

 much more compact and globose. Thanks to the kindness of Mr. 

 Edward Collier we have had the opportunity of comparing them with 

 a number of recent European specimens. Mr, J. D. Dean who has 

 examined these shells for me considers the British form as more 

 nearly referable to the var. alpicola Stab, than to the type. In this 

 the whorls are more compressed, the base of the shell flatter, and the 

 umbilicus rather more open. Tryon thus describes this variety : — 



" Var. alpicola Stabile 



" Small, cretaceous, globosely depressed, rather thin, with narrow, 

 pale, interrupted bands, evanescent, aperture more rounded. Diam., 

 6-:; mill." 



I According lo Westeriund, synonymous with Helicella -iinifaSciata Poir. 



