KENNARD : HOLOCENE NON-MARINE MOLLUSCA OP ENGLAND. 249 



and in a Bronze age tumulus in Somerset, but being unknown from 

 any pre-Koman deposit over the greater part of England, it bas 

 proved a useful zone fossil. Since this species does not burrow to 

 hibernate, human habitations and their surroundings furnish 

 excellent hibernacula, and the large population and high civilization 

 which existed in England in Roman times will account for its wide 

 distribution during that period, while the recent extension of its 

 range may well be attributed to the same causes. 



Fruticicola {Capillifera) striolata (C. Pfr.) is known from several 

 early Holocene deposits in the South of England, so that it is un- 

 doubtedly a true native, but its modern distribution differs greatly 

 from the fossil records, and its area of distribution was probably 

 greatly increased during Roman and more modern times. A. W. 

 Stelfox has suggested that it is quite a modern introduction into 

 Ireland {Proc. Malac. Soc. Lond., vol. x, 1913, pp. 290-1), a view 

 strongly supported by the geological evidence {Proc. Geol. Assoc, 

 vol. xxviii, 1917, p. 167). It has a marked partiality for the 

 neighbourhood of human habitations, especially gardens. 



Paludestrina jenkinsi (Smith) is a puzzling form. It is known 

 fossil from Barking (Essex), Blythburgh (Suffolk), and Clevedon 

 (Somerset). The two former deposits are mediaeval, and there is 

 no evidence as to the age of Clevedon, but it is clear 

 that the theory that it was introduced into this country 

 during the last century must be discarded. One thing, however, 

 is certain, and that is that it has enormously increased its range 

 during the last fifty years. Now that this species is known from 

 Denmark and Germany, it will be interesting to see if it will be able 

 to extend its range in those countries in so rapid a manner. There 

 are a number of species which are apparently more abundant at 

 the present day than formerly. These include Helicella rogersi 

 (B. B. W.), H. alliaria (Mill.), Pyramidula rupestris (Drap.), Helix 

 hortensis, Miill., Ena ohscura (Miill.), Lauria cylindracea (Da Cost.), 

 Ahida secale (Drap.), Balea perversa (Linn.), Limncea glabra (Miill.), 

 Dreissensia polymorpha (Pall.), and Sphcerium lacustre (Drap.). All 

 these forms are decidedly rare as fossils, though the records show 

 that there has been no great, if any, extension of range. Helicella 

 rogersi (B. B. W.) is absent from all the Kentish rain- washes, yet 

 at the present day it is very common on the chalk hills. Its 

 occurrence in an early Holocene bed at Walton Heath, Surrey, as 

 well as other records, show that it is a native. 



Helicella alliaria (Miill.) is decidedly rare as a fossil, though the 

 records prove that it was widely spread. It has a curious partiality 

 for pigsties, scarcely a natural habitat. 



Why Helix hortensis, Miill., should be so rare as a fossil is a problem 



I cannot answer and in only one Holocene deposit was it common, 



the early Neolithic flint mines of Grimes Graves, Weeting, Norfolk. 



It does not occur in many of the Kentish rain-washes, though living 



VOL. XV. — JUNE, 1923. * 17 



