THE CONCHOLOGIST, 



19 



Period had a degenerative effect upon the 

 molhisca, Mr. A\'ood\vard appears to think 

 when he remarlcs : — "Speaking broadly, the 

 Pleistocene Molluscan fauna appears to have 

 been finer than the existing one, — and 

 it really seems as if our non-marine mol- 

 lusca had deteriorated both in size and 

 number." 



This, however, does not answer satisfac- 

 torily for the extinction in the British area 

 of the species mentioned. There is some 

 evidence that during the latter part of the 

 Glacial Period, a considerable portion of 

 Great Britain was submerged to a depth of 

 2,000 feet, when only the highest mountain 

 tops would be visible as rocky islets. This 

 submergence would destroy the greater part, 

 if not the whole, of the molluscan fauna 

 existing on the area. Upon its subsequent 

 elevation and union with the continent, the 

 migration of, or dispersal of continental forms 

 into the British area would commence. 

 From other evidence it would appear that 

 sufficient time did not elapse for the 

 migration of a complete continental fauna, 

 before a subsidence again occurred, when 

 the waters of the ocean intervened, cutting 

 off the further influx of purely terrestrial life 

 into the British area. 



Would this view of the non-migration 

 back again into this area account for the 

 extinction of the seven species of non- 

 marine moUusca enumerated ? 



THE LAND AND FRESHWATER MOLLUSCA 

 OF OXFORDSHIRE. 



By W. E. Colmnge. 

 Colli iniicd from pai^c 17. 



Van albinos, Moq. 



4. Deddington. — Few specimens. 



6. Oxford. — " Occasionally found with the 

 ordinary form, Wytham Hill, and near 

 Islip" (S. Spencer Pearce). 



Hyalina glabra, Studer. 

 In Oxfordshire its distribution is by no 

 means general. 



5. Bicester. — Two or three specimens, 1887. 



6. Oxford. — Recorded by the Rev. S. Spencer 



Pearce from Wick Copse and Wood- 

 eaton. 



7. Swincomb. — Rare, sparingly met with. 



Hyalina allaria, Miill. 

 A somewhat local form, but not at all rare. 

 I. Banbury. — Fairly common. 

 3. Wychwood and Chadbury. — Sparingly 



met with. 

 6. Oxford. — Commoner in this district than 



anywhere else. 



8. Henley. — Mapledurham and Henley 



(Whiteaves, 1S57). 



Hyalina nitidula, Drap. 

 I have not been successful in finding this 

 species in districts 4, 5' 7> or §. Where it 

 occurs I have generally found it plentiful. 

 Small specimens of Hy. cellarius are, I have 

 found, often apt to be mistaken for this 

 species. 



1. Banbury. — Plentiful. 



2. Chipping Norton.— Occurs very plentifully. 



3. Wychwood and Charlbury.— Ditto. 



