MOLLUSCS 



NON-MARINE 



Except in the northern or lake-district portion of the county there is 

 little limestone, while the drift deposits that mask the plains, the peat-beds, 

 and the sand-dunes of the coast do not offer favourable conditions for mollus- 

 can life. Hence land-snails are not individually very numerous in Lancashire. 

 That so many species are recorded is we believe mainly due to the industry 

 and enthusiasm that seem to permeate north country naturalists. 



The freshwater shells on the other hand abound, while it is among the 

 brackish water forms that the few possible additions to the list are chiefly to 

 be sought. 



Of the 140, or so, species known to occur in the British Islands, 106 

 have been recorded for Lancashire. This is a very considerable proportion, 

 and the number is not likely to be much increased by future researches. 



Three aliens of note have invaded the county : Specimens of Pupa 

 quinquedentata (Born) [= cinerea, Drap.] are recorded by Mr. Wrigglesworth 

 from Church, and by Mr. Long from near Stonyhurst, whither they have 

 probably been brought from the continent by some student. Physa heterostropha, 

 Say, a North American freshwater species, has been taken in canals at 

 Gorton and Droylsden, and may ultimately become naturalized. Another 

 freshwater form from the United States, Planorbis dilatatus, Gould, is almost 

 certain to do so ; it has been found in abundance at Pendleton, Gorton, 

 Burnley, Stoneyholme, and Gannow, and is supposed to have been introduced 

 adhering to cotton bales. 



The more representative Lusitanean or south-western forms are absent, 

 and the white-banded snail (Helicella virgata) and the heath snail (H. itala), 

 so abundant in our southern coasts, occur but sparsely on the sand hills of the 

 Lancashire sea-board ; while the common garden snail (Helix aspersa] is not 

 so universally distributed as it is further south. 



Certain well-known southern or continental forms are missing from the 

 fauna, such as the Kentish snail (Helicella cantiana}. 



On the whole, therefore, the assemblage may be considered to present a 

 normally British facies. 



The literature on the subject consists largely of scattered notes, the most 

 complete list for the county being a paper by Mr. R. Standen (Naturalist, 

 1887, pp. 155176), while the Manchester district has been dealt with by 

 Mr. C. Oldham (Science Gossip, xx. 213), and the neighbourhood of Burnley 

 by Mr. F. C. Long (Journ. Burnley Lit. & Phil. Soc., No. 17, 1901). 



For the sake of uniformity the same nomenclature is here followed as in 

 other volumes of the Victoria County Histories, but for the most recent 

 information on this subject reference should be made to the List published 

 by the Conchological Society. 



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