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 fi-eshwater 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 cantiand). 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. 'i^SS~^7^)^ 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, 190 1). 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. I 97 13
