66 NELSON AND TAYLOR ; ON YORKSHIRE MOLLUSCA. 



This is a very active mollusk, and by most authors stated 

 to be ahnost restricted to pure water, but Lindstrom has col- 

 lected it at depths varying from i8 to 36 feet in the brackish 

 water of the Skargard at Stockholm, which is an arm of the 

 Baltic. 



According to our experience, extending over several years, 

 the full-grown animals of this species die off during the latter 

 part of July and beginning of August. 



The body of this species is very bulky, quite double the 

 length of the shell, within which it is almost too large to be 

 concealed. It is affected by an Infusorian {Scyphidia physarum 

 Claparede and Lachmann) which attaches itself to the skin. 



P. fontinalis has been stated by Turton, Gwyn Jeffreys, and 

 others to be normally destitute of epidermis, but this is incorrect, 

 as all our native mollusks have this covering. It is a species 

 much addicted to spiral banding, but these linear revolving 

 whitish lines are not true colour bands, but probably owing 

 to defective secretion of epidermis, caused by injuries to the 

 margin of the mantle. 



It has been observed to vary in length from 6 to 15 mill, 

 the latter being the size of Locard's var. major and Colbeau's 

 var. aplexoideSy which latter seems to connect this species with 

 P. hyp7ioruin, so far as the shell is concerned. 



It is widely distributed in the Palsearctic region and has 

 been reported from Siberia by Westerlund, as well as from the 

 Atlantic Islands, but the specimens from the latter locality have 

 been differentiated by M. Bourguignat as Physa canariensis. The 

 P. tasmanica Tenison-Woods from Van Diemen's Land also is 

 stated by the sponsor to be probably identical with the present 

 species. In the British Isles Jeffreys gives the distribution as 

 everywhere in Great Britain as far north as Aberdeenshire, but 

 Mr. Baillie, of Brora, tells us that the keeper of the Duke of 

 Sutherland's Museum informs him that the late Dr. Gunn found 

 this species ir^ Sutherland, and Da Costa, in his work published 



Trans. Y.N.U., 1890 (pub, 1891). Series C 



