NELSON AND TAYLOR: ON YORKSHIRE MOLLUSCA. 77 



Dr. Brot and Herr Clessin have separated as a distinct 

 species the L. peregra existing in the depths of Lake Geneva. 

 Mr. Thompson also records a deep water form of this shell 

 from Lough Neagh, Ireland, and more recently Rev. W. C. Hey 

 has remarked on a similar habit in River Ouse specimens at 

 York. 



Dr. Gwyn Jeffreys regarded as synonymous with our 

 species the Z. columella of Say, which, under the various names 

 of L. chalybea Gould, L. acuminata, surcitiifonnis, and columell- 

 aris Adams, L. strigosa, coarctata and casta of Lea, Z. navuula 

 Valenciennes, and Z. macrostoma of Say, is distributed over 

 large tracts of North America. 



The Z. gocdwhiii E. A. Smith, from Japan, is considered 

 by Mr. Nelson, after an inspection of the type specimens in the 

 British Museum, to be identical with our species. 



Several parasites have been recorded as found infesting 

 Z. peregra or its varieties: — Linstow describing Cercaria pugio 

 and Distoma limncece-ovatce, as infesting the van ovata, and also 

 recording the finding of encapsuled embryos of Gordius aquaticus 

 in the var. vulgaris. The larva of Chironofnus prasinusho.s been 

 found in the body of var. ovata by Mr. H. P. Fitzgerald. 



The earliest geological formation containing Z. peregra is 

 the Red Crag, at Butley, in Suffolk. It has been found in 

 Yorkshire in the peat-bed beneath the glacial drift in the Horn- 

 sea mud-cliffs, as well as in the mud-cliffs on the north bank of 

 the River Wharfe at Carthick Ford, and in a deposit on the banks 

 of the River Tutt, near Staveley, where it is associated with a 

 number of other freshwater species. 



It is, however, worthy of remark that the Rev. E. S. 

 Dewick slates that- the Barnwell Gravel fossils of this species 

 cannot be separated from those of undoubted Z. auricularia. 



Hazay states that he has verified by actual demonstration 

 that the typical form of Z. peregra is jjroduced by living in 

 'hard' running water containing much carbonic acid, and that 



