NELSON AND TAYLOR: ON YORKSHIRE MOLLUSCA. 31 



13. Airedale — Aire and Cakler Canal near Fleet Mills, Oulton, H.S. ! 

 20. Lower Tees — Appears to be absent from the district, J. W. Watson. 



22. Upper Derwent — It appears in the late Mr. Bean's list of the shells of 



Scarborough, but has not been found by Mr. J. H. Ashford. 



23. Chalk Wolds — Several in dykes near Brough, J.Wh. ! scarce in a ditch 



at Figham, near Beverley, where the water is strongly impreg- 

 nated with iron, J.D.B. ; Beverley, W. C. Hey. 



24. Holderness — Ditch parallel with Leven Canal, J.D.B. ; scarce in 



Barmston Drain, J.D.B. ; Hornsea Mere, W.D.R. ! 



Var. albida Rimmer. 



Shell white. 

 12. Lower Calder — In the Wakefield and Barnsley Canal at Oakenshaw 



Monst. decollatum Jeffr. 



12. Lower Calder — In the Wakefield and Barnsley Canal at Oakenshaw ! 

 :o: 



Family VA L VA TIDyE. 

 Genus VALVATA Miiller. 



Valvata piscinalis (Miiller). 



Valvata Tolosana St. Simon.' 

 Common, but local. 



Judging from specimens of V. Tolosana received from M. 

 Vimont, of Toulouse, we are inclined to consider it as a small 

 variety of this species. 



Dr. Jeffreys considers the Valvata tricarinata of Say, a 

 native of North America, to be a variety of V. piscinalis. The 

 dentition of the two species is different, and the general aspect 

 seenrs to us to favour its specific distinctness from our form. 



It appears to be fond of basking on the soft mud in the 

 sunny shallows of gently flowing streams or ponds. M. Laurent 

 has noticed it to have the power of spinning a downward 

 thread. 



