6o NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 



diaphanous, and suffused with a shght tinge of pink. The 

 operating cause would appear to have been but temporary, as 

 not a single individual exhibiting the variation could be found 

 during the following season. 



Mr. Butterell has also recorded the finding in Spring Dyke, 

 near Hull, in 1879, of a number of specimens exhibiting the 

 same peculiarities. 



3. Vale of York — River Fosse near York, in great plenty (Martin Lister, 



1678). Common about York, Strensall, Askham, Hobmoor, 

 stream beside the Foss, Bishopthorpe, &c., especially good at times 

 near the latter place, R.M.C., 1881 ; ditches, York, J. Emmet, 

 1883 ; one place near York, W. H.B. ; Middlethorpe Ings, York, 

 1865, R. Whitwell ; stream near Bishopthorpe, R. M.C.; pond by 

 Clifton Ings, H. Richardson ; Knavesmire, J. Emmet ; Askham 

 Bog, in one of the deeper and more open ditches, R.M.C., 1879 ! 

 Askham Bog, abundant, June 2nd, 1879, W.D.R.! encrusted 

 specimens in a small reedy expansion of a ditch by the Foss, in a 

 field above Yearsley Bridge, York, 1858, W. Whitwell ; Strensall 

 Common, W.C.H., 1879 ; Strensall Common, local, but abundant, 

 the specimens unusually fine, W. Hewett, 1884 ; pond, near the 

 Vicarage, Riccall, June, 1879 ! Tockwith ! Milford House, near 

 Church Fenton, one specimen, August 20th, 188 1, W.D.R. I 

 stream crossing road near Mattram Hall, Sherburn, April 1 2th, 

 1868 ! Bishop Dyke, near Hambleton, July 3rd, 1864, and April 

 I2th, 1868 ! Milford Junction, June, 1876, G. Roberts ; Garforth, 

 April 17th, 1876 ! 



4. Number — Abundant in a pond at Castleford, evidently introduced, J. H., 



1874 ; plentiful, in various stages of growth, in a shallow muddy 

 pond in the pastures near the new iron railway bridge at Castle- 

 ford, June iSth, 1885, G. Roberts ; ditches in pastures north of 

 Castleford, G. Roberts ; pond near Fairburn, mostly young, June, 

 1885, G. Roberts ; Breighton, near Bubwith, Sept. 4th, 1880, 

 W.R.D. I Newsholme Road, near Howden, January! Goole 

 district, R.D.M. ; Wressle, 1884, G. Roberts ; Selby, 1876, G. 

 Roberts ; ditch, by canal, Selby ! South Milford, G. Roberts, 

 1876. 



5. Hatfield and Thome — Ditch, parallel with Black Bank Drain, young 



ones plentiful, no old ones seen, April 14th, 1883, W.D.R. ! 

 Potteric Carr, J.E., 1884. 



7. Went Vale — Abundant in ditch, Cowick Park, June 17th, 1882, 

 W.D.R.! Askern Pool, E. Lankester's Askern, 1842; Askern, 

 H.S., 1882! South Elmsall, J.W., 1885; Pontefract, J. W. 

 Wood! 



Trans.Y.N.U., 1884 (pub. 1886). Series C 



