NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 63 



Sub-fossil specimens are thrown up by the moles about 

 Askern on what is probably the site of an ancient lake. Mr. 

 Roebuck also found it abundantly with other species in the 

 deposit on the banks of the R. Tutt, near Boroughbridge. 



Like Planorbis corneus this species spins a mucous thread 

 very much less often than Physa and Limn^a, according to the 

 observations of Mr. G. S. Tye. 



Mr. Nelson found a specimen in 1883 with the animal of 

 a bright pink in the same pond at the Black Hills, Leeds, which 

 produced so abundantly in 1879 a similar variation in Planorbis 

 Cornells. 



2. Lune and Ribble — Common in pond by river, Gisburn, April i8th, 



1881, W.D.R. ! 



3. Vale of York — Abundant, but always small, both at Askham and 



Hobmoor ; larger at Bishopthorpe ; immense numbers of exceed- 

 ingly fine specimens in a tiny pond — than which I never saw a 

 filthier — near the south end of Scarborough railway bridge, R. M. 

 Christy, 1881 ; common in ponds in corners of fields, R.M.C., 

 1883 ; common in Askham Bog, June 2nd, 1879, W.D.R. ! 

 also July 1882, G. Webster ! several in a ditch near the Ouse, 

 below York, 1865, W. Whitwell ; pond, Knavesmire ! Clifton 

 Ings, W. C. Hey ; stream, near Church Fenton Station ! pond, 

 near Church Fenton Station, 1879 ! Sherburn, 1870, G. Roberts ; 

 pond, near the Ouse at Selby ! Bishop Dyke, near Selby ! Selby, 

 1867 and 1876, G. Roberts ; Bishop Dyke, near Hambleton, July 

 31st, 1864! Milford Junction, June, 1876, G. Roberts; South 

 Milford, 1876, G. Roberts ; pond at Thorparch ; ditch, between 

 Newton Kyme and Tadcaster ; Boston Spa, 1856, J. Emmet ; 

 Wighill, F. G. Binnie ; pond, at Staveley ! Garforth, April 17th, 

 1876! 



4. Humber—Goole district, R. D.Maxwell, 1876 ; dumps at Carlton Park, 



&c., near Snaith ! Roall, J. W. Wood ! ditch, Barlow Common, 

 Aug., 1881 ! Selby, 1867 and 1876, G. Roberts ; lake, Fryston 

 Park, July 1st, 1871, G. Roberts ; very abundant in ponds, near 

 Fryston Hall, J. Hebden, 1874 5 Newthorpe, Feb. 12th, 1882 ! 

 Ferrybridge, J. Wilcock, 1883 ; abundant in ponds at Castleford ! 

 broad ditches in pastures, north of Castleford, Sept., G. Roberts; 

 stream, Ermine Street, Castleford, March 22nd, 1868 ! Newton, 

 near Castleford, 1870, G. Roberts ; South Milford. G. Roberts, 

 1876. 



5. Hatfield and Thorne—Ahnndznt in ditches bordering Black Bank 



Drain, April 14th, 1883, W.D.R.! common in ditches about Ack- 

 holme; in the River Torne, and in ditches about Blaxton Grange, 

 May 14th, 1883, W.D.R.! ponds. Doncaster ! 



