62 NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 



Var. major Pascal, 1873. 



Planorbis grandis Dunker. 

 Planorbis inflatus Dunker. 



Var. a MAJOR, diam. 31 mill., haut. 14 mill. — Pascal, Moll. 

 Haute Loire et Paris, p. 56, 1873. 



Dr. Kobelt quotes Planorbis grandis and P. inflatus of 

 Dunker as synonyms of this variety. 



Mr. E. J. Lowe records that specimens living in a muddy 

 brook at Beeston, Notts., into which a constant supply of warm 

 water is discharged, attained a diameter of i^ inches. 



3. Vale of York. — Strensall Common, July, 1880 ! some specimens 34 mill, 

 diam. 

 23. Chalk V/olds — Three specimens gathered at Boynton Fish Ponds, on 

 Aug. 6th, 1883, were of the following dimensions, 33 x 13, 35 x 14, 

 and 35 X 14 mill. ! and Mr. L. B. Ross informs us he has seen 

 larger from the same locality. 



Var. minor Pascal, 1873. 



Planorbis similis Bielz. 



Var. {■ MINOR, diam. 18-20 mill., alt. 7-9 mill,, with a very 

 black and rather broad border encircling the aperture, and 

 appearing on the callosity which unites the two edges. — Pascal, 

 Moll. Haute Loire et Paris, p. 56, 1873. 



13. Airedale — A few have been obtained from the pond at Black Hills, 

 near Leeds. 



Sub-genus BATHYOMPHALUS, Agassiz. 



Shell depressed, not keeled, widely and deeply umbilicated below, the 

 whorls increasing very slowly, the last a trifle broader than the penultimate ; 

 aperture narrowly semilunar (Moquin-Tandon, ' Hist. Nat. d. Mollusq. terr. 

 et fluv. de France,' ii., p. 445). 



Planorbis contortus (L.). 



Widely distributed and locally common. 



This species is widely dispersed in Yorkshire, being found 

 in seventeen of the twenty-five districts into which the county 

 is divided. It is local and usually abundant where it occurs. 



The specimens from Dringhouses Bog near York, collected 

 in June 1879, seem to be referable to Arnould Locard's variety 

 sni>ri(/a. 



Trans. Y.N U., TsS4 (pub. 1886). Series C 



