NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 27 



Var. nov. albida. 



Shell white. 



" Two specimens of this variety labelled Palndina vivipara 

 var., are in the York Museum, where they were deposited by 

 Prof. Phillips. The precise locality is unknown, but it is most 

 probable they are from our county." R. M.C. 



Genus BYTHINIA Gray. 

 The genus Byihinia differs from Paludina not only by its 

 oviparous character, but by the possession in a lobe or pouch of 

 the stomach of a cartilaginous cylinder analogous to the crystal- 

 line stylet of some of the conchifera, and also in the absence of 

 the horny jaws which Pabidina possesses. 



Bythinia tentaculata (L.). 



B. patavina De Betta. 



Very abundant and widely diffused. 



The B. patavina of De Betta is, according to Dr. Kobelt, 

 a variety of this species. 



B. tentaculata, though not a native of North America, has 

 recently been introduced into that country, having been first 

 noticed in 1879, at Oswego, N.Y. ; a little later in the Cham- 

 plain Canal at Waterford and Troy; and early in 1880 was 

 found plentifully in the Erie Canal at Syracuse, N.Y. In some 

 localities it is already abundant. 



It would seem to be generally diffused throughout York- 

 shire, as it is only absent from those districts for which we have 

 been unable to obtain information. 



The Rev. W. C. Hey has found at Askham, near York, a 

 variety with an encircling white band at the periphery, and Mr. 

 R. M. Christy records an elongated form from the River Foss, 



