14 'NELSON AND TAYLOR : ON YORKSHIRE MOLLUSCA. 



Pisidium roseum, Scholtz. 

 We incline to regard this sliell as having its afifinities more 

 with P. fontiuale, Drap., in accordance with the views of Scholtz, 

 the author of the species, rather than with P. nitidiim^ Jenyns, 

 as held by Dr. Jeffreys. 

 7. V^ent Vale — Stream, Eentle)', near Doncaster ! 



Fa;;a7v UNIONID.P. 



The lakes and rivers of the Western Hemisphere harbour 

 great numbers of this group; comprising, according to the enu- 

 meration of Dr. Isaac Lea of Philadelphia, 720 species, divided 

 into a great number of genera, and exhibiting a very great variation 

 in size, solidity and exterior form and sculpture. 



The total number found in Germany, according to Kreglinger, 

 s fifteen, of which we have but five in England. 



Genus UNIO, Philippson. 



The three species found in this country are all recorded for 

 our county. The U. margaritijer has been placed in another 

 genus, Margarifaiia, Schumacher, by some authoi's, mainly on 

 account of the less developed posterior tooth. 



Unio tumidus, Philippson. 

 Only one variety — the U. radiata of Jeff. — has been found 

 in Yorkshire, out of the many forms that have been described by 

 British and continental authors. 



This and the folIoAving species belong to the genus Lyvuiium, 

 Oken. 

 4. Number— Goole, R.W.M. 



7. Went Vale— Ri\er Went ! 



8. Dearne — Boat pond by Canal, Doncaster, H.F.P. 

 12. Lower Calder — Agbrigg ! 



.1.3- Airedale — Canal, Kirkstall! Rodley ! 



22. Derwent — Scarbro', W.P. (as U. rcsiraiiis, Studer). 



Tr,\ns.Y.N.U., 1S77, Series C 



