XELSOX AND TAYLOR: ON YORKSHIRE MOLLUSCA. 13 



of this form with those inhabiting North America; Dr. Baudon, 

 a great authority on this subject, regards P. ventricosum of Prime, 

 a native of Massachusetts, as the same species, while Dr. Gwyn 

 Jeffreys, disagreeing with this view, thinks P. ferrugijieintt, of 

 Prime more properly referable to it. 



Judging from a comparison of the descriptions and figures, 

 with authentic specimens of P. ohtusale, we incline to the 

 opinion of Dr Jeffreys, but not having had opportunity of 

 comparing authentic specimens of the objects themselves, we 

 cannot speak confidently. 



"We append the descriptions of P. ferrugineinn and P. 

 ventncosuni. 



PisiDiUM FERRUGiNEUM, Prime. — Shell small, rounded-oval, 

 globose, slightly inec^uilateral ; anterior side somewhat produced; 

 margins rounded; beaks tubercular at apex, very distant; surface 

 smooth; epidermis light yellow; hinge-margin rounded; cardinal 

 teeth large, separate, anterior tooth more prominent; lateral teeth 



distinct. 



PisiDiUM VENTRICOSUM, Prime.— Shell small, rounded-oval, 

 globose, ventricose, somewhat oblique, slightly inequilateral, 

 anterior side produced, posterior subtruncate; beaks small, pro- 

 tuberant, distant, situated towards the posterior side; surface 

 smooth, yellow; hinge-margin curved; cardinal teeth separate; 

 lateral teeth short. 



13. Airedale — Leventhorpe! 

 22. Derwent — Scarbro', W.B. 



Pisidium nitidum, Jenyns. 

 Allied to Pisidium ceqiiilaterale of Prime, a North American 

 species. 



6. Iveni — Conisbro', J.W. 



7. Went t''a/e— Ackworth, rare, C.A. 



10. Colne — Elland Canal, common, J.Wh. 



11. Upper Calder — Luddenden, J.C. 

 13. Airedale — Eingley, J.H. 



17. Wensleydale — North Stainley, D. and W. 



22. Deruient — Scarbro', W.B. 



24. H older ness — Spring Dyke, J.D.B., Skidby Drain, J.D.B., Keyingham 

 Drain, J.D.B. 



