12 NELSON AND TAYLOR: ON YORKSHIRE MOLLUSCA. 



Var. pulchellum, Jenyns. 



12. Lower Calder—Ossett, L.P. 



13. Airedale — Pond at Potternewton ! 

 22. Denuent — Scarbro', W.B. 



Var. cinereum, Alder, 



Pisidium abditum, Hald. ! 



We are of opinion that Haldeman's F. abditum is the same as 



this species, judging from a study of the description contained in 



Prime's 'Monograph of the Corbiculadse' which we reproduce 



below, and a comparison of authentic specimens received through 



the kindness of Prof. Bolles of Maine. 



Pisidium abditum, Haldeman. — Shell rounded-oval elon- 

 gated, very inequilateral, moderately convex, margins well rounded, 

 beaks placed nearer the posterior side, small, slightly raised; 

 surface smooth, striae not distinct, epidermis variable, generally 

 light straw color; hinge-margin very nearly straight; cardinal teeth 

 small, separate, the anterior tooth larger and more prominent ; 

 lateral teeth small, not much elongated. 



13. Airedale — Leventboipe, common! Stream, Potternewton 

 17. Wensleydale — Snape, H.C. ! 

 22. Derw ent ■Sc^rhxo', W.I!. 



-:o: 



Pisidium pusillum, (Gmelin). 

 Dr. Jeffreys places in the synonymy of this species the 

 Pisidiuin abditum, Hald. We are unable to agree with this view, 

 but consider it the same as P. cinereum. Alder, as pointed out 

 under the head of that variety. 

 3. Vale of Ko/7f— Pannal, W.D.R. ! Wetherby ! 

 7. Went Vale — Ponds, Hazelgreen, near Ackworth, C.A. 

 10. Colne—Uey Wood, local, J.Wli. 



12. Lower Calder — Stanley! Wakefield! 



13. Airedale — Neville Hill, near Leeds ! Osmondthorpe ! Scarcroft ! 

 22. Derwent — Scarbro', W.B. 



24. Holderness—'Lsveii Canal, J.D.B., Keyingham Drain, J.D.B. 



Var. obtusalis, C. Pfeiffer. 



Pisidium ferriigineirm. Prime. 

 Pisidium ventricosum, Prime. 



Considerable diversity of opinion prevails as to the identity 



Trans. Y.N.U.,1S77. Series C 



