Fig. 



17. C. pisiDioiDEs, Gray. — C. cornea, var., Brit. Moll. — Ditches and 



ponds, C. Oblique, and light coloured. 



18. C. EivicoLA, Leach. — Cardium nux, etc. — Thames, etc. Large, 



oval, wrinkled. 



19. C. CALicuLATA, Brap. — C. lacustris, etc. — Newcastle, Bristol, etc., 



Mr. With a ridge at the apex. 



20. C. LACDSTRis, Draj}.— pallida, Gray. — Eegent's Park, etc., Mr. 



Oval, light. 



PisiuiUM. Inhabits fresh-water. 



21. P. OBTUSALE, Pfeiffer. — P.pusillum, var.? 



22. P. pusiLLUM, Turton, {Tellina.) — Ci/clas fontinalis KaA gibha. — In 



marshes and ponds at various places, C. Includes P. obtustale ? 



23. P. AMNicuM, Miiller, [Tellina.) — T.rivalis, Cyclas jjalnstris, C. oh' 



liqua. — British rivers, etc., generally. C. obliqua ribbed. 



24. P. NiTiDUM, Jenni/ns. — Battersea, Swansea, etc., C. Thick, dark, 



blunt. 



25. P. Henslowianom, Slieppard, [Tellina!) — Ci/clas appetidiculata, P. 



acutum. — Cambridge, Swansea, etc., E. With a projection on 

 the umbones. 



26. P. PDLCHELLUM, /««_y«». — Cyclas fontinalis, etc. — Various locali- 



ties, C. Ridged. 



27. P. ciNEREUM, Alder. — Cyclas c. — Various localities, Mc. Smooth. 



28. P. ROSEUM, Scholtz. — Various loc, with P. pulchellum and P. niti' 



dum, M. C. Subquadrate ; animal pink. 



