cHAr. XVI THE BRITISH ISLES 357 



thus lead, ultimately, to a more accurate knowledge of the 

 facts. It is only by obtaining a full knowledge of varieties, 

 their distribution and their comparative stability, that we 

 can ever hope to detect the exact process by which nature 

 works in the formation of species. 



List of the Species and Varieties of Land and Freshwater 



Shells which, so far as at present known, are believed to be 



Peculiar to the British Isles or not found on the Continent. 



LlMACID^. 



1 . Limax marginatus, var. M ACULATUS. Ireland ; frequent, very distinct, 



2. ,, ,, ,, decipiens. Ireland and England. 



3. ,, flavus, far. suffusus. England ; Melanic form. 



4. ,, ,, ,, griseus. England ; Melanic form. 



5. Agriolimax agrestis, var. niger. Yorkshire. Melanic. Azores. 



6. ,, ,, ,, GRISEUS. England. Melanic. 



7. Amalia gagates, var. rava. W. of England. 



8. ,, sowerbyi, var. rustica. England. 



9. ,, ,, ,, NiGRESCENS. Surrey and Middlesex. 



10. ,, ,, ,, BicoLOR. Ealing. 



11. Hyalina crystallina, var. complanata. Near Bristol. 



12. ,, fulva, var. alderi. 



13. Yitrina pellucida, var. depressiuscula. S. England, Wales. 



Helicid^. 



14. Arion ater, var. albo-lateralis. England, Wales, Isle of Man : 



very distinct. 



15. ,, liortensis, var. fall AX. England. Common at Boxliill. 



16. Geomalacus :iiACUL0SUs. Kerry and Cork. Three varieties have 



been described, one of which occurs in Portugal. 



17. Helix aspersa, var. lutescens. England. Kot rare perhaps in 



France. 



18. ,, nemoralis, var. hibernica. Ireland. 



19. ,, rufescens, var. manchesteriensis. England. 



20. ,, hispida, var. subglobosa. England. 



21. ,, ,, ,, depilata. England. 



22. ,, ,, ,, MINOR. England, Ireland. 



23. ,, granulata, var. cornea. Lulworth, Dorset. 



24. ,, virgata, var. subaperta. Bath. 



25. ,, ,, ,, subglobosa, England, Wales, Bantry Bay. 



26. ,, ,, ,, carinata. Wareham, Dorset. 



27. ,, caperata, var. major. England, AVales, Scotland. Distinct. 



28. ,, ,, ,, NANA. England. 



29. ,, ,, ,, suBSCALARik Wales, Ireland. 



30. ,, ,, ,, ALTERNATA. England, Kent. 



31. ,, acuta, var. nigrescens. England. 



PUPID^. 



32. Pupa anglica, var. pallida. Not rare. 



33. ,, lilljeborgi, var. bidentata. Ireland. 



