an introduced colony of _Helix nemoralis_ at Lexington, Virginia,
presents numerous varieties among which are several which do not occur in
Europe.[84] The following list is therefore given in the hope that it may
be useful in calling attention to those varieties which are not yet
positively known to occur elsewhere than in our islands, and {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.

LIMACIDAE.

1. Limax marginatus, _var._ MACULATUS. Ireland; frequent, very
distinct.

2. ,, ,, ,, DECIPIENS. Ireland and England.

3. ,, flavus, _var._ 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. Vitrina pellucida, _var._ DEPRESSIUSCULA. S. England, Wales.

HELICIDAE.

14. Arion ater, _var._ ALBO-LATERALIS. England, Wales, Isle of Man;
very distinct.

15. ,, hortensis, _var._ FALLAX. England. Common at Boxhill.

16. GEOMALACUS MACULOSUS. Kerry and Cork. Three varieties have been
described, one of which occurs in Portugal.

17. Helix aspersa, _var._ LUTESCENS. England. Not 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.