8. Patula (Thysanophora) hypolepta (Shuttleworth.)

9. ,, vortex. (Pfr.) Southern Florida and West Indies.

10. Helix microdonta. (Desh.) Bahama Islands, Florida, Texas.

11. ,, appressa. (Say.) Virginia and adjacent states;
perhaps introduced into Bermuda.

{271}
12. ,, pulchella. (Muell.) Europe; very close to _H.
minuta_ (Say) of the United
States. Introduced into Bermuda
(?)

13. ,, ventricosa. (Drap.) Azores, Canary Islands, and South
Europe.

14. Bulimulus nitidulus. (Pfr.) Cuba, Haiti, &c.

15. Stenogyra octona. (Ch.) West Indies and South America.

16. Stenogyra decollata (Linn.) A South European species.
Introduced.

17. Coecilianella acicula. (Muell.) Florida, New Jersey, and Europe.

18. Pupa pellucida. (Pfr.) West Indies, and Yucatan.

19. ,, Barbadensis. (Pfr.) Barbadoes (?)

20. ,, Jamaicensis. (C. B. Ad.) Jamaica.

21. Helicina convexa. (Pfr.) Barbuda.[58]

Mr. Bland indicates only four species as certainly peculiar to Bermuda, and
another sub-fossil species; while one or two of the remainder are indicated
as doubtfully identical with those of other countries. We have thus about
one-fifth of the land-shells peculiar, while almost all the other
productions of the islands are identical with those of the adjacent
continent and islands. This corresponds, however, with what occurs
generally in islands at some distance from continents. In the Azores only
one land-bird is peculiar out of eighteen resident species; the beetles
show about one-eighth of the probably non-introduced species as peculiar;
the plants about one-twentieth; while the land-shells have about half the
species peculiar. This difference is well explained by the much greater
difficulty of transmission over wide seas, in the case of land-shells, than
of any other terrestrial organisms. It thus happens that when a species has
once been conveyed it may remain isolated for unknown ages, and has time to
become modified by local conditions unchecked by the introduction of other
individuals of the original type.