588 MANUAL OF THE MOLLUSCA. * 



may be the result of a modern change of physical conditions brought about 

 by human agency, as at St. Helena. The annual fall of rain is now 

 29.82 inches, whereas it was remarked by Columbus, 350 years ago, "that, 

 formerly, the quantity of rain was as great in Madeii*a, the Canaries and the 

 Azores, as in Jamaica, but since the trees, which shaded the ground, had 

 been cut down, rain had become much more rareT * 



The Azores are a group of 9 volcanic islands, 800 miles ^Y. of Lisbon, 

 the loftiest being Pico, 7,613- ft. Only 13 land-shells have been found, of 

 which 3 are common to the Canaries, 1 to the Canaries and Madeira, 3 to 

 Madeira, 1 to the Canaries and C. de Verdes, and 2 are peculiar, viz. : 

 Helix Azorica and Bulimus cyaneus. Helix harbnla is also found in Por- 

 tugal, H. pisana and cellaria are common to Madeira and Europe, and 

 H. aspersa has been introduced recently. 



The Canary islands are 60 miles W. of Africa, with a temperature of 

 60^—66^ in the coolest half-year, and 78°— 87° in the hottest. The landsnails 

 are about 80 in number, including Helix 50, Nanina 1, Vitrina 3, Bulimus 

 16, Achatina 3, Pupa 5, Limax 1, Phosphorax 1, Teslacella 2, Cryptella 

 1, and 4 CydostomidcB. Of these, 60 are peculiar, 12 are common to S. 

 Europe, and 4 to the West Indies? 1 to Morocco, 1 to Algeria (also Euro- 

 pean), and 1 to Egypt, The fresh- water shells are Phusa 2, Ancylus 1. 



Helix ustulata and Mc Andrei are peculiar to the rocky islets known as the 

 "Salvages" north of the Canaries. 



The absence of W. African land-shells and the presence of W. Indian \ 

 species may be explained by the currents, which come from the Antilles, as | 

 shown on the map. f Some of the European species may have been intro- \ 

 duced {e. g. Helix lactea, pisana, cellaria) ; but the presence of 20 Lusita- .■ 

 nian species, in a total of 80, is too remarkable to be accidental, ■ 



The Cape de Verde Islands, although much further to the south, are also : 

 much farther from the continent, being 320 miles West of C. de Verde; the I 

 mean temperature is 65° — 70°, and the vegetation, as Dr. Christian Smith \ 

 remarked, is more like that of the JMediterraneau coast than W. Africa. Of \ 

 the 12 land-shells, two are common to the Canaries and Azores. 



Lusitanian species of wide distribution. 



Helix amanda, Sicily — Palma. Ji 



„ planata, IMorooco — Canaries. •• | 



,, lenticula, S. Europe — Madeira — Canaries. ^ 



,, rozeti, Sicily, Morea — Algeria — C. de Verde — Canaries, I 



„ lanuginosa, Majorca — Algeria — Palma, \ 



* Cosmos, II. 660, Bohn ed. It seems likely that Jamaica itself has since ^J 

 undergone a similar change; the fall of rain is stated to be 49.12. whilst in the neigh- 

 bouring islands it exceeds 100 inches. 



+ Long before the discovery of America it was observed that the westerly gales Ij 

 •washed ashore stems of bamboos, trunks of pines, and even living men in canoes. 

 —Humboldt, II. p, 462. 



I 



