94 MANUAL OF THE MOLLUSCA. 



Extinct Land-S7iails of Madeira. 



Helix delphinula, Lowe. M. 

 „ arcinella, Lowe. P. 

 „ coronula, Lowe. S. Deserta. 

 vermetiformis, Lowe. P. 

 Lowei, Fer. (porto-sanctana, var.?). P. 

 fluctuosa, Lowe (= chrysoraela, Lowe). P. 

 „ psammopliora, Lowe (phlebophora var. ?). P. 

 „ Bowdiohiana, Fer. (punctulata, major ?), M. P. 

 Glandina cylichna, Lowe. P. Santo. 

 Cionella eulima, Lowe. P. 



Pupa linearis, Lowe. M. (= minutissima, Hartm?). 

 „ abbreviata, Lowe. M. 



The problem of the colonisation of these islands receives ad- 

 ditional light from the circumstances noticed at other oceanic 

 islands, especially the Canaries and St. Helena. There is evi- 

 dence that this mountain group has not arisen newly from the 

 sea, and great probability that it has become insulated by 

 the subsidence of the surrounding land.* The character and 

 arrangement of its fauna is probably nearly the same now as 

 when it formed part of a continent, and the diminution of its 

 land-shells in variety and size 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, three hundred and fifty 

 years ago, " that, formerly, the quantity of rain was as great in 

 Madeira, the Canaries, and the Azores, as in Jamaica, but since 

 the trees which shaded the ground had been cut down, rai7i had 

 become much moi-e nire.f 



The Azores are a group of 9 volcanic islands, 800 miles west 

 of Lisbon, the loftiest being Pico, 7,613 feet. The number of 

 land-shells have been recently increased to 68 by Morelet and 

 others, — including Limax 4, Ario7i 3, Testacella 1, Vitrina 7, 

 Helix 30, Bidimus 10, Zua 1, Pupa 8, Balea 1, Auricula 3. Of 

 these 28 are found in Europe, 7 in Madeira, 4 in the Canary 

 Islands, and the remaining 29 are peculiar. 



The Canary Islands are sixty miles west of Africa, with a 

 temperature of 60°— 66^ in the coolest half year, and 78°— 87^ 

 in the hottest. The land-snails are about 80 in number, in- 

 cluding Helix 50, Nanina 1, Vitrina 3, Bulimiis 16, Achatina 3, 

 Pujpa 5, Limax 1, Phosphorax 1, Testacella 2, Cryptella 1, and 



* See the observations of Mr. James Smith, and of Sir C. Lyell and Mr. Hartung 

 (Geol. Jour. 1854). 



t Cosmos, ii. 660, Bohn ed. It seems likely that Jamaica itself has since undergone 

 a similar change ; the fall of rain is stated to be 4912, whilst in the neighbouring 

 islands it exceeds lUO inches. 



