g4 MANUAL OF THE MOLLUSCA. 
Extinct Land-snails of Madesra. 
Helix delphinula, Lowe. M. 
» arcinella, Lowe. P. 
coronula, Lowe. S. Deserta. 
vermetiformis, Lowe. P. 
Lowei, Fer. (porto-sanctana, var.?). P. 
fluctuosa, Lowe (= chrysomela, Lowe). P. 
3, psammophora, Lowe (phlebophora var. ?). P. 
» Bowdichiana, Fer. (punctulata, major ?), M. P. 
Glandina cylichna, Lowe. P. Santo. 
Cionella eulima, Lowe. P. 
Pupa linearis, Lowe. M. (= minutissima, Hartm ?). 
3 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, rain had 
become much more rure.+ 
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, Arion 3, Testacella1, Vitrina 7, 
Helix 30, Bulimus 10, Zua1, Pupa 8, Baleal, Auricula3. Of 
these 28 are found in Europe, 7 in Madeira, 4 in the Canary 
Islands, and the remaining 29 are pecuhar. 
The Canary Isiands 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 Heliz 50, Nanina 1, Vitrina 3, Bulimus 16, Achatina 3, 
Pupa di, Limax1, 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). 
¥ Cosmos, ii. 660, Bolin ed. It seems likely that Jamaica itself has since undergone 
asimilar change; the fall of rain is stated to be 49°12, whilst in the neighbouring 
islands it exceeds 10) inches, 
