LUSITANIAN REGION. 387 



or geographical varieties. Helix siibpUcata and papilio are found on the 

 Uheo Baxo; H. turricula on Cima. Of the total number (132) 111 

 species are peculiar to the Madeira group ; 5 are common to the Canaries ; 

 4 to the Azores, and 1 to the Guinea coast; 11 are common to S. Europe, 

 besides 2 Limnmds, and 7 slugs, which may have been recently introduced 

 viz. : — 

 Arion empiricorura Helix cellaria. Zua lubrica, var. 



Limax variegatus. ., crystallina. „ folliculus. 



„ autiquorum. „ pisana. Bulimus decollatus. 



,, agrestis. ,, pulchella. „ venti-osus, Fer. 



„ gagates. „ lenticula. Balaea perversa (p. 106). 



Testacella Maugei. ( „ lapicida,/o.ssi;). Limnaea truncatiUa 



,, haliotidea. Ciouella acicula. Ancylus fluviatilis. 



Great quantities of dead shells of the land-snails are found in ancient 

 sand-dunes near Cani9al, at the eastern extremity of Madeira, and in Porto 

 Santo, including 64 of the living species and 13 which have not been found 

 alive. As the fossil examples of several species are larger than their living 

 descendants, it is possible that some of those reputed to be extinct have only 

 degenerated. It is a remarkable fact that some of the commonest living 

 species are not found fossil, whilst others, now extremely scarce, occur abun- 

 dantly as fossils.* 



Extinct land-snails of Madeira. 

 Helix delphiiiula, Lowe. M. 

 ,. arcinella, Lowe, P. 

 ,. corouula, Lowe, S. Deserta. 

 „ vermetiformis, Lowe, P. 



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

 flactuosa, Lowe (=chrysomela, Lowe^ P. 

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

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

 Glandina cylichna, Lowe. P. Santo. 

 Cionella eulima, Lo we, P. 



Pupa linearis, Lowe. M. ( = miautissima, Haitm ?) 

 „ abbreviata, Lowe. M. 



The problem of the colonization of these islands receives additional light 

 from the circumstances noticed at other oceanic islands, especially the 

 Canaries and St. Helena. There is evidence 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.f 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 . 



* Helix tiarella, W. and B. was supposed to be extinct, but in tlie last summer, 

 (1H55) Mr. WoUaston detected it alive in two almosi inaccessible spots on tiie north 

 coast of Madeira: it is not a native of the Canaries. 



t See the Observations of Mr. James Smith, and of Sir C. Lyell and Mr. Hartung 

 (Geol. Journ. 1854). 



S 3 



