The geographical distribution of animals, with a study of the relations ...

;chap, xi.] THE ETHIOPIAN REGION. 285to introduce, as some writers are disposed to do, a special landconnection or near approach between Madagascar and all thesecountries, independently of Africa ; except perhaps in the caseof the Malay Islands, as will be discussed further on.Land-shells.-^ Madagascar and the adjacent islands are allrich in land-shells. The genera of Helicidas are Vitrina, Helix,Achatina, Columna (peculiar to Madagascar and West Africa),Buliminus, Cionella (chiefly Oriental and South American, butnot African), Pupa, Streptaxis, and Suecinea. Among the Operculatawe have Truncatella (widely scattered, but not African)Cyclotus (South American, Oriental, and South African) ;Cycloplwrus(mostly Oriental, with a few South African) ;Leptopoma(Oriental) ; Megalomastoma (Malayan and South American);Lithidion (peculiar to Madagascar, Socotra, and South-WestArabia) ; Otopoma (with the same range, but extending to WestIndia and New Ireland) ;Cyclostomus (widely spread but notAfrican) ;and Omphalotropis (wholly Oriental and Australian).We thus find the same general features reproduced in the landshellsas in the insects, and the same remarks will to a greatextent apply to both. The classification of the former is, however,by no means so satisfactory, and we have no extensiveand accurate general catalogues of shells, like those of Lepidopteraand Coleoptera, which have furnished us with suchvaluable materials for the comparison of the several faunas.On the probable Past History of theEthiopian Region.Perhaps none of the great zoological regions of the earthpresent us with problems of greater difficulty or higherinterest than the Ethiopian. We find in it the evidence ofseveral distinct and successive faunas, now intermingled ; and itis very difficult, with our present imperfect knowledge, to forman adequate conception of how and when the several changesoccurred. There are, however, a few points which seem sufficientlyclear, and these afford us a secure foundation in ourendeavour to comprehend the rest.Let us then consider what are the main facts we have toaccount for.— 1. In Continental Africa, more especially in the south