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

258 ZOOLOGICAL GEOGRAPHY. [part hi.known. Buliminus, Stenogyra, and Pupa are characteristicgenera. Bulimus is absent, though one species inhabits St.Helena. The operculated shells are not very well represented,the great family of Cyclostomidse having here only nine genera,With but one peculiar, Zithidion, found inMadagascar, Socotra,and Arabia. None of the genera appear to be well representedthroughout the region, and they are almost or quite absent fromWest Africa.According to Woodward's Manual (1868) West Africa hasabout 200 species of land-shells, South Africa about 100,Madagascar nearly 100, Mauritius about 50. All the islandshave their peculiar species; and are, in proportion to theirextent, much richer than the continent ;as is usually the case.The Ethiopian Sub-eegions.It has been already explained that these are to some extentprovisional ;yet it is believed that they represent generally theprimary natural divisions of the region, however they may besubdivided when our knowledge of their productions becomesmore accurate.I. The East African Sub-region, or Central and East Africa.This division includes all the open country of tropical Africasouth ofthe Sahara, as well as an undefined southern margin ofthat great desert. With the exception of a narrow strip alongthe east coast and the valleys of the Niger and Nile, it is a vastelevated plateau from 1,000 to 4,000 feet high, hilly ratherthanmountainous, except the lofty table land of Abyssinia, withmountains rising to 16,000 feet and extending south to theequator, where it terminates in the peaks of Kenia and Kilimandjaro,18,000 and 20,000 feet high. The northern portionof this sub-region is a belt about 300 miles wide between theSahara on the north and the great equatorial forest on the south,extending from Cape Verd, the extreme western point of Africa,across the northern bend of the Niger and Lake Tchad to themountains of Abyssinia. The greater part of this tract has a