258 ZOOLOGICAL GEOGRAPHY. [part iir. 



known. Balitninus, Stenogyra, and Piqxc are characteristic 

 genera. Bulimus is absent, though one species inhabits St. 

 Helena. The operculated shells are not very well represented, 

 the great family of Cyclostoniidte having here only nine genera, 

 with but one peculiar, Lithidion, found in Madagascar, Socotia, 

 and Arabia. None of the genera appear to be well represented 

 ■throughout the region, and tliey are almost or quite absent from 

 West Africa. 



According to Woodward's Manual (1868) West Africa has 

 about 200 species of land-shells. South Africa about 100, 

 Madagascar nearly 100, Mauritius about 50. All the islands 

 have their jjeculiar species ; and are, in proportion to their 

 extent, much richer than the continent ; as is usually the case. 



The Ethiopian Sub-regions. 



It has been already explained that these are to some extent 

 provisional ; yet it is believed that they represent generally the 

 primary natural divisions of the region, however they may be 

 subdivided when our knowledge of their productions becomes 

 more accurate. 



/. lite East African Sich-rcr/ion, or Central and East Africa. 



This division includes all the open country of tropical Africa 

 south of the Sahara, as well as an undefined southern margin of 

 that great desert. With the exception of a narrow strip along 

 the east coast and the valleys of the Niger and Nile, it is a vast 

 elevated plateau from 1,000 to 4,000 feet high, hilly rather than 

 mountainous, except the lofty table land of Abyssinia, with 

 mountains rising to 16,000 feet and extending south to the 

 equator, where it terminates in the peaks ol Kenia and Kili- 

 mandjaro, 18,000 and 20,000 feet high. The northern portion 

 of this sub-region is a belt about 300 miles wide between the 

 Sahara 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 the 

 mountains of Abyssinia. The greater part of this tract has a 



