258 
ZOOLOGICAL GEOGRAPHY. 
[part ii r. 
known. Buli minus, Stenogyra, and Pupa are characteristic 
genera. 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, Lithidion, found in Madagascar, Socotra, 
and Arabia. None of the genera appear to be well represented 
throughout the region, and they 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 peculiar 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. 
I. The East African Sub- region, 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 of 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 Yerd, 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 
