330 



CENTRAL AFRICAN SUB-REGION 



CHAP. 



Fig. 217. — Columna 

 flamriiea Miill., 

 Princes I. 



not yet been well explored. Tomostele, a genus allied to Strep- 

 tostele, is peculiar, and P seudachatina attains its maximum. 



St. Thomas and Princes Is.^ in the Gulf of 

 Guinea, are well known. Princes I. has 22 

 species, 14 peculiar, and 2 common to St. Thomas 

 only, one of the latter being the great sinistral 

 Acliatina hicarinata Chem. The remarkable 

 genus Colurtuia (Fig. 217) is peculiar, and 

 Streptostele (4 sp.) attains its maximum. Pecul- 

 iar to St. Thomas are Pi/rgina, a turreted form 

 of Stenogyra ; Thyropliorella^ a sinistral form of 

 Zonites ; and Atojyocochlis., a large bulimoid 

 shell, whose true relationships are not yet 

 known. Homorus, a group of Acliatina with an 

 elongated spire, occurring also in the Angola 

 District and on the east coast, has 4 species. 

 No fresh-water species have as yet been dis- 

 covered in either of the islands. 



The Angola and Benguela District^ extend- 

 ing from the Congo to the Cunene R., probably belongs to the 

 West African Sub-region, but until its fauna is better known 

 it is advisable to consider it apart. Acliatina continues abun- 

 dant, but the other characteristic West African forms QPseiida- 

 chatina^ Strep>tostele^ Perideris^ diminish or are absent altogether. 

 No Helix and only 1 Cyclophoriis occur. 



Ovampo^ Damara^ and Great Namaqnaland^ lyiiig between 

 the Cumene and Orange rivers, seem to form a transition district 

 between the West and South African faunas. Helix reappears, 

 while the characteristic West African genera are almost entirely 

 wanting. 



(c) The East African Province extends from about Delagoa 

 Bay to the Abyssinian shores of the Red Sea. In general out- 

 line the province consists of a flat marshy district, extending 

 inland for many miles from the sea ; this is succeeded by rising 

 ground, which eventually becomes a high table-land, often 

 desolate and arid, whose line of slope lies parallel to the trend of 

 the coast. The Mollusca are little known, and have only been 

 studied in isolated districts, usually from the discoveries of 

 exploring expeditions. . 



The Mozambique District., from Delagoa Bay to Cape Delgado, 



