XI EASTERN AFRICA — THE GREAT LAKES 33 1 



includes no genus which does not occur on the west coast, 

 except Cyclostoma (2 sp.). Trochonanina (4 sp.), Urocyelus^ a 

 characteristic African slug (2 sp.), Rachis (6 sp.), Pachnodus 

 (2 sp.), and Achatina (5 sp.), are the principal groups. 



Fig. 218. — Urocyclns comorensis 

 Fisch., Comoro Is.: G, Gen- 

 erative orifice; M, mucous 

 gland ; 0, orifice leading to 

 internal shell ; P, pulmonary- 

 orifice ; T, tentacles. (After 

 Fischer.) 



The Zanzibar District^ from Cape Delgado to the Somali 

 country, has the same general features. Meladomus, a large 

 sinistral Ampullaria^ is characteristic, while Cyclostoma (5 sp.) 

 becomes more abundant. Helix is still absent, but the carnivor- 

 ous forms (^Streptaxis 2 sp., Ennea 7 sp.) are rather numerous. 



The Somali District is characterised by operculate groups of 

 the Otopoma type ( G-eorgia^ Rochehrunia^ Revoilia) whose generic 

 value is rather doubtful. Petraeus, in an Arabian type, sup- 

 plants Rachis and Pachfiodus. Achatina is nearly wanting, but 

 Limicolaria has 9 species. A few Helix, said to be of the Pisana 

 group, occur. 



The District between the Great Lakes and the coast region is 

 fairly well known through recent explorations, especially those 

 associated with Emin Pasha. Streptaxis (6 sp.) and Ennea 

 (24 sp.) are numerous. Helix is wanting, and the Naninidae 

 are represented by Trochonanina (7 sp.), and other forms at 

 present grouped under Nanina or Hyalinia. On the high ground 

 Buliminus, Oerastus, and Hapalus replace, to some extent, the 

 Achatina and Limicolaria of the marshy plains. Land oper- 

 culates (Cyclophorus 1, Cyclostoma 8) are more numerous; among 

 fresh-water genera we have Lanistes (5 sp.), Cleopatra (3 sp.), 

 Meladomus (1 sp.), and Leroya, a sinistral form with the facies 

 of a Littorina. The characteristic African bivalves (^Mutela, 

 Spatha^ etc.) are few in number. 



(d) Province of the Great Lakes. — The Mollusca of the four 

 great lakes of Eastern Central Africa — Lakes Albert Nyanza 

 (Luta Nzige, 2720 ft.), Victoria Nyanza (Ouk^r^w^, 3700 ft.), 

 Nyassa (1520 ft.), and Tanganyika (2800 ft.) — are well known, 

 and supply an interesting problem in distribution. Those of the 



