EASTERN AFRICA THE GREAT LAKES 



331 



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

 Cyclostoma (2 sp.) TrocJionanina (4 sp.), Urocyclus, a character- 

 istic African shig (2 sp.), Rachis (6 sp.), Fachnodus (2 sp.), and 

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



Fig. 218. — Urocyclus coviorensis 

 Fiscli., Comoro Is. : G, Gen- 

 erative oritice ; M, mucus 

 gland ; 0, oiitice leading to 

 internal sliell ; P, pulmonary 

 orifice ; T, tentacles. (After 

 Fischer. I 



The Zanzibar iJlsfrict, from Cape Delgado to the Somali 

 country, has the same general featm-es. Meladovms, a large 

 sinistral AmjmUaria, is characteristic, while Cyclostoma (5 sp.) 

 becomes more abundant. Hdix 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 Otopoina type {Georgia, Rochehrunia, Revoilia) whose generic 

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

 plants Rachis and PacJinodus. Achatina is nearly wanting, 

 \)\\t Limicolaria has 9 species. A few Helix, said to l)e of the 

 Pisana group, occur. 



The District hetiueen the Great Lakes and the coast region is 

 fairly well known through recent explorations, especially those 

 associated witli 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 

 B'uliminus, Cerastus, and Hapalus replace, to some extent, the 

 Achatina and Limicolaria of the marshy plains. Land oper- 

 culates iCyclophoriiS 1, Cyclostoma 8) are more numerous ; among 

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

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

 of a Littorina. The characteristic African bivalves {Matela, 

 Spiatha, etc.), are few in numljer. 



{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 (Oukerewe, 3700 ft.), 

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

 and su]i])ly an interesting problem in distribution. Those of the 



