XI 



SOUTHERN ARABIA — SOUTH AFRICA 



333 



Arabia the mixture of types produces curious results : the Helix^ 

 Clausilia^ and Vitrina being Palaearctic, the Limicolaria and 

 all the operculates Ethiopian, while the single Trochomorpha 

 is Indian. Indian influence, indeed, comes out unmistakably 



Fig. 219.— Tiphobia Horei E. A. Smith, 

 L. Tanganyika. 



Fig. 220. — Mollusca charac- 

 teristic of L. Tanganyika : A, 

 Nassopsis nassa Woodw. ; 



B, Spekia zonata "Woodw. ; 



C, Syrnolopsis lacustris E. 

 A. Smith. 



throughout the province. Thus in Socotra there are two Cyclo- 

 topsis^ in Abyssinia two Africarion (closely related to the Indian 

 Girasia'), two Microcystis^ and a Grlessula, and in the Scioa dis- 

 trict there is a Sitala. The fresh-water Mollusca of Socotra are 

 Indian forms. 



(2) The South African Sub-region. — The principal charac- 

 teristic of the Mollusca of S. Africa is 

 the occurrence of numerous small species 

 of Helicidae, belonging chiefly to the 

 groups Pella^ Phasis, Dorcasia, and 

 Sculptaria^ all of which are practically 

 peculiar. Carnivorous genera are also 

 prominent, Ennea here attaining its 

 maximum. RTiytida (to which several 

 species still regarded as Pella belong) is 

 common only to the S. Pacific and Aus- 

 tralasia, and forms, with Isidora among 

 the fresh-water pulmonates, a remarkable 

 link of connexion. Aerope^ the largest 

 of all helicoid carnivorous genera, and 

 ChlamydepJiorus^ a carnivorous slug with 

 an internal shell, are peculiar. Achatina 

 is still abundant, but Limicolaria is wanting. Livinhacea, a 



Fig. 221. — Achatina zebra 

 Lam., S. Africa. X §. 



