292 NORTHERN AFRICA AND THE SAHARA chap. 



macella are represented by a single species each, and there is one 

 Clausilia. According to Kobelt/ the original land connexion 

 between southern Spain and Morocco must have been much 

 more extensive than is usually assumed, and probably reached at 

 least to the meridian of Oran and Cartagena, The Mollusca of 

 Oran and Cartagena are, according to him, much more closely 

 related than those of Oran and Tangier, or those of Cartagena 

 and Gibraltar, but at Cartagena some species, which are charac- 

 teristic of the Mediterranean coasts from Syria westward, dis- 

 appear, are absent from the rest of Spain and from Morocco, 

 but reappear on the south-western coasts of France. These 

 species may possibly Ivdva pushed along that arm of the sea 

 wliich, when the Straits of Gibraltar were closed as far as the 

 latitude of Oran and Cartagena, united in comparatively recent 

 times the Bay of Biscay with the Gulf of Lions. 



The following genera, which do not occur in Spain, have 

 prol)ably spread into northern Africa as far as Algeria, via 

 Sicily and Tunis, namely, Glandina (1 sp.), Daudebardia (1 

 sp.), Fomatias (2 sp.). Tunis shows strong traces of Sicilian 

 influence, and Kobelt found a colony of snails, of Sicilian ahini- 

 ties, as far west as Tetuan. 



The Sahara. — The Algerian Sahara contains, in many places, 

 a sub-fossil Molluscan fauna which appears to show that the 

 district has, in quite recent times, undergone a gradual desicca- 

 tion. The species are mainly fresh-water, including Melania, 

 Melanupsis, and Corhicida, with here and there valves of Cardium 

 edide, and indicate, on the whole, an affinity with recent Egyptian, 



rather than North African species. 

 It is probable that a vast series 

 of ^tangs, or brackish-water lakes, 

 <iuce stretched along this region, 

 ami were ultimately connected 

 with the sea somewhere between 

 A ^ Tunis and Egypt. 



Fig. 195. — Characteristic shells of S. ^-.n (-y ,-, T7r„„_„^ TKr. 



Yv^o^: K,Heiix{Maadaria),ddensis (n) Southern France.— ThQ 



Fer. ; B, Leucochroa candidissima southern portion of France 



^^''''^^" bordering on the Mediterranean 



contains many species, especially of Helix, which do not occur in 

 the centre and north. Amongst these are — 



1 Jahrl. Dcutsch. Malak. GescU. viii. p. 278. 



