292 NORTHERN AFRICA AND THE SAHARA chap. 



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

 Qlausilia. 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 have pushed along that arm of the sea which, 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 

 probably spread into northern Africa as far as Algeria, via Sicily 

 and Tunis, namely, Grlandina (1 sp.), Baudehardia (1 sp.), 

 Pomatias (2 sp.). Tunis shows strong traces of Sicilian influ- 

 ence, and Kobelt found a colony of snails, of Sicilian affinities, 

 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^ 

 Melanopsis^ and Oorhicula., with here and there valves of Cardium 

 edule^ and indicate, on the whole, an affinity with recent Egyp- 

 tian, rather than North African 

 species. It is probable that a vast 

 series of etangs., or brackish- water 

 lakes, once stretched along this 

 region, and were ultimately con- 

 nected with the sea somewhere 

 A B between Tunis and Egypt. 



Fig 195. -Characteristic shells of S. q^^ Southern France, — T\iQ 



France: A, Helix (Macularia) m- ^ -^ 



ciensls Fer. ; B, Leucochroa candi- SOUthem portion of France bor- 



dmmaDrap. dering on the Mediterranean 



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

 the centre and north. Amongst these are — 



1 Jahrb. Deutsch. Malak. Gesell. viii. p. 278. 



^ 



