366 LUSITAINAN SUB-REGION chap. 



north than the southern coasts of the Channel, the west of 

 France, and the Mediterranean. 



The Baltic, a sea specially liable to violent changes of tem- 

 perature, with a large admixture of fresh water at its eastern 

 end, appears to possess only about 65 species in all. More than 

 50 genera occurring on the western coasts of Denmark do not 

 enter the Sound. In the eastern portion of the Baltic marine 

 and fresh-water species live together (p. 12). 



(4) The Lusitanian Sub-region extends from Cape Ushant 

 in the north to Cape Juby (lat. 28°) in the south, and includes 

 the whole of the Mediterranean, as well as the Azores, Canaries, 

 and Madeira groups. 



The English Channel acts as an effectual barrier to the 

 northward extension of many species ; as many as 81 species 

 which occur in western France do not reach British coasts 

 (P. Fischer). At the same time, the western coasts of France 

 are rather intermediate between the two sub-regions than 

 distinctly Lusitanian, for between 50 and 60 Mediterranean 

 genera do not occur on those coasts. 



The Mediterranean itself is exceedingly rich in species, about 

 1200 in all (including deep-water species) being known. A 

 certain number of these belong to tropical genera which here 

 find their northern limit, e.g. Fasciolaria, Cancellaria, Sigai-etus^ 

 Siliquaria^ Cliama^ Spondylus. Here too occur Carinaria, 

 Lohigei\ Oxynoe^ Peclicularia^ Cypraea^ Marginella^ Mitra^ DoUum, 

 Cassis^ Cassidaria, Pisania^ Euthria^ Vei^metus^ Argonauta^ and 

 many others. A few Celtic and even Boreal species, which occur 

 on the western coasts of Morocco, do not enter the Mediterranean. 

 Among these are Purpwa lapillus^ Helcion pellucidum^ and 

 Tellina balthica. Halia, a rare West African genus akin to 

 Pleurotoina^ is found in Cadiz Bay, and the West African Cym- 

 hium occurs on the Spanish coasts as far as Malaga. 



The Black Sea, whose northern and v/estern coasts are 

 exceedingly cold, is comparatively poor in species. The Sea of 

 Azof is chiefly characterised by forms of Cardium. 



(5) The West African Sub-region extends from Cape Juby to 

 a point probably not very far south of lat. 30° S., the cold cur- 

 rent which sweeps up from the Pole probably limiting the south- 

 ward extension of tropical species on this side of Africa, while 

 the warm Mozambique current on the eastern side permits the 



