XII WEST AND SOUTH AFRICAN SUB-REGIONS 367 



spread of many In do-Pacific species almost as far south as the 

 Cape. Owing to its extreme unhealthiness, and the absence of 

 harbours, the sub-region is very little known. 



The principal genera are Cymhium^ Pleurotoma^ Marginella^ 

 Terehra^ Mitra^ Agaronia^ Murex, Cancellaria^ Purpura^ Pseud- 

 oliva, Natica^ Tellina^ Lucina^ Tugonia^ Schizodesma^ and Area. 

 Studer has enumerated as many as 55 species common to West 

 Africa and the opposite American shores. The north and south 

 equatorial currents, which circulate in this part of the Atlantic, 

 probably transport the larvae from one coast to the other. Pur- 

 pura eoronata Lam., a characteristic West African species, is 

 represented by a well-marked variety in Demerara. 



The Mollusca of St. Helena (178 known species) most 

 resemble those of the West Indies, 50 per cent being common, 

 while 30 per cent are common to the Mediterranean. From 

 Ascension Island only 33 species are known, which in their 

 general relations resemble those of St. Helena.^ 



(6) The South African Sub-region extends along the coast 

 from about lat. 30° on the west, to about East London on the 

 east. Mr. G. B. Sowerby enumerates 740 species from ' South 

 Africa,' but includes in this list Natal species, which more prop- 

 erly belong to the Indo-Pacific fauna. Of these 740, 323 are 

 peculiar, while 67 also occur in European seas, some being 

 familiar on our own shores. It is remarkable to find in a sub- 

 region separated from ourselves by the whole width of the tropics, 

 such well-known forms a3 Mangilia costata Don., M. septangularis 

 Mont., Cylichna eylindracea Penn., Pholas dactylus L., Solen 

 marginatus Pult., Cultellus pellucidus Penn., Ceratisolen legumen 

 L., Lutraria oblonga Chem., Tellina fabula Gmel., T. tenuis Da C, 

 Modiolaria discors L., and many others. 



The leading genera are Uuthria, Triton^ Cominella, Bullia^ 

 .Nassa^ Cypraeovula^ Oxystele^ Fissurella, Fissurellidaea^ Patella^ 

 and Chiton. 



The Mollusca of Kerguelen Island and the Marion and 

 Crozets groups show relationship partly with South America, 

 partly with the Cape, and partly with South Australia and New 

 Zealand, thus showing some trace of a circumpolar antarctic 

 fauna corresponding to, but not nearly so well marked as that of 

 the circumpolar arctic sub-region. Among the remarkable forms 



1 E. A. Smith, P. Z. S. 1890, pp. 247, 317. 



