255 

 SOME REMARKS ON THE CAPE MARINE PROVINCE. 



By [. R. LE B. TOM LIN, M.A., F.E.S. 



(Presidential Address delivered at the Annual Meeting, October istli, 1921). 



The coast of what is now the Union of South Africa stretches roughly 

 for some two thousand nine hundred miles between its Portuguese 

 neighbours on the east and west. It will probably be found eventu- 

 ally that as a zoological province its limits tally pretty closely with its 

 political frontiers, and I propose in this address to put some details 

 together which bear on these limits as far as the mollusca are con- 

 cerned. 



Owing to geographical position the marine fauna of the Cape is 

 more than usually interesting and the influence of currents more than 

 usually important. On the eastern side the Mozambique and Agulhas 

 currents bring a fairly plentiful admixture of well-known tropical 

 shells from the Indian Ocean down the coasts of Zululand and Natal 

 — of Conns such as lividus and hebmiis, of Strombus such zs,gibberulus, 

 of Cyprxa such as lynx and erosa, of Nerita such as polita and 

 albkilla, and of bivalves such as Cardita variegata and Tapes textrix. 

 Probably Durban is pretty nearly the farthest limit of these invaders. 

 In this connexion, I may mention that Cypnea tigris was taken alive 

 for the first time in South African waters at Scottburgh, three years 

 ago. So many species are known from this province only in a dead 

 or more or less worn condition that it is extremely hard to determine 

 what part ballast plays in the introduction of novelties. It is certainly 

 a factor which must not be overlooked. 



On the western or Atlantic side flows the comparatively cold 

 Benguela Current, which, after sweeping eastwards from South America 

 as the South Atlantic Current, reaches the African shores in the neigh- 

 bourhood of the Cape Peninsula and washes up the west coast 

 towards the equator. It again crosses the ocean, this time westwards, 

 and bifurcates off" South America, part following the north coast to 

 the West Indies as the South Equatorial Current, and part flowing 

 southwards from Cape S. Roque as the Brazil Current, thus effec- 

 tually preventing the transference of mollusca or indeed of any pelagic 

 life from the West Indies to South Africa. The occurrence of a 

 number of West Indian shells in and about the Gulf of Guinea is due 

 to a counter current, which runs eastward in the neighbourhood of 

 the equator, between the cyclonic systems of the North and South 

 Atlantic. At a certain time of year when the sun is well south of the 

 line the whole systciUi shifts further south, and the Benguela Current 

 then impinges on S. Helena, which for the greater part of the year is 



