248 MR. E. A. SMITH ON THE [A-Pf- '' 



washed ashore on the windward or south side of the island. These 

 specimens will be enumerated in an Ap[)endix, as they cannot be 

 regarded as belonging to the St. Helena fauna. In nearly every instance 

 in which it has been possible to associate them with known species, 

 they prove to be South-African forms, thus clearly showing that 

 they have been drifted northwards from the Cape by the prevailing 

 south-east trade-winds and oceanic currents. 



Capt. Turton observes in his notes that some of them were 

 alive when taken, and this was generally the case when the " Sea- 

 horn " was only recently washed up, or was secured from a boat. 

 Notwithstanding this fact, it is remarkable that scarcely any 

 {exclusively^ South-African species apjjear to survive and become 

 established at St. Helena; indeed, Gadinia costata is the only 

 species in this collection, not found on " Sea-horn," the distribution 

 of which has hitherto been restricted ro South Africa. A few species 

 such as Triton olearium, Triforis perversa, Cingulina circiiiata, 

 Saxicava arctica, Mytilus edulis, M. magellanicus, Area domingensis. 

 Pinna pernvla, and perhaps one or two others, are found at both 

 localities, but they mostly have a wide distribution. 



As it is seen that many species are drifted from the Cape to 

 St. Helena, the question arises whether some of those dredged by 

 Capt. Turton, or found by him and others upon the shore, may not 

 have become detached from the floating seaweed. 



In one or two cases it is pretty certain that this has occurred, as 

 specimens of Mytilus magellanicus and M. edulis (?) were obtained 

 alive attached to floating weed and also dead upon the shore. Two 

 dead specimens of Patella compressa, a well-known Cape species, 

 were also collected on the shore, there being every probability of 

 their having been carried there attached to seaweed. 



The molluscan fauna of St. Helena appears most to resemble that 

 of the West Indies ; for, of the known species ^ in this collection, 

 just fifty per cent, are common to the two localities. 



About five-and-twenty species, or thirty per cent., are identical 

 with Mediterranean forms, and about half a dozen occur at all three 

 localities. About thirteen species are also met with on the West- 

 African Coast, between the Gulf of Guinea and Morocco. 



What proportion of species are common to St. Helena and the 

 west coast of Africa, south of Guinea, it is difficult to ascertain 

 at present, as comparatively little is known of the Mollusca of that 

 part of the coast. 



However, in Bunker's list of shells from Lower Guinea, eight 

 species are quoted which are common to St. Helena. The similarity 

 between the fauna of St. Helena and that of the West Indies is 

 undoubtedly, in a great measure, due to oceanic currents. 



According to various maps an important current flows from near 

 the centre of the South Atlantic past Ascension Island along the 

 north coast of South America to the West Indies, a return current 

 passing in an easterly or south-easterly direction towards the Gulf 

 of Guinea. These and the great Gulf-stream in all probability have 

 ^ Pelagic forms are not included. 



