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Show 1890.] MARINE MOLLUSCA OF ST. HELENA. 249 tended to assimilate, to some extent, the faunas of the West Indies and West Africa by transmitting from place to place the pelagic fry of some of the species, and the adult forms and the ova of others attached to floating sea weed. Not more than fourteen species in this collection belong to forms which occur in the Indo-Pacific region. This comparative paucity of species common to these two regions is probably, in a great measure, attributable to the cold Antarctic currents, which, flowing northward to the Cape of Good Hope, bar the emigration of species from the Indian Ocean into the Atlantic. Semper1 refers to the sudden and marked change in the fauna on rounding the Cape, the result of different currents and temperature. The only list of species from St. Helena which has yet appeared is that prepared by Jeffreys3, which was based upon a collection made by Mr. Melliss, who, in his book on St. Helena (pp. 113-128), has reproduced and somewhat amplified it. In this list only forty-one marine species are enumerated, the majority consisting of shells of fairly large dimensions, which, with one exception (Ostrea crista-galli), were all picked up on the shore. This list did not contain all the species which had been previously recorded from the island, at least half a dozen forms being omitted. The large proportion of new species hereafter described, most of them very small, is not therefore altogether surprising, as so little was previously known of this fimna. Thanks to Capt. Turton's energy, as many as 138 additional named species are now added to the list, bringing up the total of known forms to 178. This number, however, does not at all approximate the total of the species which really exist around St. Helena ; for, in addition to those which I have been able to determine, there is a considerable number, nearly a hundred species, which, on account of their immature or bad condition, could not be satisfactorily identified or described. Besides, whenever more extensive dredging is carried on, many additional species will doubtless be discovered 3. A certain number of species have been described from St. Helena which in reality do not inhabit that region. This mistake has arisen from the misspelling of St. Elena on the west coast of America. The species are :-(1) Cancellaria tessellata, Sowerby ; (2) C. obtusa, Kiener (non Deshayes)=C solida, Sow. ; (3) Marginella granum, Kiener = Erato scabriuscula, Gray ; (4) Purpura, undata, Lamarck, partim=P. biseriatis, Blainv.; "(5) Ostrea columbiensis, Hanley; (6) Circe fiuctuata, Sow.; (7) Strombus granulatus, Gray 4. 1 Animal Life, p. 278. 2 Ann. Mag. Nat. Hist. 1872, vol. ix. pp. 262-4. 3 Specimens of Cyprma testudinaria, C. moneta, C. arabica, and Placuna sella were obtained by Capt. Turton as St. Helena shells ; but he shrewdly doubted their genuineness. He observes, " ships from all parts of the world touch here, often bringing shells which are got by the natives, and then offered as island shells." This is evidently the true explanation of the presence of these species at St. Helena. 4 Species 1 to 4 are quoted from Kiener's ' Icon. Coq. Viv.,' and 5, 6, and 7 from Reeve's ' Conch. Icon.' |