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Show 398 MR. E. A. SMITH ON SHELLS FROM ADEN. [June 16, The following table also lends some support to this proposition. It will be noticed that, starting from Australia r and the Philippine Islands, all are found in the Red Sea, four at the Cape, one has been recorded from St Helena, one from Ascension, six from the Atlantic Islands, and all in the Mediterranean. Name of species. Chiton siculus Philine aperta Lima inflata Area lactea Australian region. # 0 ... * * * # * 03 CD CD * * * * * * # # e3 * * ... 03 0 <D CD w CO * a p a o * ... • •• CD H o '-J3 # * # # a ee <D c u CD <D # * * * * # # * It is quite possible that most of these species may have been carried across the Indian Ocean2 to the Cape in various states of development, for we know that a very large quantity of pumice thrown into the sea during the eruption of Krakatoa in 1883 was drifted in that direction, indicating the course likely to be taken by larval and pelagic forms or even by adult organisms (like the last five of the above species) if attached by a byssus to, or burrowing into, floating substances like pumice. Passing the Cape they may have extended up the West-African side of the Atlantic past the Atlantic Islands3, and so on into the Mediterranean, at the entrance of which at Gibraltar, the main strong surface current is from the Atlantic eastward, which would of course be favourable to the influx of species from that sea. As I have before stated, this is all mere conjecture, and we have to assume a starting-point somewhere in the East, for which we have no grounds. The proposition that species common to the Red Sea and the Mediterranean may have originated in the East, holds good also in regard to three of the four species which I consider sufficiently different from the Mediterranean species to be regarded as distinct. Even if we consider them practically identical, as Mr. Cooke does, 1 Euthria cornea was recorded from New Caledonia by Brazier in 1889, and the ' Challenger' dredged off Sydney about 10 species of Mollusca which are inseparable from N. Atlantic forms. 2 W e conjecture that the ocean-currents took the same direction in bygone days: what grounds have we for this ? s Vide m y reports on the Mollusca of St. Helena and Ascension Island (P. Z. S. 1890, pp. 247, 317). |