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Show 1890.] ON THE MARINE MOLLUSCA OF ASCENSION ISLAND. 317 Fig. 20. Cylichna remissa, p. 312. 21. Turbo (Collinia) incertics, p. 311. 21 a. ( ) ; upper view. 22. Scissurella jucunda, p. 311. 22 a. ; upper surface. 23. Kellia crassiuscula, p. 313. 24. • atlantica, p. 313. 25. Montacuta subtriangularis, p. 313. 26. Crenella pura, p. 314. 4. On the Marine Mollusca of Ascension Island. By EDGAR A. SMITH. [Received March 14, 1890.] In the following list of forty-two species of Mollusca from Ascension Island, nine, obtained by the 'Challenger' Expedition, ought not perhaps to be included in the fauna ; for, altbough dredged close to the island off the west coast, they were from a depth of 420 fathoms. The poverty of this list is doubtless due to the fact that no experienced collector has ever explored the shores. Fourteen cf these species occur at St. Helena, eleven are West- African, twelve are found at the Cape Verde, Canary Islands, and the Azores, nine are Mediterranean, and seventeen, or about 40 per cent., are West-Indian forms. These figures, on comparison with those referring to the species found at St. Helena, and given in the previous report, show that the relationship of the two faunas to other regions is the same. Both resemble that of the West Indies more than any other locality, both have a considerable percentage cf species common to West Africa, to the Atlantic Islands, including the Cape Verdes, Canaries, Madeira, and the Azores, and also to the Mediterranean, the causes which have effected this distribution doubtless being the same in both cases. The three species of Marginella are well-known Cape forms, and therefore the question arises, whether these shells may not have drifted to Ascension on floating tangles as in the case of numerous species at St. Helena. A few species are eastern forms, for example Ostrea cucullata and Malleus regula. Both of these, I believe, are established at Ascension. The former was quoted by Chemnitz more than a hundred years ago, and although he remarks that ships returning from China and the East Indies used to call at Ascension for water, I do not think it likely that the shells were carried there from the east. The single valve received from Dr. Conry is in very fresh condition and has not the appearance of having been rolled on the beach. In the ' Universal Conchologist' Martyn has figured a small specimen of the well-known Fusus proboscidi^erus of Lamarck, under the name of Buccinum incisum, and gives as the locality "Ascension Island, new Guinea." PROC. ZOOL. S O C - 1890, No. XXII. 22 |
