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Show 1891.] MR. E. A. SMITH ON SHELLS FROM ADEN. 391 use to those who possess shells from this locality and are desirous identifying them. Before concluding these prefatory remarks I have some observations to make respecting the list of species which, according to Mr. Cooke, are " common to the Mediterranean and the Red Sea " \ Examples of the seventeen species he enumerates were collected in the Gulf of Suez by the late Robert Mac Andrew in the early part of the year 1869, some months before the opening of the Canal. It is important to note this as showing that their establishment in the Red Sea was not of recent date. Before expressing any opinion with regard to the accuracy of some of Mr. Cooke's identifications, it was necessary for me to study the specimens themselves, and consequently I applied to Dr. Sharp of the Cambridge Museum, where the Mac- Andrew collection is preserved, and I have to acknowledge his kindness in forwarding all the specimens I required, and I have also to thank Mr. Cooke for kindly looking them out for transmission. The following is the result of my examination :- 1. CERITHIUM (PIRENELLA) MAMMILLATUM, Risso. (= caillaudi, Pot. & Mich.) Nearly all the Suez specimens, which may be referred to a strongly marked variety of this species, have a peculiar facies. They have two distinct rows of granules on the upper whorls, whereas in Mediterranean specimens there are mostly three or more, and in these the granules are smaller than in the Red-Sea specimens. In the Museum we have three specimens from Bombay 2 which are more like the Mediterranean form than that from Suez. In discussing the marine fauna of any particular sea, it is hardly correct to include the genera Cerithidea and Leuconia, the former an estuarine form and the latter an amphibious Pulmonate. Now the distribution of some of these estuarine species is most remarkable, and so unaccountable, that I think the occurrence of two forms in some parts of the Mediterranean and the Bed Sea hardly bears upon the subject of distribution in question. An instance of this unaccountable distribution has lately come to m y notice which may fittingly be recorded here : I refer to Neritina crepidularia. This unmistakable species is known from the mouth of the Ganges, from Pondicherry, Tranquebar, Ceylon, Mergui, Singapore, the Dutch Indian Islands, Philippines, Japan, Persian Gulf, and lastly from the Gold Coast, West Africa, where living specimens were collected by Mr. R. Austen Freeman and presented to the British Museum. 2. EMARGINULA ELONGATA, Costa. The specimen kindly sent me for inspection I certainly consider distinct from the above species. It bears a close resemblance to it in general appearance, and without close examination one would not 1 Ann. Mag. Nat. Hist. 1886, vol. xviii. p. 394. 2 Cerithidea bombayana, Sowerby, Con. Icon. sp. 24. Badly described and figured. |