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Show 450 Mil. HARPER PRASE ON POLYNESIAN LAND-SHELLS. [May 2, Ilogoleu. The genus Reyistoma is represented by a single species. All the above East-Indian forms occur on the most westerly islands, which have not been thoroughly explored ; I anticipate that, when searched, they will yield a much larger proportion of Polynesian species, for the reason that these are of small size, and have escaped the notice of inexperienced collectors. Passing south over the Tarawan Islands (Kingsmill), all of which are low atolls, we arrive at the Samoas, the nearest group in Southern Polynesia to the Papuan Islands ; it has yielded but a small number of species, although it has been explored by several persons within the past ten years*; they are all peculiar or of Polynesian types. Going on east to the Tahitian, Hervey, Austral, Paumotus, and Mar-quesan groups, comprising over one half of all the Polynesian islands, we find them inhabited by pure Polynesian forms. The genus Partula here attains to its highest development; also Pitys and other genera of Helicince. All the operculated genera, with the exception of the cosmopolitan genera Helicina and Truncate/ la, are peculiar. The type of Omq)halotro]jis, Pfr., does not extend to this part of Polynesia; but the genus is represented by several peculiar varieties which I have distinguished under the subgeneric names of Scalinel/a, Atropis, and Cyclomorpha. The genus Diadema, Pse., is confined to the Hervey group ; and Chondrella, Pse., is widely spread over the several islands. Two of the genera characteristic of the Polynesian fauna appear to have passed over to the Papuan Islands, viz. Partula and Pitys; of the former, nineteen species have been described from those islands. With one or two exceptions they are of simple bulimiform shape, and may not, at least all, prove to belong to the genus. Thirty-five or more species of Helices have been described from the Papuan Islands, Australia, N e w Zealand, and Tasmania, under the genera Patula, Discus, &c, which are nearly related to the Polynesian genus Pitys. They are generally more planorboid in shape, with the aperture open and not laminate or dentate ; their relation to the genus Pitys cannot be determined until the animals are examined and compared. It appears, therefore, that while a few East-Indian types have entered and extend a short distance into Western Polynesia, as might be expected from their near contact on the south, the Polynesian genera have passed over to the Papuan Islands. The Hawaiian Islands, on the northerly boundary of Polynesia, present several peculiarities in both their marine and land fauna, as might be supposed from their isolated position. Over two thirds of all the land-shells belong to the Helicterince, all of which are confined to that group of islands, as also the genera Carelia and Catinella. The several genera of Helicince are common with Southern Polynesia. The only operculated genus is Helicina; while on the islands of Southern and Western Polynesia no less than sixteen occur. It is also the only locality in which the genera Blauneria, Pedipes, and Ophicardelus of the Melampinse have been discovered. * The Samoan Islands, in proportion to their size, are inhabited by a few more than one quarter of the number of species found at the Tahitian. |