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Show 1881.] ON SHELLS FROM SOCOTRA. 251 9. On the Land Shells of the Island of Socotra collected by Prof. Bayley Balfour. By Lieut-Colonel H. H. GODWIN-AUSTEN, F.R.S., F.Z.S., &c. Part I. Cyclostomacese. [Received January 18, 1881.] (Plates XXVII., XXVIII.) For the recent exploration of the Island of Socotra we are very greatly indebted to Mr. Sclater, who from the first so strongly advocated the examination of its flora and fauna. This work has been most ably carried out by Prof. Bayley Balfour, who volunteered his services, and who, after a necessarily short stay there of only six weeks in the cold season of 1880, brought away with him a fine store of specimens. The present paper is based on a study of the land- and freshwater Mollusca thus obtained. It is proposed to bring out this list in two parts, instead of waiting until the whole collection has been examined and compared. The first contribution, now submitted, comprises the Cyclostomaceae. As a whole, they are, as might have been expected, African and Arabian in character, the connexion being certainly, as regards the oper-culated forms, more Arabian than African. The collection contains a number of very distinct, fine and interesting forms, of which some were already known, but many are new and considerably extend the list of Socotran species. The large area of limestone formation on the island i3 especially favourable to the existence of these creatures, while island-conditions have, as usual, modified and increased the species of some genera. I hope to be able to show to what extent the species are allied to the adjacent continental forms-always so interesting a point as regards island faunas. The Helicidae number about twenty species, the operculated species ten, while there are some eight freshwater, or a total of about forty. It is remarkable to note that there is not a single true Helix represented in the collection : one specimen I did at first think was a Helix ; but it is in in a very imperfect state, and on further examination appears to belong to the Buliminae. Species of Buliminae are the most numerous among the Helicidae, the greater numbers being allied to Mr. G. Nevill's subgenus Acha-tinelloides, which is closely allied to a group which extends through Arabia and Persia to N.W. India. Of the genus Otopoma, represented in Socotra by six species, there is found in the neighbouring island of Abd-el-Goury O. modestum, Petit, which is not in the collection and appears to be peculiar to that island, as also Cyclostoma gratum, a genus not represented in the collection. It is interesting to note how restricted Otopoma is to Arabia and the islands off the east coast of Africa. The only exceptions are :- O. albicans, Sow., in the British Museum, given as from the island of 17* |