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. 



[Eeceived January 18, 1881.] 

 (Plates XXVIL, XXVIIL) 



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, bat many are new and considerably extend the 

 list of Socotran species. The large area of limestone formation on 

 the island is 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 alUed to the adjacent continental forms — always so 

 interesting a point as regards island faunas. The Helicidse 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 nHeliv ; but it is in 

 in a very imperfect state, and on further examination appears to 

 belong to the Buliminse. 



Species of Buliminas are the most numerous among the Helicidae, 

 the greater numbers being allied to Mr. G. Nevill's subgenus AcAa- 

 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-Gonry O. mod^stum, 

 Petit, which is not in the collection and appears to be peculiar to 

 that island, as also Cyclostoma gratuin, a genua 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 



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