66 PERCY SLADEN TRUST EXPEDITION. 



from P. Pischer's ' Manuel de Conchyliologie,' of which comprehensive work, published 

 in 1887, a new edition is beginning to be much wanted. 



A brief bibliographical resume is given at the end of this paper. 



I would wish, in conclusion, to express my sense of Mr. Edgar Smith's kindness 

 in providing every facility for the necessary comparisons of certain species with their 

 accredited types at the British Museum (Natural History), and for his personal aid 

 in the matter. I would also thank Mr. Stanley Gardiner, F.R.S., for having given me 

 the opportunity to study a particularly interesting Fauna. 



Comparntive Distribution of 470 Species of Mollusca recorded in Ten Subdivisions 



of the Indo-Pacific Region. 



No. of 

 Species, 

 (i.) South and S.E. Africa, comprising the Cape of Good Hoi)e to Natal, and 



northward to Portuguese E. Africa 184 



(ii.) Mauritius, Bourbon, Rodriguez, and Madagascar 312 



(iii.) Laccadive and Maldive Archipelago 169 



(iv.) Red Sea and Aden 151 



(v.) Persian Gulf, Gulf of Oman, and North Arabian Sea, including Bombay to 



Panjim and Goa 139 



(vi.) Ceylon, with S. Hindostan, and Madras Coast 198 



(vii.) Andaman Is., Bay of Bengal, Malaya, Sumatra, &c 158 



(viii.) Philippine Isles 287 



(ix.) Polynesia, including E. New Guinea and N.E. Australia 229 



(x.) Japan and Loo Choo Isles 185 



It is natural that the closest affinity should exist with (ii.), which heads the list 

 with 312 species in common, but more curious that the Philippine Region (viii.) should 

 come next in order, with 287. This district, however, has been unu.sually well worked, 

 and no doubt when (vi.) and (vii.) receive an equal amount of attention the numbers 

 will be proportionately considerably augmented. It will be observed that (iv.) and (v.), 

 embracing the northernmost portions of the Arabian Sea, the Red Sea, and the Persian 

 Gulf, show the smallest ratio of community of species ; and of these, the last-named, 

 with the Gulf of Oman, has been very fully examined during the past ten or fifteen 

 years, a total of 1620 species having been catalogued. It is therefore somewhat 

 surprising to find that, so far as can be estimated with our present knowledge, but 

 a twelfth part of these descend so far south as the Seychelles, Amirantes, or Chagos 

 Archipelago 



