694 THE LAND MOLLUSCAN FAUNA OF BRITISH NEW GUINEA, 



One of the most remarkable facts yielded by an analysis of the 

 Australian land molluscan fauna is that the operculate snails are 

 confined to a narrow strip of land along the Queensland coast. 

 Proceeding southwards from Torres Straits, they diminish gradu- 

 ally till the last outpost of the invading army is reached about 

 the Clarence River.* The sole apparent exception to this rule is 

 Truncatella, which spreads to Tasmania and South Australia ; 

 but as this genus is strictly littoral and evidently migrates not 

 by land but by sea, it cannot be considered as a disturbing 

 factor in my generalisation. Contrasting the fauna of Queensland 

 with the more typically Australian and probably archaic fauna of 

 Tasmania, Victoria and Western Australia on the one side, and 

 that of New Guinea on the other, it will be seen that this foreign 

 aspect of the operculate genera Pupina, Helicina and Diplomma- 

 tina is shared by the inoperculate forms of Atopos, Iladra, Chloritis 

 and Papuina; A. prismaticus of Papua claiming affinity with 

 A. australis of Queensland ; H. broadbenti with H. informis ; C. 

 chloritoides with C. porleri ; and P. naso with P. macgillivrayi. 

 The species actually common to both regions are few; B. macleayi 

 inhabits both countries, T, annula only finds a place in the 

 Queensland catalogue! by courtesy, while P. pedicula, S. gracilis, 

 T. ceylanica, T. valida, and L. vitreum are widespread throughout 

 Polynesia. From these premises it may be deduced that the 

 Queensland mollusc fauna, though isolated sufficiently long to 

 have lost specific identity with that of Papua, has nevertheless 

 been derived from it. 



The shallow sea of Torres Straits now severs this continent 

 from the adjoining island. Were its bed raised but seven fathoms, 

 the two countries would be united, while an elevation of ten 

 fathoms would form a wide bridge between them. When the 

 marine life east and west of Torres Straits is better known, it 

 will be of interest to observe whether the influence of an ancient 



* The furthest straggler, so Mr. Brazier informs me, is Helicina jana, 

 Cox, from Port Macquarie, N.S.W. 



f Proc. Roy. Soc. Queensland, vol. v., p. 52. 



