South- African Land-Mullusca. 125 



this curious similarity. Tlie Peltatiiia' in the former country 

 hoKl the same position the Ariophantinje do in tlie latter. 



The remarkable variation in anatomical detail met with in 

 the species of this subfamily has, I suggest, some relation to 

 the very great extent of country over wliicli they are dis- 

 tributed, and still further to be accounted for by the extremely 

 long isolation each species has probably undergone in its own 

 particular habitat. 



The physical nature of the country and the great distances 

 across liigh, arid, treeless tracts point to this, and isohite 

 more widely than usual the localities from which the animals 

 described in this paper have been received. A glance at the 

 map of South Africa will show this more clearly. Thus 

 from Cape Town north-east to Pretoria is 800 miles, from 

 Cape Town eastward to Port Elizabeth is some 400 miles, 

 and another 4:25 or so on to Natal with Durban and Maritz- 

 burg, while from this last place to Pretoria is over 300 miles. 

 JVlost of the intermediate country between these localities 

 does not appear to be of a climatic nature conducive to 

 the rapid extension of mollusks of this kind possessing 

 extensible lobes to cover the shell ; their habits and require- 

 ments necessitate a considerable amount of moisture. They 

 could only unrestrictedly move along the lines of main 

 drainage or the more wooded jungle-clad slopes of the lateral 

 ranges. 



Species very similar in shell-characters are found far 

 beyond the area I have above indicated, many of which 

 I have noticed in the Natural History Museum, but as the 

 animals of these species are not yet known they can only 

 be placed provisionally in the Peltatin^e. 



further north, in Africa and in Abyssinia, we know that 

 Helicarion-Vike shells of the family Zonatida? occur, repre- 

 sented by the genus Africarion, type i^M^us or lympliaceus, 

 JMorelet, described by me in the ^Mollusca of India,"* vol. i. 

 })p. 154-158, pi. xlii. As we obtain further malacological 

 knowledge of these species, their true geographical distri- 

 bution and limits of range and their relationshij) will be 

 of extreme interest. 



Even while preparing this paper, my attention has been 

 called to a very excellent, valuable contribution to our 

 knowledge of African land-shells by Professor Dr. J. 

 T'hiele, entitled ' Mollusken der Deutschen Zentralafrika- 

 Expedition,' 1907-1908. This expedition, under the leader- 

 ship of Adolf ¥. Herzog zu Mecklenburg, has been productive 

 of good work, and Professor Thiele describes a large number 

 of new species in many genera. Some eight species are re- 



