THE CARNIVOROUS SLUGS 01*^ SOUTH AFRICA. 253 



ti nidge Avhen this family was scarcely distinct from the 

 Megaspi ridge. Nevertheless, until further anatomical 

 investigations have been made, it is impossible to say exactly 

 to which group now living the 01eacinida3 are probably 

 most nearly related. 



It is equally difficult to form an opinion as to the place 

 of oi'igin of the family, for both the Ac ha tin idee and 

 the Megaspiridge have an extremely wide distribution. 

 Perhaps the Oleacinidse may have arisen near the southern 

 or south-eastern shores of that continent which geologists 

 believe to have stretched from Western Europe to America 

 during a lai'ge part of the Mesozoic era. If this were the 

 case, the south-eastern expansion of the area of distribution 

 would be prevented by the extensive " Mediterranean Sea " 

 which then existed ; the gradual growth of the North Atlantic 

 would separate the European from the American forms, and 

 the subsequent incoming of the Glacial Period would restrict 

 the northern distribution of the family. On the other hand, 

 the Oleaci nidge may possibly have arisen further south, 

 and have entered America by way of the old land-connection 

 which probably extended from Africa to Brazil. The absence 

 of the Oleacinidas from the Ethiopian Region is a possible 

 objection to this theory ; but perhaps the family may have 

 once extended into that area, and may have there been 

 exterminated by the elongate Streptaxida3 — Ennea, 

 St reptostele, and their allies — which would probably enter 

 into competition with them, but appear to have arisen just 

 too late to follow the heliciforni Streptaxidse across to the 

 Neotropical Region. The limited distribution of the Olea- 

 cinid« in South America is, however, another objection to 

 the theory of their southern origin, and the first view that I 

 have given seems to me to be the more probable. lam there- 

 fore glad to see that Pilsbry now upholds the more northerly 

 origin of the family,^ although seven years ago he thought 

 that the probabilities favoured the hypothesis that the Olea- 



1 ' Rep. Princeton Univ. Exped. Patagonia 1896-1899,' vol. ill, Zool., 

 1911, p. 625. 



