(5) =The Chilian Sub-region.=--The greater part of Chili, from its arid and rainless climate, is unfavourable to the existence of land Mollusca. _Bulimus_ (_Borus_) still has 3 or 4 species, and _Bulimulus_ (_Plectostylus_ 11, _Scutalus_ 9, _Peronaeus_ 7) is fairly abundant, but the profusion of the tropics is wanting. There are no carnivorous genera, and only two land operculates. A remarkable form of _Helix_ (_Macrocyclis_, Fig. 237) is quite peculiar, but the majority of the species belong to two rather obscure groups, _Stepsanoda_ and _Amphidoxa_. _Chilina_, a singularly solid form of _Limnaea_ (of which 8 sp., with a sub-genus _Pseudochilina_, occur in Chili), is peculiar to Chili, S. Brazil, and Patagonia. From the two islands of _Juan Fernandez_ and _Masafuera_, are known several _Helix_, of Chilian affinity, several curious _Succinea_, a _Homalonyx_, _Leptinaria_, and _Nothus_, and three species of _Tornatellina_, with the almost universal _Limax gagates_. The question of the existence at some remote period of a Neantarctic continent, which formed a communication between the three great southern peninsulas of the world, is one on which the Mollusca may offer evidence. Von Ihering holds that an essential difference can be observed between certain of the Unionidae which inhabit S. America, Africa, and Australia with New Zealand, and those which inhabit Europe, Asia, and N. America, but the point can hardly be regarded as definitely established at present. Something perhaps may be made of the distribution of _Bulimus_ and _Bulimulus_. It seems difficult to explain the occurrence of sub-fossil _Bulimus_ on St. Helena except on some such lines as have been recently adduced to account for the presence of struthious birds in the Mascarenes, and possibly the form _Livinhacea_ may be a trace of the same element in S. Africa. Again, the _Liparus_ of S. and W. Australia, with the _Caryodes_ of Tasmania, and the _Leucotaenia_ and _Clavator_ of Madagascar (which all may be related to _Bulimus_), together with the _Placostylus_ of New Caledonia and the adjacent islands, reaching even to New Zealand, and perhaps even the _Amphidromus_ of Malaysia (which are more akin to _Bulimulus_), may be thought to exhibit, in some remote degree, traces of a common ancestry.