XI QUESTION OF A NEANTARCTIC CONTINENT 359 



which the Mollusca may offer evidence. Yon Ihering holds that 

 an essential difference can be observed between certain of the 

 Unionidae wliich iidiabit S. America, Africa, and Australia with 

 New Zealand, and those which inhabit Europe, Asia, and N. 

 America, l)ut the point can hardly be regarded as definitely 

 established at present. Something perhaps may be made of the 

 distribution of Bidimus and Bulimuhis. It seems difficult to 

 explain the occurrence of sul)-fossil Bvlimus on St. Helena except 

 on some such lines as have Ijeen recently adduced to account for 

 tlie presence of struthious birds in the Mascarenes, and possildy 

 the form Livinhacea may be a trace of the same element in S. 

 Africa. Again, the Tjipanis of S. and AV. Australia, with the 

 Caryodes of Tasmania, and the Leucotaenia and Clavator of 

 Madagascar (which all may be related to Bulimus), together with 

 the Placostylvfi of New Caledonia and the adjacent islands, 



Fig. 237. — Macrocydis 

 laxata Fur., Chili. 



reaching even to New Zealand, and perhaps even the Amj^Mdromvs 

 of Malaysia (which are more akin to Bulitnulus), may be thought 

 to exhibit, in some remote degree, traces of a connnon ancestry. 



The land operculates give no help, and, of the carnivorous 

 genera, Rhytida is a marked link lietween Africa and Australia, 

 while ^treptaxis is equally so between S. America and Africa. 

 As regards fresh-water Gasteropoda, Ampidlaria is common to S. 

 America and Africa, while Isidora is common to Africa, Australia, 

 and New Zealand, but is altogether absent from S. America. 

 Gnndlacliia occurs in Florida, Trinidad, and Tasmania, l)ut has 

 not been detected in ^Vfrica. It must be concluded, therefore, 

 that the present state of the evidence which the ]\follusca can 

 afford, while exhibiting certain curious points of relationship l)c- 

 tween the three regions in question, is insufficient to warrant 

 any decided conclusion. 



