726 ME. R. E. TURNER ON 



It is quite possible that the genus will have to be subdivided 

 owing to dift'erences of structure, especially in the tarsal ungues, 

 which in most of the Australian species have a blunt lobe at the 

 base, but in the African, South American, and a few Austialian 

 species are bifid. The neuration is iso variable, even in the same 

 species, that I do not consider that genera should be founded on 

 the shape of the radial cell alone, on which character the sub- 

 genera Golohosila Sichel and tkdlosila Saussure have been based. 

 In two Australian species the cell is acute at the apex, in others 

 blunt, and African species may similarly be divided into two 

 groups. But until more species are known in both sexes any 

 subdivision would be rash and unnecessary. 



The geographical distribution of the genus is interesting, being 

 almost entirely Southern, including Australia (where the species 

 are most numerous). South America as far north as the Amazon, 

 Madagascar and South Africa spreading up the East African 

 coast to Suakin and crossing to Aden. I am aware that many 

 regard similar cases of distribution as a proof of southern oi'igin, 

 and explain them by former northern extensions of the Southern 

 continent connecting at different times with southern extensions 

 of the land in the Southern Hemisphere. But taking into 

 consideration the enormous depth of the Southern oceans I 

 cannot look on this explanation as satisfactory, and think that it 

 is more reasonable to look on this a,nd other similar cases of 

 distribution as instances of the survival in the south of genei'a 

 which in former times had a much more extensive range. It 

 has been pointed out by Darwin that the struggle for existence 

 is more severe on large land-areas than on smaller ones, owing to 

 the more complex conditions of life from the larger number of 

 existing species which are able to come into competition. Now 

 the land-areas in the south are very much smaller than in the 

 north, so that it is reasonable to suppose that many genera may 

 have been able to survive in the south with little or no modi- 

 fication, which have been exterminated by the more severe 

 struggle for existence in the north. In this case we should 

 expect to find fossil remains of such geneia, or at all events of 

 nearly related forms, in the north ; and in a great number 

 of cases such fossils have been found. In the pi'esent genus I 

 look on Oockerell's Geotiphia found fossil in Colorado as absolutely 

 congeneric Avith existing South-American species ; and the plant 

 genus Araucaria and many others, which are now southern, had 

 in early geological times a wide range in the Northern Hemi- 

 sphere. It may, of course, be argued that such genera originally 

 had their home in the south and at one time extended their 

 range northward, but in that case it may be conceded that 

 they may have reached the different portions of the Southern 

 Hemisphere by way of the north and not from a southern 

 continent. I must own to an objection to calling up continents 

 from the extreme ocean depths " nisi dignus vindice nodus." 



