726 MR. E. E. TIRXER ON 



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

 owing to ditiereuces of stvueture. espeoially in the tarsal ungues, 

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

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

 species are bifid. The neui-ation is t^o vaiiable, 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 Colohosila Sichel and Callosila 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 initil moi-e species are known in both sexes any 

 subdivision would be i-Jish and unnecessary. 



The geographical distribution of the genus is interesting, being 

 almost entirely Southern, inclndiug Australia (wheie the species 

 are most numerous). South America as far north as the Ama/.on, 

 ^[adagascar and South Africa spreading up the East African 

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

 I'egard similar cases of distribution as a proof of southern origin, 

 and explain them by former noi'thern 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 and other similar cases of 

 disti'ibution 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 sevei-e 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 

 noi'th, so that it is reasonable to suppose that many genera mav 

 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 noith. In this case we should 

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

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

 of eases such fossils have been foiuid. In the present genus I 

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

 congeneric with existing South- American species ; and the plant 

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

 in eai'ly geological times a wide range in the Koi-thern Hemi- 

 sphei'e. It may, of course, be argued that such genei-a 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 i-eached the dift'erent portions of the Southern 

 Hemisphere by way of the iiorth 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." 



