418 DISCUSSION. 



are concerned, a reasonable conclusion seems to be that the 

 existing physical barriers are not sufficiently old, geologically 

 speaking, in most cases nothing like so old as Miocene; or not 

 absolutely impassable and effective; or, when climatic, liable to 

 intermittent or partial break-downs; and that, for these or 

 other reasons, Jordan's Law is not strikingly applicable. 



Mr. Froggatt exhibited specimens representing six species, 

 referable to three genera, of the Family Cicadidce; which, he con- 

 sidered, might fairly be called three pairs of geminate species. 

 (1) Thopha saccataYahv., is confined to the south and east coasts 

 of Australia, from South Australia to Brisbane; it is the largest 

 species common about Sydney; the country about Gosford and 

 Newcastle is one of its favourite localities. T. sessiliba Dist., 

 was described from Townsville, Q.; it ranges from the Northern 

 Territory to Townsville; recorded also from Tennant's Creek, 

 N.T., and Goonowindi at the head of the Barwon River, on tlie 

 Queensland border. The break between the areas over which 

 these two species are distributed is well marked; though Goono- 

 windi is about in line with the northern limit of T. saccata, 

 there is a good barrier offered b}' a mountain range. (2) Cysto- 

 soma saundersi West wood, was formerly common at Ash Island, 

 Hunter River; it is not found south of Sydney, Gosford being its 

 southern limit; recorded also from Armidale, Glen Innes, and 

 the Bellenger River; but not known from any locality north of 

 the Richmond River. G. schmeltzi was described by Distant, 

 from Gayndah, Q.; it occurs also in the neighbourhood of Towns- 

 ville, Q. The southern species was common in Citrus orchards 

 in 1860; it is found on sweetbriar at Armidale, and at Glen 

 Innes upon the willows; this points to the fact that its native 

 scrub food has been destroyed. The barrier between the two 

 species is due to the character of the country, with a scarcity of 

 scrub on the coast to the south of Townsville. (3) Tetligarcta 

 tomentosa White, from Launcestou, Tasmania, living in fern-tree 

 gullies, according to Mr. Simson; it has been erroneously recorded 

 from Victoria; but is not found on the mainland, though Distant 

 incorrectly gives the habitat as Australia in his Catalogue(1906). 



