DISCUSSION. 417 



Mr. Fletcher — Before considering the case of the Australian 

 Batrachia, the obvious, important, natural barriers which have 

 been mainly instrumental in bringing about the existing distri-. 

 bution and segregation of species, may be pointed out — the Great 

 Dividing Range, Torres Straits, Bass Straits, and the climatic 

 barrier due to the aridity of dessicated Central Australia. The 

 first of these is the oldest; but in places, at any rate, it is not an 

 absolute barrier to some species; and it runs out altogether to 

 the south-west. The others are believed to be not older than 

 Post-Pliocene. The second, Torres Straits, must be left out of 

 account because of the lack of knowledge enabling one to com- 

 pare the Batrachian faunas of North-East Australia and New 

 Guinea. The contiguous faunulae into which the barriers indi- 

 cated have subdivided the Batrachian fauna, are not specially 

 remarkable for the number of geminate species which they offer. 

 They may be described, in general terms, as comprising repre- 

 sentatives of widely spread species which had already attained a 

 very wide distribution before the barriers indicated (the Dividing 

 Range, perhaps, excepted) had become effective, or of slightly 

 modified forms — colour-varieties, geographical races or subspecies, 

 not entitled to receive sj»ecial names; together with a few species 

 (like the Tasmanian and Victorian species of Crinia, for example) 

 which are perhaps entitled to be considered geminate forms : or 

 of such an assemblage, together with local species, and representa- 

 tives of restricted or even monotypic genera. For instance, a 

 Tasmanian collection of frogs might be successfully passed off upon 

 an unsuspecting biologist as a South Victorian collection. The 

 frogs of King Island, in Bass Straits, as far as known, are to be 

 found in both Tasmania and South Victoria; and the freshwater 

 fishes in one or the other, or in both (Johnston). On the other 

 hand, allied forms certainly do occur in the same area, without 

 any discernible physical barrier operating, so far as one can judge 

 — e.g., Hyla ewingii var. calliscelis and H. krefftii; Limnodynastes 

 tasmaniensis and L.Jletcheri Blgr.; Pseiidophryne australis and 

 P. hihronii. In such cases, physiological isolation probably 

 functions as a barrier. As far as the Australian Batrachia 

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