vi] DISTRIBUTION OF SELECTED GROUPS 97 



early Miocene most of the chief families seem to 

 have been already developed. Unfortunately our 

 knowledge of their pedigrees is still very deficient. 

 It is for instance at least doubtful whether the 

 'Firmisternia' (Ranidae + Engystomatidae + Dysco- 

 phidae) form a natural division. Only the more 

 significant cases of distribution can be mentioned. 

 The most archaic but also most specialised are the 

 Aylossa, namely Pipa, the 'Surinam toad/ mainly 

 Brazilian, Xenopus in Africa, and Hymenochirus, 

 intermediate in structure, in the Congo district. 



The Discoglossitlae also are ancient, with a very 

 scattered range, namely the 'fire-bellies/ Bombinaior, 

 from France to Manchuria, the 'midwife toad,' Alytes, 

 IHscoglossiis in West Europe, and Ascaphus in North- 

 West United States. The equally ancient Pelobatidae 

 or 'spade-foots' and allies range from North America, 

 Europe and India into Papuasia. 



Bufonidae, typical ' toads, 1 are cosmopolitan, ex- 

 cepting Madagascar, New Guinea, Tasmania and New 

 Zealand. The genus Bufo has the same wide range, 

 but is also absent from Australia. The centre of the 

 Hylidae or 'tree-frogs' is South America, whence 

 they have spread, since the Miocene, to the Antilles 

 and Central America, and in ever decreasing numbers 

 into North America, and only two or three closely 

 allied species occur in Eurasia, from Japan to the 

 Himalayas and to western Europe, excluding Britain. 



G. 



