I 



OPALINID CILIATE INFUSOKIANS — METCALF 



THE PELOBATIDAE (Fig. 150) 



595 



These toads are found today in the lands north and east of the 

 Mediterranean Sea, in Asia south and southwest of the Himalayas, in 

 Malaysia and Papua, and in North America. Their origin and spread 

 seems to parallel that of the Discoglossidae. They probably evolved 

 in India or in southeastern Asia in Cretaceous times after Australia 

 had separated from Asia, They seem to have passed to the Mediter- 

 ranean lands by a route that lay either to the north or to the south 

 of the Himalayas; to have passed to Malaysia and Papua during the 



Figure 151.— Geographic distribution of the Bufonidae, other than Bufo. 



time of fluctuations when the Malaysian and Papuan connections were 



repeatedly formed and broken (late Tertiary or Quaternary, fig. 145); 



to have passed during the earUer or later Tertiary by way of Siberia 

 I and Alaska to North America, this northeastward migration including 

 I only the one genus, Scaphiopus, or rather its ancestors. The opalinids 

 I of the Pelobatidae were originally Protoopalinas of subgenera II and 



III and they still are, fexcept for the very compact group of species, 

 I subgenus VI, evolved in Scaphiopus since its migration to North 



America, and except also for certain adventitious, late Tertiary in- 

 : fections in Scaphiopus in North America by two species of Zelleriella 



and two species of narrow Opalinae. These infections were apparently 



since the middle Phocene, i. e., since the Isthmus of Panama was 

 I formed. 



THE ARCHAIC BUFONIDAE (Fig. 151) 



These genera I am discussing apart from the remarkable genus 

 Bujo. Their present distribution indicates an origin in the Southern 

 Hemisphere in pre-Cretaceous times, before Australia separated from 



