THE OPALINID CILIATE INFUSORIANS. 361 



The Pelobatidae (fig. 224, p. 288). 



The Pelobatidae are known from southern Europe, southern and 

 eastern Asia and the East Indies, and from the United States of 

 America and Mexico. Megalophrys^ from Java, carries Protoopalina 

 mo?itanu. Pelobates, from Europe, bears Protoopalina pelobatidis 

 and "P. intestinalisy Pelodytes from Europe has not been ade- 

 quately studied, onW a single individual having been opened, and this 

 with negative result. The only American genus, Scaphiopus, bears 

 Protoopalina, Zelleriella, a very doubtful Cepedea {flava) and nar- 

 row Opalinae. The Opalinid parasites of this family throw little 

 light upon the problem of its geographical distribution. The Amer- 

 ican Scaphiopus was probably evolved in America from immigrant 

 ancestors. Its Zelleriella parasites must have been adopted in Pliocene 

 times or later in America, after southern South America, the home 

 of the Zelleriellas, had united with tropical America. Its narrow 

 Opalinae also are American. Its Cepedea {floridensis) was probably 

 adopted from immigrant hosts coming from Siberia, or from their 

 descendants. Its Protoopalinas are characteristic forms, probably 

 of American origin in this American genus of hosts. They resemble 

 the species of the intestinaUs group more than any others and prob- 

 ably were evolved from them, and this is added indication that the 

 ancestors of Scaphiopus came to America from the Orient by way of 

 Alaska, for Euro- Asia is the chief locality for the intestinalis group 

 of Protoopalinas. ^ 



This is an old family. Their absence from Australia. Africa and 

 South America indicate a post-Triassic origin (fig. 232). Their 

 occurrence in Papua is a puzzle. Bufonids, Pelobatids. and the an- 

 cestors of the Hylids and Leptodactylids probably all arose from 

 related stocks and the place of origin was probably eastern Equa- 

 toria. The early Bufonids spread chiefly westward to Africa and 

 South America, but are in Australia also. The Hylids and Lepto- 

 dactylids arose in South America probably from the earliest Bu- 

 fonids. 



The ancestral branch which gave rise to the Pelobatidae moved 

 northward from eastern Equatoria into the continent of Asia, prob- 

 ably just about the time Australasia separated from Asia-Malaysia, 

 that is, during the last of the Jurassic (figs. 233, A, 234). They may 

 have spread to Europe in Cretaceous times (fig. 234), or more likely 

 during the later Tertiary (fig. 237), at which time Malaysia, which 

 had been submerged during the Cretaceous and the early Tertiary, re- 

 emerged and received Pelobatids from southeastern Asia. The pres- 

 ence of Pelobatids in Papua and not in Australia is an indication, in 

 line with evidence from Rana and the Gastrophrynids which we shall 



83103—2.3 24 



