322 



BULLETIN 120, UNITED STATES NATIONAL MUSEUM, 



there was connection between Euro- Asia and extreme western United 

 States, but the migration which brought to America the ancestors of 

 Scaphiopus and its Protoopalinas quite likely occurred later, for. 



neither host nor parasite are present in South America. The evolu- 

 tion of Scaphiopus and of its Protoopalinas in North America was 

 probably Tertiary or later (figs, 237, 238). 



