596 PROCEEDINGS OF THE NATIONAL MUSEUM vol.87 



Malaysia. But these forms have not been sufficiently studied and 

 their opalinids are unknown, except for one Australian species which 

 carries Protoopalina, and except also for some few of the species from 

 the highlands of western South America which carry the modern genus 

 Zelleriella, indicating late infection through contact with lepto- 

 dactylids. Full knowledge of their parasites might solve some of the 

 puzzles that we now leave without discussion. 

 Bujo will be treated later. 



THE HYLIDAE (Fig. 152) 



The Hjdidae apparently evolved in tropical America in the heavy 

 forest area for which they are so well adapted. Their ancestors 

 were probably archaic Bufonidae, since pelobatids are not today 

 present in tropical America and apparently never were. Wliat 

 their opalinids w^ere is not clear from any available evidence. The 

 Australian Hylas today bear Protoopalina of subgenus II. The 

 South American forms carry Cepedea and Zelleriella, the latter, I 

 believe, a late introduction (see discussion of the Leptodactylidae). 

 Their Cepedeas probably were introduced to South America by 

 Bufo during the Cretaceous (cf. discussion of Bujo). No Hylas in 

 South America bear Opalina. Apparently Hylas met Opalinae for 

 the first time in the middle Pliocene period after the Isthmus of Pana- 

 ma had been formed and they had crossed into North America. 

 Meeting there Bufos and Ranas, immigrant from Asia, with their 

 Asiatic broad Opalinas, they adopted these and changed them into 

 Opalinae angustae. Spreading over North America these Hylas in 

 turn gave of their narrow Opalinae to certain Ranas and Bufos, to 

 a pelobatid and to a gastrophrynid. - The Isthmus of Panama was 

 completed, apparently in the middle Pliocene (Vaughan, 1919), so 

 that the colonization of North America by hylids and their subse 

 quent wandering across Alaska, Siberia, and on to western Europe 

 was accomplished within the late Pliocene and the Pleistocene periods, 

 an extensive spread in what is geologically a rather brief time. Only 

 a single species, Hyla arborea, with its half dozen or so subspecies, 

 entered Euro-Asia bearing Opalina obtrigona, an American narrow 

 Opalina. Hyla arborea is very closely related to northern North 

 American Hylas. It is not closely similar to any species in Australia. 



Hyla is a vigorous, dominant form to which such an extensive 

 and comparatively rapid spread might be possible. Its behavior 

 is in marked contrast to that of the decadent Ascaphus and the 

 semidecadent Scaphiopus, both of which were in North America 

 earlier than Hyla and merely managed to persist by hiding, one of 

 them (Ascaphus) not having spread at all since the Cretaceous 

 period, and the other (Scaphiopus) spreading east of the mountains 

 only through Western United States and northern Mexico, except 



