THE OPALINID CILIATE INFUSORIAXS. 369 



and narrow Opalinas. The absence of Gastrophrynids from Aus- 

 tralia is an indication, but not of course conclusive, that they 

 were not present in the Patagonian fauna at the time Patagonia was 

 united to Australia and that the route to Australia, taken by the 

 Brazilian Hylids, was not open to them. It is likely the Gastro- 

 phrynids in South America were confined to the Guiana highlands 

 until after routes of migration from South America to Australia 

 had been permanently closed. The Gastrophrynidae seem a fairly 

 vigorous family so that the negative evidence from their absence from 

 Australia deserves emphasis. Their presence in Papua and in an ad- 

 jacent island just to the west of it is a puzzle, emphasizing again the 

 need of review of all the evidence as to the paleogeographic relations 

 of Papua. The genera in the Eastern Hemisphere are much more 

 numerous than those in America, indicating that probably the 

 family arose in the east. 



The Opalinid parasites of the Gastrophrynidae do not throw much, 

 if any, light upon the problem of their distribution. It is in two 

 Central America species of Gastrophryne that we find two Proto- 

 opalinae (P. ovoidea and P. xyster) which seem transitional forms 

 between the Protoopalinae and ZellerieTlae. It is, however, evident, 

 on the basis of broader data already reviewed, that Zelleriella arose 

 in southern South America, before its union with the northern por- 

 tion of the continent. Protoofdlina xyster^ which by its flattening 

 approaches Zelleriella^ is found, not in any species which could have 

 been an early inhabitant of Argentina-Patagonia, but in a species 

 from a family not represented in the early southern fauna, a Gas- 

 trophryne^ probably descended from an immigrant from Africa to 

 Guiana. As the toads, and to a less extent the frogs, adopted Zel- 

 leriella from the Leptodactylids, when these families met after the 

 disappearance of the trans- South American sea, so also the American 

 Gastrophrynids, under similar conditions, secondarily acquired Zel- 

 leriella. Protoopalina xyster may be a ref)resentative of an early 

 group of southern South American species, originally parasitic in 

 Leptodactylids, which were transitional between Protoopalina and 

 Zelleriella. It is curious, but not at all inexplicable, that our only 

 at present known examples of these transitional forms have survived, 

 not in an original Leptodactylid host, but in a secondarily adopted 

 Gastrophrynid host. 



The Gastrophrynidae apparently arose in early Cretaceous times 

 (fig. 234) in South Atlantis, or more probably in its Madagascar- 

 India extension. Persisting in India during the early Tertiaiy (fig. 

 236), they entered Asia in the late Tertiary (fig. 237). Their pres- 

 ence in Papuasia is unexplained. 



