THE OPALINID CILIATE INFUSORIAXS. . 367 



bridge in the late Cretaceous or early Tertiary. They spread 

 throughout northern South America in the middle Tertiary and 

 either then or in the later Pliocene passed on to Central America 

 and North America. In the later Pliocene they passed to the West 

 Indies and the Bahamas from Central America. Probably during 

 the same period one species passed by way of Alaska to Siberia, 

 China, Europe, and northern Africa, evolving as it went into three 

 (four?) closely related species, one of which has diverged into four 

 Cfive?) subspecies. 



We have noted that the Hylidae, whose original Opalinids were 

 Protoopalinae, have been in general inhospitable to the binucleated 

 Zelleriellas, but have accepted some Cepedeas and are chiefly infected 

 with Opalinas. Although originally bearing parasites of a binu- 

 clated genus they later were more ready to accept multinucleated 

 guests than binucleated Zelleriellas, and this too in spite of the fact 

 that they have been in contact with Zelleriellas for a considerable 

 period, that is since the early or middle Pliocene. 



The Leptodactylidae (fig. 228, p. 292) . 



The Leptodactylidae are very abundant in South America; are 

 numerous in Central America ; have barely passed the barrier of the 

 northern Mexican desert, being represented in Texas by two species ; 

 have entered the West Indies, but are only sparcely represented 

 there; they are well represented in Australia and Tasmania; one 

 genus, Liopelma, with two species, is in New Zeland, being the only 

 Amphibian there; and one species has recently been reported from 

 Papua. Heleophryne, of southern Africa, originally classed as a 

 Ranid, has recently been shown to have an arciferous sternum and 

 has been assigned to the Leptodactylidae. Dr. L. Stejneger suggests 

 in a letter to the author that, as this is the youthful condition of the 

 sternum in the Ranidae, Heleophryne may be a Ranid with arrested 

 development. The occurrence of a true Leptodactylid in Africa 

 seems so utterly anomalous that I am leaving this form out of account 

 in the discussion of distribution. I venture the prediction that 

 Heleophryne will not be accepted finally as a Leptodactylid. As 

 an illustration of the conclusive character of evidence from parasites 

 we may note that were Zelleriella, the Opalinid of the Leptodacty- 

 lidae, known from Heleophryne we should have to accept the latter 

 as a Leptodactylid and set ourselves to solve the puzzle of its occur- 

 rence in Africa. But there is little likelihood that this South Ameri- 

 can Opalinid will be found in this African Anuran. The connection 

 between southern Africa and Patagonia was apparently broken too 

 early to serve as a bridge for Leptodactylids. 



The Leptodactylidae seem an Antartic family, with much the same 

 history as their cousins the Hylidae. They arose apparently in 



