THE OPALINID CILIATE INFUSORIANS. 385 



of species in recent times, for there is no species or genus common to the two 

 continents. The South American and African elements of these two families 

 must have been derived from some intermediate land mass or must have gone 

 from one continent to the other over a land bridge. 



As to the Antartic relations of Patagonia we may quote again from 

 Eigenmann (1920). Writing of the fresh-water fishes of the Pacific 

 slope of South America he says : 



One of the questions of interest and importance was where did the fishes 

 of the Pacific slope of South America come from? To answer this question 

 we dipped into many of the rivers emptying into the Pacific from Panama 

 to Puerto Montt. The Irwin expedition has demonstrated that the present con- 

 dition is not the primitive condition and the present fish fauna is but a relict 

 of the past. Both in Peru and in Central and northern Chile there are great 

 valleys and water courses that must, in the past, have carried groat streams. 

 At the present time some of these contain water w'hen the snow melts or 

 when rain falls in the mountains, some are permanently dry. At Piura I 

 asked an urchin where the river was ; he answered, " It has not come down 

 yet but w'e expect it next Saturday." Under such conditions very few fishes 

 have been able to survive. Going south from the extremely wet country 

 of southern Colombia, one species of fish after another drops out until, in 

 northern Chile, nothing is left. Fishes appear again south of Copiapo in 

 Chile, and the first fish is a little thing about 2 inches long, a left over or 

 stray from the Amazon region. Farther south, about Santiago, there is a 

 new lot of fishes that " knew not Brazil," and still farther south, about Con- 

 cepcion, another group starts in, becoming dominant about Puerto Montt. 

 (Farther I could not go.) This new fauna in southern Chile is more closely 

 related to the fishes of New Zealand than to those of Brazil. They <late back 

 to a time when Patagonia was part of a continent separate from northern 

 South America. 



The indications involved in the distribution of the Opalinids and 

 their hosts have been stated with but little discussion of geological 

 and other data bearing upon the problems presented. This does not 

 seem the place to enter upon an extended comparative discussion 

 of zoogeography. I am accepting here, for convenience of reference 

 a set of charts mainly from Arldt (1907) but much modified. It is 

 for the zoologist to develop the zoological data, and for the geologist 

 and paleographer to treat critically the geological data. Few new 

 conceptions of geologic phenomena have been presented in this 

 paper. All the land connections and their dating, to which we have 

 referred, have been widely discussed by others; the conditions our 

 maps show in the South American continent and its connections are 

 rather different from prevalent conceptions. The data from Opali- 

 nidae and their hosts give new evidence which must be correlated 

 with the evidence from other sources. 



In our review of Anuran and Opalinid geography and its impli- 

 cations, we have found general agreement with the conclusions, 

 from much wider data, expressed in Arldt's charts. This statement 

 may well stand as the summary of all our discussion of this subject. 



