444 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 91 



Ortmann (1902, p. 341) in his discussion of the geographic distribu- 

 tion of fresh-water Crustacea and its bearing upon ancient geography 

 stated that "the presence of the genus Parastacus on both slopes of the 

 Cordilleras (even the identical species is found in one case on both 

 sides, and in this respect Aeglea agrees with Parastacus) points to a 

 time when the Cordilleras had not j^et attained their present eleva- 

 tion. As von Ihering [1907, 1911] has shown, for many groups of 

 animals this chain forms a very sharp barrier, and it does not seem 

 probable that these freshwater Crustaceans are able to cross these 

 high snow and ice covered mountains," Although this may well 

 have occurred, it is not very necessary to presuppose that Aegla 

 reached its continent-wide distribution before the Andes attained 

 their present elevation, for, in spite of the height of this great 

 mountain range and the rigors of the climate investing its summits, 

 there certainly are passes, particularly in the lake region of Chile 

 and Argentina, through which Crustacea such as Parastacus and 

 Aegla might have made their way in times past, if not present. 



There must be a pass of this sort above the headwaters of the Rio 

 Petrohue and Lago Todos Santos, where are to be found "on top 

 of the pass of Perez two small streams, one flowing toward the 

 Pacific, the other toward the Atlantic * * * (Eigenmann, 1928, 

 p. 25). Today one can go by bus, automobile, motor boat, and 

 steamer from Chile to Argentina by way of Petrohue, Lago Todos 

 Santos, Peulla (elevation 190 meters), Casa Pangue, Chile (elevation 

 320 meters) , Lago Frias, Argentina, to Puerto Blest on Lago Nahuel 

 Huapi, Argentina (elevation 756 meters). 



Insofar as they apply to the same geographic area, I am most 

 anxious to have an opportunity of checking Dr. Eigenmann's findings 

 (1928, especially references given in the partial bibliography on p. 2) 

 based on his studies of the fresh-water fish fauna, its distribution, 

 and origin, against that of Aegla. But before that can be done, 

 vastly more Aegla material than has yet been collected would have 

 to be assembled. 



There seems to be a relation of sorts between our rostral types 

 and such of the "environment complexes in which the sum total of 

 the natural conditions are about equal" of Haseman (1912, pi. 15). 

 The forms with the ridge-roofed, Atlantic type of rostrum more or 

 less occupy Haseman's "Uruguay-Rio Grande do Sul" area plus 

 some additional territory to the south and west, while the Andean 

 or Pacific type, along with the intermediates, A. jujuyana and A. 

 franca^ occupies his "West Andean," "Patagonian," and "Alto Parana 

 and its affluents" areas. As the forms with Andean type of rostrum 

 are found in each of the last-named "environmental complexes" of 

 Haseman, they must have something in common, be it geologic his- 

 tory, environment, or something else. 



