442 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 91 



even lesser extent may support more than one species (i. e., Buenos 

 Aires and adjacent region, two species: A. platensis and A. uru- 

 guayana; and Montevideo and vicinity, three species: A. 'platensis^ 

 A. Uruguay arm ^ and A. prado). (Fig. 40.) 



The presence of two or more species in one locality, as in Buenos 

 Aires and its environs and perhaps also Montevideo, may have 

 resulted from the tremendous floods to which at least the lower 

 reaches of the several rivers that converge to form the Rio de la 

 Plata are subject. Such an agency would serve to bring together in 

 the same region species that otherwise might exist at some distance 

 from one another. 



Generally speaking, most of the species seem rather circumscribed 

 in their distribution (but it must be remembered that the number of 

 records we have for any one species is still very small). If this 

 is so, the Aeglas may be very responsive to their immediate environ- 

 ment, very plastic forms, or else the species are very "young." 



The climatic extremes encountered by Aegla in its geographic 

 range are considerable (Koppen, 1930, fig. 41). These, too, may 

 have a marked effect not only on the distribution of the species but 

 on their actual development or evolution. Two species that may 

 be a living demonstration of the effects of climatic conditions, which, 

 after all, are but a part of the environment of a species, are A. 

 jujuycma and A. hwmaMiaca. So far as we know now the two are 

 scarcely more than 70 miles apart at their point of nearest approach, 

 yet, on the basis of precipitation figures alone, they are a vastly 

 greater distance apart. At Jujuy, Province of Jujuy, Argentina, 

 the type locality for A. jujuy ana^ as much as 29.26 inches of rain 

 falls during the year, with some rain in each of the twelve months; 

 at Humahuaca, in the same province, the type locality for A. 

 hwTiahuMca^ on the other hand, the total yearly rainfall, 6.11 inches, 

 is less than that of the wettest month of the year at Jujuy (January, 

 with 6.65 inches), while five months (May to September) are wholly 

 without appreciable precipitation (Reed, undated MS. ; see footnote, 

 p. 500). 



If it is true that the least differentiated, least spiny or ornamented 

 species stands nearest the ancestral Aegla, then perhaps our A. 

 jujuyana is least removed from it in an evolutionary sense. This 

 would place the center of distribution somewhere in the northwestern 

 part of Argentina (Province of Jujuy), which is at variance with 

 Ortmann's belief (1902, p. 389) that Aegla was originally indigenous 

 to Chile and subsequently extended into northern Argentina and 

 southern Brazil, or perhaps in the reverse direction. 



A. jujuyana lacks or has not yet developed the palmar crest that 

 is so characteristic of almost every other species of Aegla; its rostrum 



