THE SPECIES OF AEGLA — SCHMTTT 443 



is somewhat intermediate between the flatter, troughed (Pacific or 

 Andean) type^ present in species found on the east and west slopes 

 of the Andes and the more spinelike, ridge-roofed (Atlantic type) 

 rostra of the species of the great region more or less immediately 

 tributary to the River Plate. 



Of special interest in this connection is the fact that we meet also 

 with the so-called Pacific or Andean type of rostrum in the Serra 

 do Mar bordering the Atlantic coast of Brazil, in Santa Catharina 

 {A. odehrechtii) and in Sao Paulo {A. odebrechtii paulensis). This 

 discontinuous distribution of the forms with the Pacific or Andean 

 type of rostrum may be apparent only. 



From the center in Argentina at or in Jujuy it may be that the 

 forms or variants with the Pacific type of rostrum spread out west- 

 ward to the Andes and beyond to Chile and eastward to the Serra do 

 Mar of Brazil, while down the vast Argentine Rio Parana drainage 

 area and across to at least the lower reaches of the Rio Uruguay to 

 Rio Grande do Sul, and to Parana, migrated those that developed 

 what I have called the Atlantic type of rostrum. Not fitting in with 

 this speculative scheme of things is A. franca, from Franca, Sao Paulo, 

 Brazil, also a species with what might be called the more intermediate 

 type of rostrum found in A. jujuyana. It could be a northeastern 

 offshoot of the original or ancestral jujuyana stock, or else a reversion 

 to the ancestral condition of a Brazilian form with the Pacific type of 

 rostrum. 



The marine origin of Aegla appears indisputable, and therefore it 

 is of more than passing interest that the general region in which 

 A. jujuyana is centered has geologically had a long-continued marine 

 history, with marine deposits antedating the Devonian, up through 

 the Carboniferous (Berry, 1922). Since Cretaceous time that part 

 of South America seems to have been wholly continental and its 

 waters no longer marine. Undoubtedly the elevation of the land 

 above the sea was gradual, or at least long enough drawn out to 

 allow the ancient forebears of the Aeglas of today to adapt them- 

 selves to progressively less saline and increasingly fresher waters. 



Although there are a few very fragmentary crustacean remains 

 said to be decapod in tlie Permian, the first unquestionable fossil 

 decapods, already well differentiated into groups or tribes, families, 

 genera, and species, are Tnassic (Zittel, 1913, p. 760; Glaessner, 

 1929, pp. 404, 462). Galathea first appears in the Upper Cretaceous. 

 Pseudogalathea from the Lower Carboniferous of Scotland, however, 

 has been assigned to the "schizopoda" by paleontologists (Zittel, 

 1913, p. 757). 



" A more detailed description of these types of rostra will be found on p. 448 of the notes 

 on "characters used in diagnostic key and specific descriptions," and in the key itself, 

 pp. 451 and 454. 



