858 



SCIENCE. 



[N. S. Vol. XII. No. 310. 



the Ancient Relations between New Zea- 

 land South America.' Transactions of the 

 Kew Zealand Institute, Vol. XXIV., 1891, 

 p. 431-445. 



4. ' Die Palaeo-Geographie Suedameri- 

 kas.' Ausland, Stuttgart, 1893, Nos. 1-4. 



5. ' Revision der von Spix in Brasilien 

 gesammelten Najaden.' Arehiv. fur Natur- 

 geschichte, 1890, p. 117-170, Taf. IX. 



6. ' Najaden von S. Paulo und die geo- 

 graphische Verbreitung der Suesswasser- 

 faunen von Suedamerika. ' Arehiv. fur Nat- 

 urgeschichte, 1893, pp. 45-140, Taf. III.- 

 IV. 



7. ' Das neotropische Florengebiet und 

 seine Geschichte.' Engler^s Botanisehe Jahr- 

 hiieher, Vol. XVII., 1893, pp. 1-54. 



8. ' Die Ameisen von Rio Grande do Sul.' 

 Berliner entomologische Zeitschrift, Band 39, 

 1894, pp. 321-446. 



9. ' Os molluscos dos terrenos terciarios 

 da Patagonia.' Eevista do Museu Paulista, 

 Vol. II., 1898, pp. 217-382, PI. III.-IX., 

 with Conclusions in English, pp. 372-380. 



The study of the fresh water fauna, and 

 especially of the Unionidse of South America, 

 gave me as a practical result the separation 

 of two sub-regions 'Archiplata ' and 'Archa- 

 mazonia.' The first contains Chili, Ar- 

 gentina, Uraguay and Southern Brazil, the 

 second Central and Northern Brazil (Archi- 

 brazil) and Guyana, Venezuela, etc. (Archi- 

 guyana). Archiplata contains numerous 

 genera of Mollusca, Crustacea, etc., that are 

 common to Chili and the La Plata district, 

 such as Lhiio, Chilina,Parastacus,Aeglea, etc., 

 including many species and even their para- 

 sites (Temnocephala), which ai*e identical on 

 both sides of the Andes. This contrasts 

 sharply with the Archamazonian fauna, as 

 tropical genera extend to Rio Plata and Rio 

 Negro which are completely wanting in 

 Chili and Peru. In Ecuador, however, the 

 Cordillere form no such zoogeographical 

 division, due certainly to differences in the 



geological history of both parts of the 

 Andes. For example the Decapod Crus- 

 tacea in Chili and in the whole of Archi- 

 plata are the Parastacidse and Aegleidse, 

 but the Potamoninse are in Archamazonia. 

 Dr. Ortmann has opposed to my explana- 

 tions the hypothesis that biological difier- 

 ences may be the true reason, exterminating 

 the Potamoninse thatinvaded Archiplata, but 

 favoring the Parastacidse. The observations 

 made by the writer on the biology of these 

 Crustacea emphatically annul the objection. 

 In Northern Argentine, Rio Grande do Sul 

 and St. Catherina, both coexist in the same 

 waters and while the Potamonidse prefer 

 rivers and brooks, living among aquatic 

 plants, the Parastaeus selects muddy terri- 

 tory where it can burrow. 



That the explanation is a geographical one 

 is proved also by the fact that the species 

 of Unionidaj, Mutelidse, Ampullariidse, etc., 

 which occur in the La Plata and in the Rio 

 Paraguay, are almost all Amazonic spe- 

 cies. Moreover the faunal relations of the 

 Parang River are totally different from 

 those of the Paraguay River. In confirma- 

 tion of these zoogeographical facts the geo- 

 logical ones indicate to us in the Entrerian- 

 formation Unio of the Nisea group, Chilina, 

 Strophocheilus, etc., that is to say, the pure 

 Archiplata fauna. These facts point out 

 that the invasion of the Archamazonian 

 element into Archiplata is quite a recent 

 one. The intrusion of the Archamazonian 

 element is Pliocene or post-Tertiary, and the 

 Andes formed a barrier insurmountable to 

 fresh-water crabs and mussels as well as to 

 fishes, chelonians and alligators. 



It is evident that the two faunal ele- 

 ments of South America correspond to geo- 

 graphical districts which were separated by 

 the ocean during the greater part of the 

 Tertiary. The intermixture of the two ele- 

 ments, and especially the intrusion of Boliv- 

 ian ants, land snails, etc., in Eastern Brazil 

 is by no means finished, but is a fact which 



