FAUNISTIC AFFINITIES 405 



Professor Tullberg's* reference to a pre-Tertiary land 

 bridge between South America and south-west Africa is not 

 very definite. From his remarks it is not clear that he is in 

 favour of the existence of an independent connection far to 

 the south of the one I discussed in the last chapter. 



These are among the more important results derived from 

 the study of the fossil fauna of Argentina as to the affinities 

 presented by this part of South America to the more distant 

 parts of the world. We have still to consider the faunistic 

 kinship between Argentina and the neighbouring states of 

 South America. Dr. von Ihering f pointed out long ago that, 

 whereas America as a whole is the richest part of the world 

 in the variety of genera and species of fresh-water mussels, 

 Chile and Peru belong to the poorest districts, since, at any 

 rate west of the Andes, only the genus Unio occurs. Similarly 

 Ampullaria and many other typically American fresh-water 

 genera are absent from Chile. On the other hand, the Unios of 

 Chile are most of them nearly related to those of the La Plata 

 region. Dr. von Ihering J concludes from these very peculiar 

 zoographical features that, while the whole of southern South 

 America ( Archiplata) formed a united land-mass in Secondary 

 times, the elevation of the Andes afterwards prevented a 

 faunistic interchange between the two districts. The fresh- 

 water Crustacea tell us a very similar story. The fresh-water 

 crayfish Parastacus is met with in eight species in South 

 America. None of them occur north of southern Brazil, 

 although several ,of the Chilean species are closely related to 

 Brazilian ones. The fresh-water crab Aeglea laevis, no doubt 

 an exceedingly ancient form and the only representative of the 

 family Aegleidae, lives in identically the same species on both 

 sides of the Andes. The absence of almost all the leading 

 genera of Brazilian fishes from Chile and Patagonia, || empha- 

 sises the noteworthy distinctness in the fresh-water fauna of 

 the two regions. On the other hand, Patagonia and Chile 

 present traces of a relationship, as I intend to show later on, 



* Tullberg, Tycho, " System der Nagetiere," p. 495. 



t Ihering, H. von, *' Verbreitung der Ampullarien," p. 106. 



t Ihering, H. von, " Archhelenis and Archinotis," p. 57. 



Ortmann, A. E., "Distribution of Decapods," pp. 292296. 



|| Eigenmann, C., "Freshwater Fishes of Patagonia," pp. 227229. 



