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. 
f Ihering, H. von, “ Verbreitung der Ampullarien,” p. 106. 
f Ihering, II. von, “ Archhelenis and Archinotis,” p. 57. 
§ Ortmann, A. E., “Distribution of Decapods,” pp. 292—296. 
|1 Eigenmann, C., “Freshwater Fishes of Patagonia,” pp. 227—229. 
