eigenmann: fresh water fishes. 307 



the lake formed huge inlets or deep bays, now represented only by the 

 nearly dry river-beds flowing into the lake at Aygache, Gorilla and Guajui. 

 The sluggish Desaguadero must have been a strait of considerable width, 

 with large islands ; and this long lake, connecting Lake Titicaca with 

 Lake Aullagas, must have equalled in extent the upper lake, the upper 

 lake, at that time, extending across the Isthmus of Yunguyo, leaving the 

 Peninsula of Gopacabana, as a large island, connected with the lower lake 

 by a broad pass between the hills to the west of Gopacabana, and those 

 to the west of Yunguyo. The plains, now laid bare at the northern 

 and western shores of Lake Titicaca, give us an excellent idea of the 

 appearance the whole basin of the lake would present if entirely dry. 

 The number of lakes and basins, great and small, which formerly covered 

 the elevated plateau of the Andes, must have been very great ; but we 

 now find only here and there a small sheet of water. The former lakes 

 are only represented by the more or less extensive pampas, forming basins 

 at great altitudes, showing plainly that the whole of this district is receiv- 

 ing a much smaller waterfall than in former times, but probably not within 

 historic times, if we take into consideration the position of some of the 

 most ancient ruins of Bolivia (at Tiahuanaco), which are only about 75 

 feet above the present level of the lake."^ 



The area to which Lake Titicaca belongs probably remained separate 

 from Ecuador until long after the latter was colonized from Archiguiana, 

 and the Brazilian fauna did not gain access to the Titicacan region until 

 after the elevation of the lake had become too great for most of the Bra- 

 zilian types of fishes. 



I give below a list of the species of the Northern and Titicacan prov- 

 inces with the localities from which they are recorded. The Northern 

 province is characterized by several genera, some of them undoubted 

 derivatives of the neighboring lowlands marked " / " and by others on the 

 western slope derived from the sea marked " Me." Rhamdia and Pygidiiim 

 have a wide distribution. The Titicacan province is characterized by the 

 extravagant genus Oresfias, which has developed from a Fiindulus-\\\iQ 

 species received when the lake was still an arm of the sea.^ 



^ See also page 372. 



^The crustacean fauna is even more evidently of marine origin. The genus Orc/ustia, with 

 its seven Titicacan species, is still preeminently a marine genus. 



