288 GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. 



elevated mountains. The loach has been found in the Himalayas 

 at an altitude of eleven thousand feet, and in the South American 

 Andes, Lake Titicaca, at an altitude of thirteen thousand feet, 

 has yielded several species. Indeed, in the latter region, some of 

 the Alpine cyprinodonts, as Trichomycterus, penetrate to heights 

 of fifteen thousand feet, and upwards. 



Fresh- Water Fishes. It will be evident from the present rela- 

 tion existing between land and water which in its general features 

 unquestionably dates from a very remote geological period and 

 the resulting barriers opposed to a free migration, that fresh-water 

 fishes will be much more limited in their range than the fishes of 

 an oceanic type, whose distribution is in main part governed by 

 conditions of food-supply and temperature, and to a certain extent 

 by the nature of oceanic currents. This comparative areal restric- 

 tion among fresh-water forms is exemplified not only in the case of 

 species and genera, but also in that of families, none of which, if 

 we except the cat-fishes (Siluridae), can be considered to be in any 

 way cosmopolitan. Manifestly, the oceanic basins must prove to 

 the animals of this class an obstruction much in the manner that 

 it does to the higher animals, the reptiles and mammals, for ex- 

 ample. Yet, certain peculiar occurrences would seem to indicate 

 that the natural barrier thus formed is not in all cases as effectual 

 in preventing the distribution of fishes as it is with the majority of 

 the animals just mentioned. Thus, several identical species, as the 

 salmon (Salmo salar), perch (Perca fluviatilis), burbot (Lota vul- 

 garis), pike (Esox lucius), and a stickleback (Gasterosteus pungitius), 

 inhabit alike the waters of Europe and Eastern North America; 

 the perch of the Ganges and other East Indian rivers (Lates cal- 

 carifer) is found in the waters of Queensland, Australia; and one 

 of the forms of south temperate so-called " trout" (Galaxias atten- 

 uatus) inhabits Tasmania, New Zealand, the Falkland Islands, and 

 the southern extremity of the continent of South America. In 

 addition to such divided species, representing, naturally, divided 

 genera as well, there are also several generic types whose lim- 

 ited number of representatives (while distinct specifically) be- 

 long to opposite quarters of the globe. The genus Umbra, limited 

 to two species, is represented in the Atlantic States of the American 

 Union by the " dog " or "mud fish " (U. limi), and in the Danubian 

 system of waters by the * ' Hundsfisch " (U. Krameri) ; the shovel- 



