EUROPO-ASIATIC EEGION. 245 



which the Cyprinoid type reaches. The PJiodeina are a small 

 family especially characteristic of the East, but with one or 

 two off-shoots in Central Europe. Very significant is the 

 appearance in China of a species of the Catostomina, a group 

 otherwise limited to North America. 



The Cyprinoids, in their dispersal from the south north- 

 wards, are met from the opposite direction by the Salmonoids. 

 These fishes are, without doubt, one of the youngest families 

 of Teleostei, for they did not appear before the Pliocene era ; 

 they flourished at any rate during the glacial period, and, 

 as is testified by the remnants which we find in isolated 

 elevated positions, like the Trout of the Atlas, of the moun- 

 tains of Asia-Minor, and of the Hindu Kush, they spread to 

 the extreme south of this region. At the present day they 

 are most numerously represented in its northern temperate 

 parts ; towards the south they become scarcer, but increase 

 again in numbers and species, wherever a great elevation offers 

 them the snow-fed waters which they affect. In the rivers 

 of the Mediterranean Salmonoids are by no means scarce, 

 but they prefer the upper courses of those rivers, and do 

 not migrate to the sea. 



The Pike, Umbra, several species of Perch and Stickle- 

 back, are also clearly autochthont species of this region. 

 Others belong to marine types, and seem to have been re- 

 tained in fresh water at various epochs : thus the freshwater 

 Cottus (Miller's Thumb) ; Cottus quadricornis, which inhabits 

 lakes of Scandinavia, whilst other individuals of the same 

 species are strictly marine ; the Burbot (Lota vulgaris) ; and 

 the singular Comephorus, a dwarfed and much-changed Gadoid 

 which inhabits the greatest depths of Lake Baikal. 



Eemnants of the Palseichthyic fauna are the Sturgeons 

 and Lampreys. The former inhabit in abundance the great 

 rivers of Eastern Europe and Asia, periodically ascending 

 them from the sea ; their southernmost limits are the Yang- 



