278 A HISTORY OF FISHES 



must have been connected with each other and with continental 

 Europe comparatively recently, "when our eastern, and prob- 

 ably our southern, streams were tributaries of continental 

 rivers and received from them the fishes which they contained ; 

 only nine or ten of these had reached Ireland before it became 

 a separate island, and the distribution of the rest in Britain at 

 varying rates, according to circumstances has not yet proceeded 

 long enough to spread them all over the island." The accom- 

 panying map (Fig. 102) will give some idea of the manner in 

 which the fresh-water fishes reached our islands, and the main 

 routes along which they must have travelled. 



In addition to the families common to the temperate regions 

 of the Old and New Worlds (Esocidae, Umbridae, Cyprinidae, 

 Percidae, etc.), the Nearctic region possesses a number of families 

 occurring nowhere else. These include the archaic Gar Pikes 

 (Lepidosteidae) and Bow-fins {Amiidae), the Moon-eyes (Hiodon- 

 tidae), Blind Cyprinodonts (Amblyopsidae), Trout Perches {Per- 

 copsidae), and Sun-fishes {Centrarchidae) . The order Ostariophysi is 

 represented in this region by a large number of genera and 

 species of Cyprinidae, all of a similar type to those found in the 

 Palaearctic region; the family of Suckers [Catostomidae) , which, 

 with the exception of two species found in China, is confined 

 to North America; and the family of Cat-fishes (Amiuridae) 

 variously known as Amiurids, Horned Pouts, Stone Cats, 

 Channel Cats, Mad Toms, etc., of which only a single species 

 is found outside North America. The Suckers and Cat-fishes 

 have been established in this region for a considerable time, as 

 fossil remains of genera and species not very unlike the existing 

 ones occur in Eocene strata. The Cyprinids, on the other 

 hand, appear to have arrived in the New World much later. 

 It has been stated that during some part of the earlier Cretaceous 

 period India became connected with Eastern Asia, thus allowing 

 the Carps and their allies to spread northward, and there is 

 good reason to believe that during the same time a bridge 

 across the Bering Straits connected Asia with North America, 

 probably serving as a passage for the Suckers and the ancestors of 

 the Amiurids. During the subsequent Eocene period this bridge 

 became broken, but the two continents were once again united 

 during the Oligocene, and it must have been at this time that 

 America received its Cyprinids from Asia, and Asia its two 

 Suckers and one Amiurid from North America. 



