Migrations of North American Birds. 269 



It is a fact not without its significance that the depressed low- 

 land area of eastern America is characterized by the existence 

 of certain genera of fishes and reptiles not found in its Appa- 

 lachian "island. '^ Thus we have Amia, Lepidosteus, Microjiterus 

 [Grystes], and various other forms of fishes throughout the 

 Mississippi valley as far north as the Great Lakes, while in the 

 Atlantic slope they do not pass the James or Lower Potomac 

 except as stragglers. The soft- shelled turtles and the great 

 mass of the Einydidce belong to the same low region also, as 

 well as most of the American perennibranchiate Amphibia, 

 Menopoma (more rarely Menohranchus) alone penetrating into 

 the Appalachian region, while Siredon belongs exclusively to the 

 high central plateau, being found from the Missouri plains to 

 the Cascade Mountains of Oregon and south to the city of 

 Mexico. 



The Unionidce and MelaniadcB seem likewise to belong more 

 especially to the depressed portion of eastern North America. 



I may also mention in this same connexion that, as might be 

 expected, the entire eastern province is characterized by its 

 abundance of Chelonians and Amphibians, the middle and 

 western by their Saurians. Among fishes, the Etheostomoids, 

 Esoces, Siluridce, the freshwater Ganoids {Amia, Lepidosteus, 

 &c.), the fresh-water Percoids, &c. are peculiar to the eastern 

 province, while the great abundance of unusual forms of the 

 Cyprinida is equally distinctive of the middle and western. As 

 regards the fishes, however, the boundaries of the provinces are 

 considerably changed, the eastern including all the waters 

 emptying into the Missouri River and Gulf of Mexico, the 

 middle embracing the region of the Great Basin and the drainage 

 of the Colorado River, and the western the waters discharging 

 into the Pacific. 



The following table presents the species of birds most charac- 

 teristic of each province, the selection having been mainly con- 

 fined to what may be considered as representative species, or 

 those which would formerly have been considered as identical. 

 The isolated species of each province have not been included : — 



