264 FISHES 



the other hand, are entirely confined to fresh water, namely, 

 the Dipnoi, the Crossopterygians, Polypterus and Calamoichthys, 

 and the Holostei, Lepidosteus and Amia. The Chondrostei or 

 sturgeons also live in rivers, with the single exception of Aci- 

 penser, some species of which descend to the coasts to feed. 



Among the fishes of the familiar scaled and bony type 

 included in the order Teleostei the majority of the families in 

 the five most primitive Sub-Orders, possessing open air-bladders, 

 are inhabitants of fresh water. All the families of the carps 

 and their allies (Ostariophysi) are confined to fresh water 

 except three genera of the Siluridae or cat-fishes which are 

 found along the coasts and in estuaries. Of the Malacoptery- 

 gii, to which salmon and herring belong, the majority of the 

 families, but not all, are entirely confined to fresh water, namely 

 the Mormyridre of Africa, with ten genera, the Hyodontidae, 

 containing only a single genus found in North America, the 

 Notopteridae, with two genera in Africa and southern Asia, the 

 Osteoglossidae, with four genera in the tropics, the Pantodonti- 

 dae, including only the little Pantodon buclilioltzi of West 

 Africa, the Phylactokemidaj, also consisting of one species 

 living in the Nile and Congo, and the Cromeriidae, with a 

 single genus of fishes occurring in the white Nile. The Salmo- 

 nidae range from fresh water to depths of 2000 fathoms in the 

 ocean, and some of the species, like the salmon, migrate from 

 sea to fresh water and back again ; we cannot say why the 

 marine species have not developed spines like the majority of 

 marine Teleosts, but some of them have lost the air-bladder 

 altogether. Of the Clupeidae (herring family) few species are 

 confined to fresh water, but several like the shads of Europe 

 and North America ascend rivers for the purpose of spawning. 

 The Symbranchii live in fresh water, while the Apodes or true 

 eels, like the Salmonidae, range from rivers to the deep sea. 

 Among the Haplomi there are several families characteristic of 

 the fresh-water fauna, such as the Esocidae or pikes, the Cypri- 

 nodonts or toothed carps, of which a few species live along the 

 sea-coasts, the Haplochitonidae of the southern hemisphere, 

 and the Percopsidae ; some of the Galaxiidae go down to the 

 sea to spawn. The Catosteomi or stickleback group as a 

 whole are marine, but several species of sticklebacks are 

 common in fresh waters. The Percesoces {e.g. flying fishes) 



