DISTRIBUTION AND LOCATION 271 



neighbourhood of coral reefs, are the Chaetodontidae and Poma- 

 centridae. Both of these families are perciform fishes of 

 rather small size, short in proportion to their depth and in 

 the case of the Chaetodonts flattened from side to side ; they are 

 extremely active and alert, and are remarkable for their vivid 

 colours and conspicuous markings (see Frontispiece) ; bordered 

 patches or ocelli and sharply defined bands of the strongest 

 colours occur in the greatest variety in the different species, 

 and the contrasts between these markings and the ground 

 colour are often intense. In fact the riotous development of 

 colour which is exhibited by tropical birds and butterflies is 

 equalled if not surpassed by these fishes. In Chaetodontidae 

 and several allied families the scales extend on to the surface 

 of the dorsal and ventral fins, for which reason the group is 

 often called Squamipinnes meaning scale-finned, and these fins 

 are often prolonged backwards into tapering filaments. Species 

 of Chaetodon occur in the West Indies and on other Atlantic 

 coasts, and on the Pacific coast of Mexico, but they are most 

 numerous in the East Indies. Some species of the family are 

 excellent food-fishes, for example two species in the West 

 Indies. The allied family Acanthuridae is distinguished as the 

 name implies by a knife-like movable spine on each side of the 

 tail, from which they get the English name surgeon-fishes. 

 Tenthis is a typical genus with species in the West Indies, on 

 the west coast of Central America, and from India to Hawaii. 

 In Scorpididae the most remarkable fish is Psettus sebae which 

 lives in the East Indies; it is the deepest bodied of all fishes in 

 proportion to its length, the vertical diameter at the broadest 

 part being twice the length. A similar extension of the flat 

 body in the vertical direction is characteristic of the species of 

 Platax, known as the Sea-bats ; Platax orbicularis ranges from 

 India to Japan ; this genus is included by some authorities in 

 the Chaetodontidae 



Related to the Squamipinnes through the Acanthuricke, 

 from which they are derived by progressive modification, are 

 the curious fishes of the Sub-Order Plectognathi, {i.e. with united 

 jaw-bones), which are highly characteristic of tropical coasts. 

 They are usually divided into three divisions: Sclerodermi {i.e. 

 hard-skins) with a spinous dorsal fin, scales, and separate teeth ; 

 Ostracionts, with no anterior dorsal, the scales replaced by bony 



