440 FISHES. 



ceedingly compressed. N"o scales are developed, but the 

 skin forms numerous oblique parallel folds. The gill-cover 

 and the breast are shining silvery. 



Nasbus. — Tail with two (rarely one or three) bony keeled 

 plates on each side (in the adult). Head sometimes with a bony 

 horn or crest-like prominence directed forwards. Ventral fins 

 composed of one spine and three rays. From four to six spines 

 in the dorsal ; two anal spines. Scales minute, rough, forming a 

 sort of fine shagreen. Air-bladder forked behind. Intestinal 

 tract with many circumvolutions. 



Twelve species are known from the tropical Indo-Pacific, 

 but none of them extend eastwards beyond the Sandwich 

 Islands. In their mode of life these fishes resemble the 

 Acanthuri. Likewise, the young have a very different appear- 

 ance, and are unarmed, and were described as a distinct 



Fig. 194. — Naseus unicornis. 



genus, Keris. One of the most common species is N. unicor- 

 nis, which, when adult '(22 inches long), has a horn about 

 2 inches long, whilst it is merely a projection in front of the 

 eye in individuals of 7 inches in length. 



Prionurus is an allied genus with a series of several keeled 

 bony laminae on each side of the tail. 



Second Family— Caeangid^. 



Body more or less compressed, oblong or elevated, covered with 

 small scales or naked ; eye lateral. Teeth, if ^present, conical. 

 No tony stay for the prceoperculum. The spinaus dorsal is less 

 developed than the soft or than the anal, either continuous with, 

 or separated from, the soft portion ; sometimes rudimentary. 



