aceonueidjE. 439 



AcANTHUKUS. — Jaws with a single series of lobate incisors, 

 which are sometimes movable. An erectile spine hidden in a 

 groove on each side of the tail. Ventral fins with one spine 

 and generally five rays. Scales ctenoid, sometimes with minute 

 spines. Branchiostegals five. 



The fishes of this genus, which sometimes are termed 

 " Surgeons," are readily recognised by the sharp lancet-shaped 

 spine with which each side of the tail is armed. When at 

 rest the spine is hidden in a sheath ; but it can be erected 

 and used by the fish as a very dangerous weapon, by striking 

 with the tail towards the right and left. " Surgeons " occur 

 in all tropical seas, with the exception of the eastern part of 

 the Pacific, where they disappear with the corals. They do 



Fig. 193. — Acauthurus leucosternura, Indian Ocean. 



not attain to any size, the largest species scarcely exceeding 

 a length of eighteen inches. Many are agreeably or showily 

 coloured, the ornamental colours being distributed in very 

 extraordinary patterns. The larger species are eatable, and 

 some even esteemed as food. It is stated that the fry of 

 some species periodically approaches, in immense numbers, 

 the coasts of some of the South Sea Islands (Caroline Archi- 

 pelago), and serves as an important article of food to the 

 natives. Nearly fifty species are known. 



At an early period of their growth these fishes present so 

 different an aspect that they were considered a distinct genus, 

 Acronurus. The form of the body is more circular and ex- 



