The Squamipinnes 



407 



Mexico, and is generally common, though rarely entering rock 

 pools. 



Zanclus eoccenus is recorded from the Italian Eocene. 



The Tangs: Acanthuridae. In the next family, Acanthuridcz, 

 the surgeon-fishes or tangs, the scales remain small and shagreen- 

 like, the body is more elongate, the gill-openings still more 

 restricted, and the teeth are flattened and incisor-like. The pubic 

 bone is more elongate, and in all the species some sort of arma- 

 ture is developed on the side of the tail. The spinous dorsal 



FIG. 343. Teuthis cceruleus (Bloch & Schneider), Blue Tang; Medico. 

 Family Teuthididce. 



in all is less developed than the soft dorsal. The species abound 

 in the warm seas, especially about the tide pools, and are used 

 as food. They undergo considerable changes with age, the 

 caudal armature being developed by degrees. Nearly all are 

 dull brown in color, but in some a vivid ornamentation is added. 

 Fossil forms are found from the Eocene and later. Most of 

 these are referable to Teuthis and Acanthurus. 



The principal genus is Teuthis, characterized by the presence 

 on each side of the tail of a sharp, knife-like, movable spine 

 with the point turned forwards and dropping into a sheath. 

 This spine gives these fishes their name of surgeon-fish, doctor- 



