PERCIFORMES 



435 



Division B. Plectognathi. Here the maxilla becomes fixed to, and 

 generally fused with, the premaxilla ; the jaws become short and stout, 

 and the upper jaw does not slide forwards, but becomes hinged on the 

 ethmoid so as to bite up and down (Fig. 453). The subocular shelf is 

 lost ; the post-temporal loses its lower branches and fuses with the 

 supratemporal. The pelvic bones become firmly united, narrow, and 

 elongated. The gill-membranes fuse with the isthmus, and the branchial 

 opening becomes restricted. 



Subdivision A. Family Teuthididae. The body is compressed, the 

 tail armed with movable lateral spines fitting in a groove, the dorsal and 

 anal fins with many spines, the small jaws provided with a single row of 





Fig. 444. 

 Platax teim, Forsk. (After Day, Fishes of India.) 



incisiform teeth, the palate toothless, the gill-membranes attached. The 

 post-temporal is still forked. 



Teuthis, L. (Fig. 445) ; Indo-Pacific. Archaeoteuthis, Wettst. ; Eocene, 

 Europe. 



Family Siganidae. The post- temporal is not rigidly fixed, the 

 suborbital shelf is lost, but the myodome is present. The parietal is 

 lost. The pelvic fin has 6-7 spines, and the pelvic is peculiar in having 

 a posterior as well as an anterior spine, and four soft rays (Starks [42 2a]). 



Siganus, Forsk. ; Pacific. 



Family Acanthuridae. The body is compressed, covered with 

 minute ctenoid or spinous scales. One spine and five jointed dermo- 



