216 ZOOLOGY SECT. 



arch are fused to form a single bone in the floor of the mouth (Fig. 

 890, B). The remaining characters are as in Acanthopteri. 

 Including the Wrasses (Fig. 890) and their allies. 



Sub-order~e. Plectognathi. 



Teleostei having no pneumatic duct. The exoskeleton, when 

 present, takes the form of bony plates or spines. The gill-opening 



brafi 



FIG. 891 Ostracion (Coffer-fish), br. ap. branchial aperture ; d.f. dorsal fin : pet f pectoral 

 fin ; t>, /. ventral fin. (After Day.) 



is very narrow. The mouth is very small, and the premaxilla and 

 maxilla are united. The pelvic fins are absent or represented by 

 spines. 



This is a small sub-order, including the File-fishes, Globe-fishes, 

 Sun-fishes and Coffer-fishes (Fig. 891). 



Sub-order f. Lophobranchii. 



Teleostei having no pneumatic duct. The gills are not comb- 

 like, but have their filaments arranged in tufts (Fig. 892, B). The 

 branchial aperture is very small. The exoskeleton consists of 

 bony plates arranged segmentally. 



This is also a very small sub-order, including only the Sea- 

 horses (Fig. 892), Pipe-fishes and their allies. 



Sub-orders b f are frequently grouped together as Physodisti, 

 distinguished from Physostomi by the closed air-bladder. 



Systematic Position of the Example. 



Salmo fario is one of several species of the genus Salmo, belonging 

 to the family Salmonidce, of the sub-order Physostomi and the 

 order Teleostei. 



The absence of a spiral valve and of a conus arteriosus, the 



