PHYLUM CHORDATA 



207 



Sub-order e. Plectognathi. 



Teleostei having no pneumatic duct. The exoskeleton, when 

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

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



pclj 



Fie;. 831. Ostracion (Coffer-fish), br. ap. branchial aperture; d.f. dorsal fin; pct.f. pectoral 

 fin ; v. f. ventral fin. (After Day.) 



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. 831). 



Sub-order /. Lophobranchii. 



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

 like, but have their filaments arranged in tufts (Fig. 832, 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. 832), Pipe-fishes and their allies. 



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

 distinguished from Physostomi by the closed air-bladder. 



Systematic Position of the Example. 



Salmo fario is one of several species of the genus Salmo, belong- 

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

 order Teleostei. 



