XIII 



PHYLUM CHORDATA 



207 



Sub-order c. 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 



bra/3 



pclj 



FIG. 831. Ostracion (Coffer-fish). Ijr. up. branchial aperture ; <i.f. dorsal fin ; pct.f. pectoral 



fin ; r. 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 / 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 Sal-mo, belong- 

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

 order Teleostei. 



