92 FISH GALLERY. 



by their vegetation shelter to these defenceless creatures. They are 

 bad swimQiers, and are frequently and resistlessly c?rried by currents 

 into the open ocean or to distant coasts. All enter brackish water, 

 some fresh water. Tlie males of most of the species carry the eggs 

 either in a sac at the base of the tail, or attached to the abdomen. 

 The best known are the Pipe-fishes {Syngnathus) and the Sea-horses 

 {Hippocampus) . 



Order VI. PLECTOGNATHI. (Cases 25-27.) 

 Teleosteous fishes with rough scales, or with ossifications of the 

 cutis in the form of scutes or spines ; skin sometimes entirely naked. 

 Skeleton incompletely ossified, with the vertebrae in small number. 

 Gills pectinate ; a narrow gill-opening in front of the pectoral fins. 

 Mouth narrow ; the bones of the upper jaw generally firmly united. 

 A soft dorsal fin, belonging to the caudal portion of the vertebral 

 column, opposite to the anal ; sometimes elements of a spinous 

 dorsal besides. Ventral fin none, or reduced to spines. Air- 

 bladder without pneumatic duct. 



This Older consists of two families, Sclerodermi and Gym- 

 nodontes. 



The Sclerodermi com'^vxse the genera Triacanthus, Balistes, Mona- 

 cujtt/ms, and Ostracion. The File-fishes [Balistes, fig. 80) inhabit 



I'ig. 80. 



File-fish (Balistes vidua). (From the Indian Ocean.) 

 the tropical and sub-tropical seas ; both jaws are armed with eight 

 strong incisor-like and obliquely truncated teeth, by which these 

 fishes are enabled to break off pieces of corals on which they feed, 

 or to chisel a hole into the hard shells of Mollusca, in order to 



