TELEOSTOMI 



211 



The spiral valve is present. The double air-bladder aids in 

 breathing. 



The gar-pike (Fig. 172) has a cylindric body covered by 

 rhomboid, bony scales, which are coated with enamel. The 

 snout is long and bony and armed with sharp teeth. This fish 

 is voracious. There are three species found in the fresh water of 

 North and Central America, including Cuba. They are from 

 5 to 10 feet in length. 



Gar-pike {Lcpidos'teus oa'tieus). (After Tenney.) 



The mud-fish or bow-fin is abundant in the shallow waters of 

 the Mississippi Valley. It has a somewhat bony skeleton and a 

 soft flesh, which is not generally used as food. 



Both the gar-pike and the bow-fin come to the surface to emit 

 gases and to take in a fresh supply of air. They can live some 

 time out of water, when they use the air-liladder as a sort of 

 lung. 



Fig. 173.— Cycloid scale. 



Fig. 174. — Ctenoid scale. 



The three foregoing orders are often spoken of as Ganoids. 

 Though now insignificant, they were abundant in the Paleozoic 

 and Mesozoic Epochs. 



Order IV. Teleos'tei. — The skeleton is well ossified. The tail 

 is usually homocercal. There is no spiral valve save in one 

 genus. The scales are cycloid or ctenoid (Figs. 173, 174), or, 

 in rare instances, the body is naked. The operculum is always 



