Bony Fishes. 27 



covered with a lamina of an enamel-like substance. 

 They have likewise unsymmetrical tails and a ventri- 

 cular arterial cone. The gills are free, and are placed 

 on bony gill-arches, under cover of opercula or gillr- 

 flaps, not in pouches nor on plates. Some, like the 

 sturgeons, have a persistent notochord ; others, like 

 the Californian bony pike, have fully ossified verte- 

 bral bodies. The other forms included in this order 

 are the Polypterus of the Nile and the reed fish of 

 Calabar, as well as several rare and curious American 

 species. Many of the fossil forms were of large size 

 and of extraordinary shapes ; their remains abound 

 in some of the old red sandstone formations. All 

 living forms have a swimming-bladder, which in the 

 sturgeon yields the isinglass 1 of commerce. 



17. Order 4, Teleostei. This is by far the largest 

 group of fishes, and includes all those which, like our 

 common fishes, possess a bony skeleton with bicon- 

 cave vertebral bodies. The tail consists of two even 

 lobes supported on a sharply upturned and conti- 

 nuously ossified end of the vertebral column (fig. 6). 

 The body has usually a uniform coating of smooth or 

 ribbed or spinose scales, which rarely have an 

 enamelled surface. The gills consist of free, usually 

 comblike, filaments on bony branchial arches (fig. 10), 

 arranged under the flaplike gill-cover or operculum. 

 There is no arterial cone, the mouth of the ventricle 

 having but one row of valves. 



This order of fishes is divided into the following 

 six sub-orders : 



1 Isinglass is a corruption of the German Hausenblase, from 

 Hauscn, a sturgeon, and Blase, a bladder i.e. sturgeon's bladder. 



