TELEOSTEL 571 



which they swallow whole. They are the largest fresh-water fishes, 

 for A. sturio may attain a length of 1 8 ft. and a weight of 600 lb., 

 while the A. huso of Southern Russia may measure 25 ft. and weigh 

 nearly 3000 lb. ! Most of the species are found both in the sea and in 

 rivers or lakes. The roes or ovaries form caviare ; the gelatinous 

 internal layer of the swim-bladder is used as isinglass. 



The genus Scaphirhynchus is represented in Asia and the United 

 States ; Polyodon or Spatularia spatula is the paddle-fish or spoon-bill 

 of the Mississippi. 



Order 3. HOLOSTEI J with bony skeleton 



Living examples \Lepidosteus and Amia. 



Extinct examples : Lepidotus, Pycnodus, Aspidorhynchus. 



The N. American bony pike Lepidosteus is covered 

 with rows of "ganoid" scales; the whole skeleton is well 

 ossified, and the vertebral bodies are opisthoccelous ; the 

 swim-bladder is like a lung in structure, and to some 

 degree in function. The bow-fin, Amia calva, frequenting 

 still waters in the United States, has a similar lung-like 

 swim-bladder. Its scales are similar to those of a Teleost. 



Order 4. TELEOSTEI. The " Bony Fishes " 



This order includes most of the fishes now alive. 

 Though comparatively modern fishes, they are older than 

 was formerly supposed, as several Jurassic genera (Thrissops^ 

 Leptolepis, etc.), which used to be classed as "Ganoids," 1 

 must be considered as actual Clupeoids, or herring-like 

 Teleostei. It is, however, not until the Upper Cretaceous 

 and Tertiary epochs that they assume among fishes that 

 overwhelming preponderance in numbers which they possess 

 at the present day. The physostomous type of Teleostean 

 is the most ancient, and probably stands in a continuous 

 genetic line with the Holostei. 



The skeleton is well ossified, with numerous investing 

 bones on the skull, others in the operculum, and on the 

 shoulder-girdle. There is always a supra-occipital in the 



1 The term "Ganoids," which we abandon, is often used to include 

 Crossopterygii, Chondrostei, and Holostei. Though they agree in 

 having a conus arteriosus with many valves, as opposed to the 

 Teleostean bulbus, an optic chiasma, as opposed, to the decussate 

 condition in Teleosts, and an intestinal spiral valve which is absent in 

 Teleosts, they do not seem to form a natural division. 



