190 VERTEBRATA. 



In the male of Callorhynchus antarcticus there is a peculiar 

 prehensile organ on the upper part of the snout. The subarctic 

 and Mediterranean Chimcera monstrosa is known to the northern 

 fishermen as " King of the herrings." 



There is only one family : 



Chimaride. *Edaphodon. 



Chimaera. *Passalodon. 



Callorhynchus. *Elasmodus. 



Order VIII. GANOIDEL 



Skeleton variously ossified ; gills free ; gill-aperture with gill- 

 cover. Body covered with plates or scales which are composed 

 of two layers, the upper of enamel, the lower of bone, or occa- 

 sionally naked. 



The notochord is frequently persistent in the extinct forms. 

 The vertebras, when developed, are ainphicoelous, except in Lepi- 

 dosteus, which approaches the Reptilian type in being opistho- 

 eoelous. The bulbus arteriosus, provided with numerous valves, 

 is rhythmically contractile, as in the Chondropterygii. The fins 

 are often studded on the fore edge with a single or double row of 

 spiny scales (fulcra). The tail-fin is mostly unsymmetrical. 



The living species are only about 35 ; the extinct forms are nu- 

 merous (about 600 species), occurring principally in the Old Red 

 Sandstone ; among the recent ones we have the bony pike (Lepi- 

 dosteus osseus), sturgeon (Acipenser sturio), beluga (Acipenser huso), 

 and sterlet (Acipenser rutkenus). They generally ascend rivers 

 for the purpose of spawning. 



Isinglass is prepared from the air-bladder of sturgeons ; caviare 

 or botargo is the roe (sometimes weighing 800 Ibs.) of the beluga. 



The Ganoids have been divided into two groups or orders 

 (J. Miiller) Chondroganoidea or Chondrostei [a cartilaginous 

 skeleton] and Osteoganoidea or Holostei [an osseous skeleton]. 

 Another mode of division is into Placoganoidea [more or less 

 protected by large osseous plates] and Lepicloganoidea [covered 

 with scales]. The Crossopterygidas of Huxley comprise Poly- 

 pteridse, Holoptychiidse, &c. Schmarda's arrangement is here 

 followed, except that Ceratodida3 are referred to Dipnoi. 



(Chondroganoidca.) Pterichthyida. Pycnodontidae. 



Cephalaspidce. *Coccosteus. *Platysornus. 



*Cephalaspis. *Pterichthys. *Pleurolepis. 



*Pteraspis. *Pycnodus. 



