CLASSIFICATION 377 



forms, and have been considered in some detail in the previous 

 chapter. The third includes the vast majority of living Bony 

 Fishes, and is further sub-divided into some thirty-one orders of 

 varying size and importance. The Bow-fin {Amia) of North 

 America is the sole existing survivor of the first of these orders, 

 the Protospondyli ; the second, or Ginglymodi, includes the 

 fresh-water Gar Pikes (Lepidosteidae) of North America ; and the 

 third, or Halecostomi, contains the Herring-like Pholidophoridae 

 already mentioned {cf. p. 362). The Isospondyli, the first of the 

 orders of modern Bony Fishes, is an important group, including 

 a vast assemblage of genera and species, all of which agree in 

 having the air-bladder connected with the gullet by a pneumatic 

 duct, and the pelvic fins abdominal in position. This is split 

 up into seven sub-orders, of which the more important are the 

 Clupeoidea, including the Ten-pounders (Elopidae), Lady-fishes 

 (Albulidae), Herrings (C/z/p^f^^^), Smooth-heads {Alepocephalidae) , 

 Milk-fishes {Chanidae), etc.; the Stomiatoidea, oceanic fishes dis- 

 tinguished by the presence of luminous organs or photophores; 

 and the Salmonoidea, including the Salmon, Trout, and their 

 allies (Sabnonidae) , Argentines {Argentinidae) , Smelts {Osmeridae), 

 etc. The remaining sub-orders of importance are the Osteo- 

 glossoidea, Notopteroidea, Monnproidea, and Gonorhynchoidea. 



From the generalised Isospondyli have been derived a number 

 of more specialised orders, represented on the tree (Fig. 135) by 

 a group of radiating branches. These include the Haplomi, 

 containing the Pikes {Esox), Mud-fishes {Umbra), and Black-fish 

 {Dallia); the Iniomi, containing the Lizard-fishes {Synodontidae) , 

 Lantern-fishes or Myctophidae, and a number of other oceanic 

 forms; the Giganturoidea, a very small order of specialised oceanic 

 fishes; the Lyomeri or Gulpers, closely related to the Iniomi; the 

 Apodes, containing all the Eels; and the Heteromi, a small group 

 of fishes living at considerable depths in the oceans. The huge 

 order, Ostariophysi, which includes the vast majority of the 

 fresh-water fishes of the world, is closely related to the Isospondyli, 

 diflfering only in the presence of the complicated Weberian 

 mechanism {cf. p. 193). Two sub-orders of the Ostariophysi 

 are recognised: the first, or Cyprinoidea, containing the Carps 

 and allied forms {Cyprinidae) , as well as the Characins {Charac- 

 inidae, etc.), Gymnotidae, Suckers {Catostomidae) , and Loaches 

 {Cobitidae) ; and the second, or Siluroidea, all the families of 

 Cat-fishes. Another fairly important order derived from the 

 Isospondyli is the Synentognathi, a group which includes the Gar- 

 fishes {Belonidae), Half-beaks {Hemirhamphidae) and the true 



