GENERAL CLASSIFICATION 161 



29. Derinopterous Holobranchs. [Skin-fins. H. E. ] 



Salmo. "I Characinus.\ p . w t? i 



Osmerus (amelt). V[Salmonidae. H. E.] Serrasalmo. J '■'"'^*'^*""'°*®- ■"• ^' J 

 Corregonus, j 



30. Siagonote Holobranchs. [Long-jawed. H. E.] 

 Elops. Sphyraena. 

 Megalops (tarpon). Lepisosteus. 



Esox. Polypterus [Ganoid. H.E.]. 



Synodon. Scorabresox. 



(2) An operculum over the gills, hut no membrane. 

 Sternoptyges. [Bent sternum. H. E.] 



.31 



Sternoptyx. 



(3) No operculum over the gills, but a membrane. 

 Cryptobranchs. [Gills hidden. H. E.] 



32 



Mormyrus. 

 Stylophorus. 



(4) No operculum nor membrane over the gills : no inferior 



paired fins. 



Ophichthians. [Snake-fishes. H. E.] 



33 



Unibranch aperture. Murenophis. 



Sphagebranchus. Gymnomuraena. 



Remark. Seeing that the formation of a skeleton begins in the 

 fishes, those called cartilaginous are probably the least perfect fishes. 

 Consequently the most imperfect of all should be Gasterobranchus, 

 which Linnaeus, under the name of myxine, had regarded as a worm. 



Thus, in the order that we are following, the genus Gasterobranchus 

 must be the first of the fishes, because it is the least perfect. 



REPTILES. 



(Class XII. of the Animal Kingdom.) 



Oviparous vertebrate animals with cold blood ; breathing incompletely 

 by a lung, at all events in later life ; and having the skin smooth or 

 else covered either with scales or with a bony shell. 



Observations. 



Progress in the perfection of organisation is seen to be very remark- 

 able in the reptiles when they are compared with fishes ; for it is among 



