152 ON SYSTEMATIC ZOOLOGY. 



and, possibly, Linnaeus, when he placed the cartilaginous 

 fishes among the reptiles, may have had some indistinct 

 perception of their union. It has, however, been re- 

 marked, that this arrangement was made on the suppo- 

 sition of their being furnished both with lungs and gills; 

 an idea which seemed confirmed by the observations of 

 Dr. Garden, of Carolina, who, at the request of Lin- 

 naeus, examined the organs of the genus Diodon, and 

 found, as he conceived, both external bronchiae, or gills, 

 and internal lungs. This idea, however, has been shown 

 by later physiologists to have been not strictly correct ; 

 the supposed lungs being, in reality, only a peculiar mo- 

 dification of gills.* The genera of the Amphibia are 

 thus characterised : 



I. REPTILES. With feet. 



Testudo. Tortoise. Body four-footed, covered with a shell. 

 Draco. Dragon. Body four-footed, tailed, and winged. 

 Lacerta. Lizard. Body generally four-footed, tailed, and 



naked. 



Rana. Frog. Body four-footed, naked, tailless. 

 Siren. Siren* Body two-footed, tailed, naked. 



II. SERPENTES. Feet none. 



Crotalus. Rattlesnake. Plates on the belly and tail j with a 



rattle. 



Boa. Boa. As above ; but without a rattle. 

 Coluber. Viper. Plates on the belly ; scales on the tail. 

 Anguis. Snake. Scales on the belly and tail. 

 Amphisbaena. Jllindworm. Rings on the belly and tail. 

 Caecilia. Snake-worm. Body with naked lateral wrinkles. 



III. NANTES. Provided with fins instead of feet ; breathe by 

 spiracles. 



Petromyzon. Lamprey. Spiracles seven, placed on the sides. 

 Raja. Ray, or Thornback. Spiracles five, placed beneath. 

 Squalus. Shark. Spiracles many, five on each side. 

 Chimera. Sea Monster. Spiracle solitary, quadrifid. 

 Lophius. Fishing Frog. Spiracle solitary ; ventral fins two, 



like feet. 

 Acipenser. Sturgeon. Spiracle solitary ; ventral fins two ; 



mouth without teeth. 



* Gen. Zool. vol. iv. p. 13. 



