ORDERS OF AMPHIBIANS 65 



OEDEKS OF AMPHIBIANS 



Note. — If the specimen is not described at the siugle letter, say A, 

 go on to where the letter is doubled, as AA. 

 A. Skull roofed with bone — at least behind the eye. Teeth often 



wrinkled. Fossil. Stegocephala. 



AA. Skull not so roofed. 



B. Legs absent. C^cilians. 



BB. Legs present two or four. 



C. Tail i)resent. Salamander- forms. 



CC. Tail absent. Frog-forms. 



D. Tongue present. 



E. Gristles of breast-bones overlapping. 



Suborder Toads. 

 EE. Gristle of breast-bone not overlapping. 



Suborder Frogs. 

 DD. Tongue absent. 



Suborder Tongueless Frogs. 



The salamander-forms are divided into families by various 

 modes of classifications, based on anatomical differences ; but the 

 following simple artificial key will, by outside features purely, 

 lead to the families (as now divided) : 



TAILED FORMS 

 A. Outside gills gone in the adult. 



B. Eyelids present, no gill-opening (the real salamander-forms). 

 C. Tail round — no fin. Salamanders. 



CO. Tail flat — with a fin above. Neivts. 



BB. Eyelids absent. 



D. Toes two or three behind and three in front. 



Congo Snake. 

 DD. Toes five behind, four in front. 



G ia n t Sa la m a n de r. 

 AA. Outside gills jrresent in adult. 



E. Limbs four. (Proteus), Mud-puppies. 



EE. Limbs two. Sire?is. 



The frog-forms have their suborders scientifically divided 

 into many families, genera, and species. The discussion is too 

 great for our space and too technical for our plan. 



