CHAPTER XYI 



OUTLINE OF MODERN REPTILES AND SOME HELPFUL KEYS 



To help recall the pecuharities of the various 

 orders of living reptiles the following outline in the 

 form of a key is submitted, presenting apparent as 

 well as structural features : 



Note. — If one peculiarity is noted at a certain letter the oppo- 

 site will occur where the letter is found doubled. 



A. Form tortoiselike ; a distinct shell. Shell either leathery or 

 horny; mouth beaklike — no teeth; back-bone and ribs fast 

 to shell (one exception). Tortoise-forms. 



AA. Form not tortoiselike ; either lizardlike or snakelike ; jaws 

 with evident teeth ; back-bone always movable everywhere. 

 B. Tail with a double crest near the body ; skin covered with 

 plates placed edge to edge ; heart four-chambered ; toes 

 four behind, five before. Crocodilians. 



BB. Tail, toes, skin, etc., not as above ; heart never four-cham- 

 bered. 

 C. Teeth in upper jaw appearing to be in two rows — the 



lower teeth shutting between. Tuatera. 



CC. Teeth in upper jaw not appearing to be in two rows, 

 though teeth may be present on f)alate. 

 D. Lower jaw solid at chin — not jointed or loose. 

 Limbs present or absent, but there is always a 

 shoulder-girdle. Lizards proper. 



DD. Lower jaws held together at chin by a ligament 

 merely. No true limbs with toes. No shoulder- 

 girdle ; eyelids never apparent. Tongue always 

 forked, slim, and sheathed. Serjjents. 



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