REPTILES l8l 



together with the length of the head, body and tail in millimeters and 

 that of the tail alone. The color markings are also important, but it 

 must be remembered that many lizards are extremelv' variable in color, 

 as well as exhibiting metachrosis in a high degree. Young animals 

 also often differ totally from the adult in coloration. The character 

 of the scales or plates and the differences between those on the back and 

 the belly are sometimes important, as well as the number of transverse 

 and longitudinal rows. Those immediately in front of the anus are 

 often of characteristic form and number. The plates on the head are 

 usually characteristic and a description of them often enters into a 

 detailed description (Fig. 99), the supraocular scales over the eye, and 

 the upper and lower labials, which bound the lips, being especially 

 important. The character of the tongue is also usually to be noticed; 

 in some families it is thick and little protractile, in others it is similar 

 to the tongue of snakes and may be projected from the mouth as an 

 important tactile organ. In most lizards a row, sometimes double, 

 of conspicuous pores is present on the inner surface of the thigh; they are 

 the femoral pores (Fig. 103). The teeth are usually conical and are 

 never set in alveoli, but become ankylosed usually to the bone of the 

 jaw, either by their base to the edge of the jaw bone, when they are 

 spoken of as acrodont teeth, or by their side just inside the edge of the 

 bone, when they are called pleurodont teeth. 



Key to the Families of American Lacertilia 



ai Legs present. 



bi Skin soft, with minute granular scales i. Gekkonidu'. 



b2 Skin usually scaly. 



Ci Tongue thick and not protractile 2. Iguanidce. 



C2 Tongue protractile. 



di Conspicuous lateral fold present 3. Anguidoe. 



do No such lateral fold. 



Ci Body large and thick; no femoral pores 5. Helodennalidce. 



e2 Body very small and slender; femoral pores 

 present or not. 

 fi Femoral pores present. 



gi No movable eyelids; pupils vertical 6. Xantusiida:. 



go Eyelids movable; pupils round 7. Teiidoe. 



fo Femoral pores absent 8. Scincidcv. 



a2 Legs wanting; body vermiform. 



bi A conspicuous lateral fold; eye and ear opening present .. . 3. Aiigidda'. 

 hi No lateral fold present. 



Ci Scales non-imbricate, in rings; no eye or ear opening. . q. Amphisbcenidos. 

 C2 Scales imbricate, not in rings; no ear opening; eye 



partially concealed 4. .tI nnicllidce. 



