12 BULLETIN 199, UNITED STATES NATIONAL MUSEUM 



Class REPTILIA Laurenti 



Reptilia Laurenti, Specimen medicum exhibens synopsin reptilium, 1768, p. 19. 



Subclasses. — Three subclasses are represented by living members. 

 All occur in Mexico. 



KEY TO MEXICAN' SUBCLASSES, ORDERS, AND SUBORDERS OF REPTILIA 



1. Provided with a shell encasing body above and below, consisting of plastron and 



carapace; turtles. .subclass Anapsida order Testudines (p. 12)_ 5 



Not provided with a shell 2 



2. Anal slit longitudinal; skull diapsid subclass Archosauria. 



order Loricata (p. 209) 



Anal slit transverse; skull modified diapsid; lower (quadratojugal-quadrate) 



arch interrupted.. subclass Lepidosauria order Squamata (p. 37) 



3. Two limbs only, the forelegs; body ringed with grooves. 



suborder Amphisbaenia (p. 37) 

 Four hmbs or none; body not ringed with grooves 4 



4. Limbs present or, if not, movable eyelids present; lizards. 



suborder Sauria (p. 39) 

 Limbs absent; movable eyelids absent; snakes suborder Serpentes 



5. No epidermal scutes on shell 6 



Epidermal scutes present 7 



6. Limbs without external evidence of digits, oar-shaped, clawless. 



suborder Atheca (p. 13) 

 Limbs with distinct digits, 3 with claws suborder Trionychoidea (p. 18) 



7. Limbs oar-shaped, with 1 to 3 claws suborder Carettoidea (p. 14) 



Limbs not oar-shaped, at least foreleg with 4 or 5 claws. 



suborder Cryptodira (p. 18) 



Subclass Anapsida Williston 



Anapsida Williston, Journ. Geol., vol. 25, 1917, p. 419. 

 Orders. — A single living order exists, the Testudines. 



Order TESTUDINES Batsch 



Testudines Batsch, Versuch Anleit. Kenntn. Gesch. Thier. Mineral., vol. 1, 



1788, p. 437. 

 Chelonia Macartney, in Ross, Transl. Cuvier's Legons d'anatomie compar^e . . . , 



vol. 1, 1802, tab. 3. 

 Testudinata Oppel, Die Ordnungen, Familien und Gattungen der Reptilien . . . , 



1811, p. 3. 



Suborders. — Five living suborders of Testudines are recognized; 

 four occur in Mexico, and the fifth (Pleurodira) is restricted to south- 

 ern portions of both hemispheres. 



» Characters in all keys apply to Mexican forms but not necessarily to those in other parts of the world. 



