268 THE OSTEOLOGY OF THE REPTILES 



mous "Gila Monsters" of Arizona. They are thickset, slow lizards 

 with a club-like tail, reaching a length of about two feet, the only 

 known poisonous members of the suborder. 



Eocene. Glyptosaurus Marsh, Thinosaurus Marsh, North Amer- 

 ica. Placosaurus Gervais, France. 



Oligocene. Helodermatoides Douglass, North America. 



Family Lacertidae. Quadrupedal, terrestrial lizards. Upper sur- 

 face of skull with numerous dermal bones. Temporal opening roofed 

 over by the postfrontal extending back between parietal and squa- 

 mosal, the arches complete. A parietal foramen. Teeth pleurodont. 



The family of Lacertidae comprises about one hundred species 

 restricted in distribution to Europe, Asia, and Africa. None is large 

 and some are common throughout England; one, Lacerta vivipara, is 

 the only reptile known to occur in Ireland. 



Miocene. Lacerta, France. 



Family Tejidae. Arboreal, terrestrial, or subaquatic lizards at- 

 taining a length of three feet. No postorbito-squamosal arch.^ A 

 parietal foramen. No dermal ossicles. Zygosphenes sometimes 

 present. 



A family of American lizards including about one hundred species, 

 some, like the Cnemidophorus , common throughout the United 

 States. The teeth of Dracaena are large oval, crushing organs. 



Uppermost Cretaceous. ? Chamops Marsh, North America. Oligo- 

 cene, Tejus. 



Family SciNCiDAE. Temporal arch complete. Temporal openings 

 roofed over by dermal bones. Body also covered by dermal ossicles 

 beneath the corneous scales. Quadrupedal, bipedal, or limbless; 

 terrestrial, subaquatic, or burrowing. Pleurodont. 



The large family of skinks comprises about four hundred li\dng 

 species, cosmopolitan in its distribution. Some attain a length of 

 about two feet. Trachysaurus of AustraUa is peculiar in its stumpy 

 tail and very large scales of the body. Cyclodus has spherical crush- 

 ing teeth. 



Lower Cretaceous (Neocomian). Ardeosaurus Meyer. 



Eocene. Cadurcosaurus Filhol, France. 



' [A postorbital arch is present. — G. K. N.] 



