THE SUBCLASS PARAPSIDA 265 



A. Suborder Lacertilia (Sauria)i 



Subvolant, arboreal, terrestrial, burrowing, subaquatic, or marine 

 reptiles from a few inches to about forty feet in length ; quadrupedal, 

 bipedal, or limbless; herbivorous, insectivorous, or carnivorous. 

 Brain-case in front of prootics more or less membranous. Lacrimals 

 small or vestigial. Posterior arcade sometimes absent. Mandibles 

 usually united by suture. Vertebrae procoelous, except in the Geck- 

 onidae and Uroplatidae ; not more than two sacral vertebrae. Clav- 

 icles and interclavicle rarely absent. No entepicondylar, but usually 

 an ectepicondylar foramen in humerus. 



This group is often given an ordinal rank, equivalent to the Ophidia 

 or even to the Pythonomorpha, but the ultimate distinctions be- 

 tween them are almost trivial, as will be seen, and in many legless 

 burrowing lizards the skull structure mimics that of the snakes. 

 More than eighteen hundred species are known, distributed widely 

 throughout the world, usually classed in about twenty families and 

 numerous genera. 



Because of their predominantly terrestrial habits, but few remains 

 of lizards are found in the rocks, aside from the more aquatic or 

 marine types. Only about fifty genera of extinct forms have been 

 described and less than one hundred species, and the greater majority 

 of those are for the most part fragmentary and incomplete, so much 

 so that their systematic positions are very often uncertain and pro- 

 visional. Doubtless they have had a long and abundant geological 

 history from very remote times, but of the true land lizards almost 

 nothing is known throughout the Mesozoic. But few positive char- 

 acters are distinctive of the group, though many negative ones are. 

 The mandibles are usually suturally united in the middle, but a few 

 forms have them ligamentously attached. The presence of legs is not 

 distinctive, though at least a vestige of the pectoral girdle remains. 

 The more or less open brain-case in front is perhaps the most 

 diagnostic, only partially enclosed by the more or less vestigial post- 

 optics ("alisphenoids," "postorbitals"). However, in the Amphis- 

 baenia even this character is doubtful, and in the mosasaurs a dis- 

 tinct descending plate from the parietals resembles that of the snakes, 



^ [For a very comprehensive morphological and taxonomic revision of the Lacertilia, 

 see C. L. Camp, " Classiiication of the Lizards," Bulletin, Amer. Mus. Nat. Hist., 1923, 

 XLViii. — Ed.] 



