xii AGAMIDAE 515 



Group I. Zonuridae and Anguidae assume a central position, with Iguanidae 

 and Agamidae as two parallel families of highest development. 

 Aniellidae as the most degraded forms. Helodermatidae and 

 Lanthanotidae as rather primitive and solitary survivals. 



Agamidae Iguanidae 



I 



Xenosauridae 



I., 



Zonuridae Anguidae Helodermatidae. 



I 

 Aniellidae. 



Group II. Xantusiidae Tejidae Amphisbaenidae. 



Group III. Scincidae Gerrhosauridae Lacertidae. Here also Anelytro- 



pidae and perhaps also Dibamidae as degraded Scincoids. 

 Group IV. Varanidae, which are in many respects the most highly developed 



of all. 

 Pygopodidae are of 'obscure relationship. 



Fam. 1. Agamidae. Acrodont, Old-World Lizards, with a 

 broad and short tongue. The teeth are usually differentiated 



I AGAMIDAE. 

 FIG. 122. Map showing the distribution of the Agamidae. 



into incisors, canines, and molars. The orbit is closed posteriorly : 

 the temporal fossa is bridged over by an arch which is formed 

 chiefly by the squamosal and the well-developed jugal ; the post- 

 orbital mostly remaining small, and the postfrontal and supra- 

 temporal bones being either absent or not present as separate 

 elements. The limbs are well developed. The eye, provided 

 with complete eyelids, is distinctly small and has a round pupil. 

 The skin is devoid of osteoderms, although large and numerous 

 spines are often present, especially on the head and on the tail. 

 The Agamidae, of which about two hundred species, arranged 



