226 REPORT OF NATIONAL MUSEUM, 1898. 



2. A^ertebrre without zygospheii. 



* Posterior cranial borders not spinous, 

 t Superciliary and labial scales segmental. 



Tail sbort, spinous ; a gular fold lloplocercus Fitzinger. 



tt Superciliary scales imbricate; labials segmental. 



A gular fold ; occipital plate small Croiapliytus Holbrook. 



A gular fold, witb enlarged scales; occipital plate large, 



Uta Baird and Girard. 

 A gular fold without enlarged scales ; occipital plate large . Lijsoptychus Cope. 



No gular fold ; occipital large Sceloporus Wiegmaun. 



tt Both superciliary and superior labial scales imbricate. (A gular fold.) 



Tympanum exposed; occipital plate small; digits fringed Uma Baird. 



Tympanum exposed; occipital large; digits not fringed, 



Callisaurus Blainville. 

 Tympanum concealed ; occijiital large ; digits not fringed, 



Solbrookia Girard. 

 ** Posterior borders of cranium with bony spines. Two hepatoventral mesenteries. 

 Labial and superciliary scales not imbricate ; occipital scale small ; a gular 

 fold ; body short, depressed ; ribs elongate. 



Tympanic drum exposed Phrynosoma Wiegmann. 



Tympanic drum covered with scaly skin Anota Hallowell. 



Twelve genera of this family enter the nearctic fauna. But one of 

 tlieLse [Sceloporus) is found in its Eastern and Austroriparian districts, 

 while four are found in the Central [Sceloporous, Phrynosoma, Hol- 

 hrooTcia, Crotaphytus). The Pacific district includes four {Sceloporus, 

 Uta, Phrynosoma, Crotaphytus) ', while the remaining genera belong to 

 the Sonoran. Of these genera Phrynosoma and Sceloporus only occur 

 in the Mexican district of the neotropical realm. 



The geographical distribution of the genera is represented in the 

 accompanying table : 



