76 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 9i 



in 5 mm., wlier'eas in the type dentary eight teeth occupy a similar 

 space. The teeth of both upper and lower series decrease in size 

 toward the front, and the transversely compressed crowns of the 

 lateral teeth change to simple, rounded, sharp-pointed teeth in front. 

 The dental formula of Exostinus serratus may now be stated as 

 follows : 



Maxillary 14+premaxillary 8 __36 

 dentary ir ~28^ 



This genus and species were tentatively referred in my 1928 review 

 of the lizards of North America to the family Iguanidae. Although 

 this new material contributes but scant information on this important 

 question, the subequal size of the pleurodont teeth, the constantly 

 long cylindrical shafts, and the gradual change taking place between 

 the lateral and anterior teeth are all features in accord with its as- 

 signment to the Iguanidae. The osseous ornamentation of the skull 

 is highly suggestive of the horny tubercular ornamentation of the 

 PhrynosoTna skull. For the present, therefore, Exostinus will be 

 regarded as an extinct representative of the Iguanidae. 



V. S. eOVERNMENT PRINTING OfFICEi 1141 



