NO. 7 EARLY CENOZOIC VERTEBRATES — FRIES ET AL. 9 



the plateau through Oligocene time, just as strong movements con- 

 tined through Oligocene time in the coastal country. 



The fossil discovery also indicates that the great bulk of the vol- 

 canic rocks in the central part of the Mexican plateau are probably 

 of late Oligocene and Miocene age, for these rocks are conformable 

 with the upper part of the red conglomerate and are separated by 

 strong faulting and a period of erosion from the next younger rocks, 

 which are conglomerates and fine elastics known to be of middle and 

 late Pliocene age. The great masses of tin-bearing rhyolite distributed 

 over the plateau region of Mexico, as for example to the northeast 

 of Guanajuato city, are almost surely of Miocene age rather than of 

 Pliocene age as generally presumed up to now. The discovery will 

 help to determine the age of faulting, intrusion, and metallization in 

 many of the mining camps in the plateau country of Mexico. 



Class REPTILIA 



Order Squamata 



Family IGUANIDAE 



PARADIPSOSAURUS Fries, Hibbard, and Dunkle, new genus 



Genotype. — Paradipsosaiirus mexicanus. 



Diagnosis. — Skull elevated and of broad, robust construction. 

 Snout deep without prominent nasolachrymal cristae ; and external 

 nares opening forward. Parietal plate broad with only shallow lateral 

 embayments by the wide supratemporal fossae. Pineal foramen in 

 advance of the parietofrontal suture. Postf rontal small but distinct ; 

 postorbital with long, ventrolateral expansion ; and maxillary longer 

 than deep and excluded from contact with the frontal by articulation 

 between the nasal and prefrontal. Coronoid projecting high above 

 the dorsal margin of the mandible and, in lateral aspect, with both 

 the anteroventral and postero ventral angles somewhat produced. 

 Splenial extended forward to the symphyseal region and completely 

 covering the Meckelian groove. Dentition pleurodont; individual 

 teeth relatively large and few in numbers ; each with a laterally situ- 

 ated, longitudinal cutting edge, which is vertically wrinkled but non- 

 cuspidate, and with the crown slightly widened transversely. 



PARADIPSOSAURUS MEXICANUS Fries, Hibbard, and Dunkle, new species 



Diagnosis. — The same as for the genus (the only species). 

 Type. — U.S.N.M. No. 20667, skull and lower jaws, both lacking 

 the anterior and posterior extremities, collected in October 1952 by 



