LACERTILIA. 777 



This species is about the size of our Cnemidophori. From all the genera 

 of this group, Aciprion differs in the uniform character of the teeth, there 

 being no simple teeth in the front of the series so far as preserved. A jaw- 

 fragment probably represents a second species of this genus. A well-pre 

 served lower jaw of the Aciprion formosum was obtained in Dakota by the 

 Princeton Expedition of 1882. 



DIACIUM Cope. 



Synopsis New Vertebrata Colorado, 1873, p. 17. Annual Report U. S. Geol.Surv. Terrs., 1873 (1874), 



p. 514. 



This genus was originally established on the sacral vertebra of a liz- 

 ard which displayed the peculiarity of the absence of any trace of neural 

 spine. 



The diapophysis is subcylindric and elongate. Centrum concave 

 below ; neural arch flat above. Articulation without zygosphene or rudi- 

 ment of it ; zygapophyses oblique, the arch deeply excavated between the 

 anterior ones. Obliquity of ball inferiorly. 



DiACIUM QUINQUIPEDALE Cope. 



Loda citatis. 

 Plate LX; fig. 20. 



Two obscure hypapophysial tubercles below the ball. Centra slightly 



depressed, the cup excavated above and below. An angulation extends 



backwards from each anterior zygapophysis; the neural arch between them 



flat on the anterior half 



, Measurements. 



M. 



Length of centrum below 0.0100 



^. . J. .■ I < transverse 0086 



Diameter of articular cup ■; . . , ,„^ , 



( vertical 0064 



Diameter of base of diapophysis 0044 



Width between anterior zygapophyses 0098 



Width of upper plane of neural arch 0078 



This species is as large as any of the existing species of Iguanidce. 

 PLATYRHACHIS Cope. 



Synopsis New Vertebrata Colorado, 1873, p. 19. Annual Report U. S. Geol. Surv. Terrs., 1873 



(1874), 516. 



This genus is known only from vertebrae, which, though abundant 

 in the White River beds, I have been as yet unable to connect with other 



