135 



the meatus is isolated, and not continued into a ridge, except externally, where 

 it gives rise to the heavy ridge which extends to the base of the great ala. 

 The vertebrae- exhibit round articular surfaces ; those of the dorsal region 

 being rather stouter than the cervical, though the difference does not appear 

 to be so marked as in the preceding species. The anterior caudals possess 

 wide diapophyses. The articular faces are a vertical oval, a little contracted 

 above, sometimes by a straight outline. They preserve a peculiarly elongate 



form. 



Measurements. 



M. 



Lengtb of the axis (alone) • 0. 000 



Diameter of the ball, vertical 0.027 



Diameter of the ball, horizontal 0. 027 



Lenst.li of a posterior dorsal 0. 0G9 



Diameter of the ball, vertical 0.033 



Diameter of the ball, transverse 0. 03d 



Length of the caudal with the flat diapophysis , 0. 033 



Depth of the cup of the caudal 0. 031 



Width of the cup of the caudal 0.030 



Length of the mandible (28 inches) 0.720 



Depth at the coronoid process 0. 150 



Depth at the proximal end of the deutary 0. 074 



Depth at the distal end of the dentary 0. 020 



A fine specimen of this species was found by Martin V. Hartwell near 

 Fossil Spring; and portions of a second were found by Lieut. James H. 

 Whitten, on a bluff on Butte Creek, during my expedition of 1871. 



a a. The frontal bone without median keel: 



Clidastes planifrons, Cope. 



A large species, represented by large portions of the cranium, including 

 cpiadrate bone; by cervical and dorsal vertebrae, and fragments of other ele- 

 ments, all belonging to one individual. They are well preserved, and have 

 suffered but little from distortion. 



The frontal bone is especially massive, and is plane on the superior 

 surface. The superciliary borders are strongly concave, a feature either little 

 or not at all marked in other species known to me. It is thickened; but the 

 fossa for the postfrontal bone extends far toward the front and middle on the 

 inferior surface. In front of the prefrontal angle, the frontal contracts, nar- 

 rowing regularly to the line of the nares. The prefrontal has the remarkable 

 form characteristic of Clidastes stenops ; that is, with the exposed face subver- 

 tical or steeply roof-shaped, instead of horizontal. A groove descends on 



