778 THE WHITE RIVER FAUNA. 



portions of the skeleton. The genus was founded on the supposition that the 

 typical species, the P. cohradoensis, possesses the zygosphene articulation, 

 a character which I have since been unable to verify, and do not now 

 believe in. The subtraction of this character leaves little for the genus to 

 stand on ; but I retain the name with the following definition : 



Vertebral centra with the articular faces much depressed, and without 

 inferior or lateral carinse. The ridge connecting the zygapoph3'ses deeply 

 incised. Neural spine a low keel. 



The incised interzygapophysial ridge distinguishes these vertebrae 

 from those of Peltosaurus. 



The two best known species may be distinguished as follows : 



Much smaller ; ueural spine not ending in a knob; costal articular face principally 

 convex P. cohradoensis. 



Much larger; neural spine ending in an obtuse apex posteriorly; costal articulation, 

 superior part concave P. rhamhastes. 



A third species is only known from a sacral vertebra. 



Platyrhachis coloradoensis Cope. 



Locis citaiis. 

 Plate LX; fig. 17. 



The inferior face of the centrum in four dorsal vertebrae is plane, and 

 is separated by an obtuse right angle from the nearly vertical lateral sur- 

 faces. Neural arch depressed, an angle connecting the zygapophyses. 

 Neural spine a keel, projecting beyond the posterior margin in a mucro. 

 Ball truncate below its convex face, looking sliglitly upward. Costal 

 capitular surface semiglobular, directly below the anterior zygapophysis. 

 Neural arch concave between zygapophyses. 



Measurements. 



M. 



Length of three dorsal vertebrie 0.0070 



Length of one dorsal vertebra 0028 



„• ,. j-i 1, < transverse 0014 



Diameter ol ball < . , „.„. 



< vertical 0006 



Elevation of vertebra 0019 



Width betvfeen zygapophyses 002,') 



This species is of small size, not exceeding the red salamander (Si)elerpes 

 ruber) in dimensions. 



From Horse Tail Creek, Northeastern Colorado. 



