VERTEBRATES. 225 



originally noticed by Messrs. Newberry and Worthen. The original 

 specimen is probably that of an immature tooth which had not 

 been brought into use prior to the destruction of its possessor, and 

 it is owing to this fact that it presents merely the coronal crest or 

 shell entirely detached from the base, which was of a coarse porous 

 structure and less solidified than the layer more strictly pertaining 

 to the coronal region.; also to the same state of things is doubtless 

 attributable the very perfect state of preservation of the rugose 

 ornamentation, which in this instance occupies the entire coronal 

 surface. Fragments of teeth identical in contour and ornamentation 

 are readily identified with the above specimen ; but others bearing 

 unmistakable evidence of excessive abrasion while in use, present a 

 nearly plane coronal surface with only traces of the rugre remaining 

 in the more depressed portions of the surface. The latter, from the 

 general outline, apparent original contour, and the posteriorly gently 

 convex course of the transverse depressions which also correspond 

 with the lines of growth, strongly indicate their identity with the 

 original specimen, and it is with the aid of these maturer examples 

 that the outline of the form may be more definitely sketched, the 

 type specimen being imperfect at either lateral border. 



The type example is probably a representative of the form pro- 

 visionally identified with the upper jaw. The teeth attain medium 

 size, quadrilateral in outline. In more or less worn specimens, the 

 usual condition of the examples that have been found, the coronal 

 region presents a moderate longitudinal convexity, and a slight 

 transverse concavity, in which direction the surface shows a more 

 or less distinct undulation, the plane posterior slope preserving 

 traces of the original rugose ornamentation. The coronal surface 

 of unworn teeth, like the type specimen of the form, shows a rather 

 strongly arched contour from behind forward, produced by a con- 

 spicuous transverse ridge, from which the surface gently slopes 

 with slight concavity to the anterior margin, more steeply sloped 

 behind to a slight impressed angle, whence the surface presents a 

 nearly plane area of variable width, terminating in the posterior 

 margin, and irregularly undulated longitudinally; the crest of the 

 transverse ridge is gently sagged throughout the greater part of its 

 extent, and on nearing the outer ( ?) border it is somewhat steeply 

 sloped into what appears to have formed a shallow, narrow depres- 

 sion just within the outer coronal fold; even in worn examples the 

 latter conformation of the coronal surface is more or less discern- 

 ible, but the inner border is angularly rounded to the nearly ver- 



15 



