VEKTEBRATES. 113 



nounced and quite persistent in their uniformity. Median ridge 

 rising into a rather sharply rounded crest nearly median in posi- 

 tion, the anterior slope moderate and slightly concave transversely, 

 terminating in a shallow depression bordered by a very narrow fold 

 immediately along the antero-lateral border; posteriorly the surface 

 abruptly descends into the depression on that side, whence the 

 alate expansion gradually rises with slight transverse concavity into 

 the moderately elevated postero-lateral border. The coronal surface 

 is quite regularly marked by transverse rugae parallel with the 

 inner margin, the interspaces nearly a millimetre in breadth and 

 rising from below upward producing a reversed imbricated appear- 

 ance. The ornamental rugae are most distinct over the depressed 

 areas ; in the more elevated exposed portions of the surface they 

 are usually obsolete; however, there are traces of their presence 

 over the entire area of the coronal region. The punctate structure 

 presents the usual appearances associated with teeth whose coronal 

 surface is traversed by transverse ridges and furrows, the punctae 

 being elongated usually in the direction of inrollment along the 

 transverse folds ; exfoliated and worn surfaces showing a relatively 

 minute, crowded punctation. Transverse diameter at the inner 

 margin of a medium-size tooth 20 mm. ; length of antero-lateral 

 border to point of inrollment 10.5 mm. 



Mandibular median tooth of proportionate size in relation to the 

 posterior form, trapezoidal in outline, elongated in the direction of 

 inrollment. Postero-lateral border nearly straight, opposite border 

 converging toward the outer extremity at an angle of about 20, 

 inner margin very oblique with a slight sigmoidal curvature from 

 the sharply rounded posterior angle to the obtuse anterior angle. 

 Coronal ridge situated posterior of the median line, of moderate 

 prominence and breadth, posterior slope abrupt and deep to the 

 narrow furrow close along the postero-lateral border, over which the 

 coronal enamel forms a narrow inbeveled fold ; anterior declivity 

 nearly equally steep but of less depth, denned by a rounded angu- 

 lation whence the surface more gently descends with slight trans- 

 verse convexity to the antero-lateral border just within which lies a 

 shallow parallel furrow recalling that adjacent the articular border 

 of the terminal tooth. Along the posterior border and over a large 

 part of the anterior slope the surface preserves the parallel, rarely 

 bifurcating transverse rugae, conforming to the direction of the inner 

 margin, and spaced as previously noted in relation to the last 

 described form, with which the general character of the surface 



