VERTEBKATES. 121 



defined by a narrow channel from the downward and outward pro- 

 jecting basal portion, which terminates in a thin rim inferiorly, the 

 axes of the channel showing relatively coarse pits ; postero-lateral 

 border with a moderate sigmoidal curvature, diverging posteriorly 

 at an angle of 50 with the opposite border terminated in the 

 acutely rounded posterior angle, coronal fold equally sharply de- 

 fined from the basal portion, which is more or less expanded 

 toward the posterior extremity where it forms a wide platform 

 extending beyond the limits of the coronal border, the channel 

 similarly marked by a row of large vascular pits ; general direction 

 of inner margin nearly at right angles to the antero-lateral border, 

 broadly arched round the base of the median prominence, and 

 again gently curved sigmoidally in passing to the posterior ex- 

 tremity; coronal region defined by an abruptly inbeveled narrow 

 fold from the deep basal area which terminates inferiorly in a very 

 thin edge; surface irregularly and coarsely marked by vertical 

 rugosities and sulci ; usually, however, the attenuated rim is 

 broken away, and the margin abruptly inbeveled. Coronal contour 

 strongly arched in the direction of inrollment; anterior belt well 

 defined from the median prominence, slightly, sometimes strongly, 

 arched transversely, with a slight furrow along the anterior edge in 

 well preserved examples ; median prominence occupying half the lateral 

 diameter of the crown, strongly and regularly arched transversely, 

 the rounded axis lying a little anterior of the middle, the broader 

 slope descending into the posterior depression where it is defined 

 by a marked angulation; posterior alation proportionately wider 

 than the anterior plane belt, faintly depressed in the middle and 

 slightly arched transversely along the moderately upraised postero- 

 lateral border, where the edge of the coronal enamel is inbeveled 

 similarly to the enamel fold along the antero-lateral border, and 

 rounded at the extremity. Along the inner margin of the well pre- 

 served tooth the surface is invested in a dense semi-opaque enamel 

 through which the extremities of the tubular structure are faintly 

 outlined; in worn surfaces, this same structure produces a minute, 

 rather widely spaced punctuation, of which there are about 30 

 pores in the space of a square millimetre. Greatest transverse 

 diameter of the crown of a medium-size example across the inner 

 margin 15 mm., or to the extremity of the basal spur 17 mm.; 

 length of antero-lateral border to point of inrollment 10 mm. ; 

 greatest depth ditto, 1.5 mm. ; length along postero-lateral border 

 to the inrolled outer margin 10 mm. 



