YEETEBBATES. 349 



the concave face is but slightly depressed vertically, averaging iu width 

 about one-third greater than the opposite face, which iu the majority of 

 specimens is also depressed vertically on either side of the principal 

 cone — in rare examples the angle of the median cone is much distended, 

 producing a broad convexity in the median region of the narrow face; 

 coronal belt well-marked, consisting of three or four imbrications in the 

 concave face, and three in the opposite border, generally regularly dis- 

 posed throughout the median region, but often interrupted by interca- 

 lated folds on reaching the extremities — in some instances the uppermost 

 fold terminating in the acutely angular buttress of the median cone. 

 Base forming a strong plate, considerably narrower than the crown, the 

 narrow face beveled to the angularly-defined, flattened inferior surface, 

 and about half or two-thirds the hight of the face beneath the convex 

 crown-face, which latter equals the greatest depth of the base. In worn 

 teeth the crest is more or less reduced in elevation, the median cone is 

 almost always truncated and frequently worn down to the level of the 

 lateral portions of the crest ; coronal surfaces smooth or faintly undu- 

 lated, and polished ; basal region more or less roughened. 



"We have recognized a variety differing from the above by their more 

 slender proportions, and linear or slightly curved outline, relatively 

 inconspicuous and eccentric median prominence, the crest being remark- 

 ably uniform throughout, the coronal belt containing an additional fold. 

 Lateral diameter of crown .54 inch, antero-posterior diameter .11, ele- 

 vation about .05. A third variety is distinguished by its relatively 

 short lateral diameter, and strongly arched vertical outline, and the 

 predominance of the concave crown face over convex face in vertical 

 hight; the lateral portions) of the crest are faintly denticulated, the 

 median cone sometimes flattened in the convex face, the coronal belt 

 showing three folds in the concave and two in the opposite border, 

 where they are sometimes interrupted, presenting a beaded appearance. 

 Lateral diameter of crown .30 inch, lesser diameter about .12, or equal 

 to the depth of the concave face, hight of median cone in the convex 

 face about .07 inch. 



The differences which distinguish the several varieties noticed above 

 one from the other are not sufficiently characteristic to be deemed of 

 specific importance, and probably indicate no greater difference than 

 that dependent on the position the teeth occupied upon the jaws. The 

 first variety probably held a median position, the third occupying the 

 anterior portion, and the second variety may have filled the intermedi- 

 ate space, or, perhaps, more probably the posterior portions of the jaws. 



However variable these teeth may appear on casual examination, a 

 more intimate acquaintance derived from the comparison of a large 

 suite of specimens reveals a remarkable identity of features common to 



