114 PALAEONTOLOGY OF ILLINOIS. 



punctation also agrees. The present form is represented by half a 

 dozen or so imperfect specimens, which, while they are readily 

 recognizable, are insufficient for comparative measurements showing 

 their proportionate dimensions, a mature example having a trans- 

 verse diameter across the inner margin of 12.5 mm. 



Maxillary posterior teeth corresponding in dimensions with the 

 posterior form of the mandible, presenting the general outline 

 ascribable to this form, moderately arched longitudinally and strongly 

 inrolled along the outer margin. Antero-lateral border slightly 

 oblique to a right line connecting the inner angles, presenting a 

 channeled basal rim defined above by the narrow inbeveled fold of 

 coronal enamel; postero-lateral border approaching point of inroll- 

 ment at an angle of 60, and less, to the opposite border; inner 

 margin broadly arched round the base of the posterior lobe, in 

 front of which it is sharply contracted and thence continued in a 

 slightly concave course to the anterior prominence, round which it 

 makes a broad curve terminating in the obtuse anterior angle. The 

 definition of the anterior and posterior regions of the crown is 

 marked; posterior lobe occupying apparently less than half the 

 lateral diameter of the tooth, broad posterior slope gently and 

 regularly arched transversely, in front steeply sloping from the 

 sharply rounded crest to the angulation forming its anterior limit; 

 the surface of the relatively wide depressed median belt gently 

 rises into the summit of the anterior lobes, which latter usually 

 presents a more or less well-defined, narrow, rounded ridge, some- 

 times two or more obscure ridges, in part occupying the moderately 

 abrupt slope along the antero-lateral border; in some examples 

 faint revolving ridges extend over the depressed median belt, and 

 in others obscure impressed lines may be traced in the wide slope 

 of the posterior lobe. In the perfect state the entire coronal sur- 

 face was occupied by transverse rugae parallel with the inner 

 margin and more or less so to one another, though in the latter 

 respect exhibiting considerable variation in the broken continuity, 

 bifurcation, and implantation of the rugae, which have the same 

 appearance as in the preceding forms mentioned above. Toward 

 the outer margin and indeed over the middle portion of the crown 

 where its surface was subjected to greatest attrition while in use, 

 the rugai are obsolete or nearly so, though in some instances still 

 traceable in the disposition in transverse lines of the more or less 

 elongated or confluent punctae, which are conspicuously displayed 

 over the entire surface save along the inner margin where the 



