216 PALEONTOLOGY OF ILLINOIS. 



growth, instead of presenting the forward curvature or moderate 

 concavity characteristic of perfect teeth. The anterior margin, also, 

 shows an accurate outline, with auriculations at either angle, which 

 may be attributable in part to wear from the severe usage to which 

 the teeth were subjected during the life of their possessor. The 

 backward curvature of the lines of growth, which appear to be in- 

 dicated by alternating belts slightly varying in density and hardness, 

 are the same as above remarked in the maxillary form. 



It is a singular, not to say extraordinary, circumstance that none 

 but left-side individuals of the supposed maxillary form and right- 

 side teeth of the mandible exist in the collections, which contain a 

 score and a half of specimens in all conditions of preservation. 

 Supposing the teeth to have been ranged in double rows upon the 

 jaws, the impingement of individuals of opposite rows at their 

 oblique articular inner borders gives to the transverse section a 

 marked concavity, while the inbeveled apparent obliquity of the 

 anterior and posterior margins indicate a considerable fore and aft 

 arching in the coronal contour of the series of maxillary teeth. The 

 individuals of the opposed mandibular form, viewed in the same 

 relative position, present contour diametrically opposite to those 

 noted in relation to the maxillary series, the transverse section of 

 the double row showing a convexity conforming to the concavity of 

 the opposed series, though the longitudinal arching of the series of 

 the latter form was perceptibly less than that of the mandibular 

 series. The latter observations apply to the small and medium size 

 teeth, but in the large mature teeth the longitudinal convexity of 

 the crown seems to be more pronounced, which would give to the 

 series of teeth upon the jaw a greater relative convexity from be- 

 hind forwards. However, it will have become apparent, that there 

 is intimate correspondence in the coronal contour and co-adapta- 

 tion of triturating surface in the two forms here associated under 

 the same specific designation. And, however large the materials in 

 our possession, it is hardly more than suggestive of the complete 

 history of the species they represent. 



An imperfect tooth from the same formation at Grand Eapids, 

 Michigan, kindly submitted to us for examination by Prof. E. A. 

 Strong, appears to be intimately allied to the present species. The 

 specimen is also a left-side tooth of the mandibular form, from 

 which the enamel layer has been exfoliated, revealing a beautiful 

 punctate surface quite in contrast to that usually prevalent in the 

 teeth derived from Missouri and Illinois localities. The medullary 



