DAKOTA AND NEBRASKA. 213 



An additional specimen, of about the same size as the preceding, but more blunt 

 at the apex from abrasion, has the same form, but has the basal ridge undeveloped 

 externally. 



Another specimen, consisting of the crown of a canine tooth, is supposed to belong 

 to the upper jaw of Titanotherium. It is larger than the crown of the supposed lower 

 canines, and is devoid of a basal ridge. It further differs in the course of the sub- 

 acute ridges defining the inner and outer surfaces, which descend nearly straight 

 from the apex in the lower canines, but in the upper one curve inward and towards 

 each other approaching the base. The apex of the specimen is worn off horizontally, 

 and presents a lenticular excavation of the dentine bordered by enamel. The length 

 of the specimen in its present condition externally, where greatest, is seventeen and 

 a half Hues; the antero-posterior diameter of the crown is fifteen lines, and the trans- 

 verse diameter thirteen and a half lines. 



An additional specimen consists of the greater portion of an unworn crown of a 

 canine tooth of the same shape as the former, but of less size. Its length externally 

 is sixteen and a half lines. 



Incisors. — As previously indicated, the upper jaw specimen of Titanotherium, figux'e 

 1, plate XXIV, in Prof Hall's collection, proves the existence of a pair of incisor 

 teeth on each side, but, with the exception of a single fang, the alveoli only are pre- 

 served. The alveoli are close to the canines, and those of the two sides are separated 

 by a transverse concave notch about half an inch in width. The alveoli are antero- 

 posteriorly oval, and neai-ly equal in size. 



Structure of the teeth. — The teeth appear devoid of coronal cementum. The enamel 

 is fi'om the fourth of a line to a line and a half in thickness, and, taking into \'iew 

 the size of the teeth, is comparatively smooth. Upon the outer sides of the molars it 

 is more or less finely corrugated, and marked by contour lines of growth. Moderate 

 abrasion or friction appears comparatively early to have made the surfaces smooth 

 and highly polished. In the fossils the enamel is stained steel-gray, and in many 

 positions exhibits a high polish. 



Upper maxillary and intermaxillary hones. — The upper jaw specimen of Titanothe- 

 rium, of Prof Hall's collection, consists of small fragments of the alveolar portions of 

 the maxillaries and the greater portion of both intermaxillaries. The latter are co- 

 ossified with the former, and the course of the intervening suture is obliterated. 



The intermaxillaries project but little in advance of the position of the canine 

 alveoli. The front of the snout, in advance of the lateral convex prominences pro- 

 duced by the latter, presents a broad slope about four inches in width and three in 

 depth below the inferior concave nasal border. The nasal orifice was about three 

 inches in width. 



