277 



come into place and the enamel had been slightly worn along the summit of the 

 anterior ridge, the second molar showed the lobes worn down two thirds of the way 

 toward the valley. In the cast of the right maxilla with the dentine exposed on the 

 lobes of m 3, those of d * are worn down to the shallowest part of the valley. In the 

 oldest specimen of this species the grinding-surface of this tooth (ib. fig. 7, d 4) is reduced to 

 a smooth field of dentine (d) and osteodentine (0), with a peripheral boundary of enamel, e. 

 This dental constituent does not exceed a line in thickness at this stage of abrasion. 



The dentition of the upper jaw of Nototherium inerme is known to me by a portion 

 of that jaw with the right and left series of grinders and much of the intervening bony 

 palate ; but the premaxillaries and upper incisors are wanting, being broken away with 

 the contiguous part of the maxillary close to the molar (d 3) ; and both this and the 

 second molar (d 4) are mutilated on the left side of the jaw. The right series is repre- 

 sented of the natural size in figure 5, Plate XLIII. 



The first molar is relatively smaller and less complex on the grinding-surface than is 

 d 3 in Nototherium Mitchelli (ib. fig. 4) : the transverse and antero-posterior diameters 

 are alike. The outer lobe or division has one coronal prominence upon which a slender 

 triangular tract of dentine is exposed extended antero-posteriorly ; a more equal-sided 

 triangular tract is exposed on the shorter inner lobe ; an anterior and a posterior basal 

 ridge bound corresponding depressions divided by the confluence of the apices of the 

 outer and inner divisions at the centre of the crown ; a short external basal ridge closes 

 the concavity impressed upon the hind half of the outer surface of the crown. One 

 cannot distinguish, with certainty, the worn enamel from the dentinal tracts in the 

 plaster cast of the answerable tooth of Nototherium Mitchelli ; nor do the photographs 

 help in this particular ; but both concur in demonstrating the differences of size, shape, 

 and proportion of the anterior molar, which I judge to exceed those allowed to sexual 

 or individual variation, without affording ground for inferring generic distinction from 

 the modifications of d 3, represented in Plate XLIII. 



The more constant teeth (d *-m 3) in figure 5 exemplify the Nototherian characters 

 with the inferiority of size, corresponding with the little that is known of the present 

 species. Nototherium inerme, like Not. Mitchelli, has the hind lobe of the last molar 

 contracted in breadth, and the antero-posterior extent of the crown is less than that in 

 the opposing molar (ms) of the lower jaw. 



A greater proportion of the enamel of this worn grinder, in the subject of fig. 5, 

 Plate XLIII., shows the punctate rugous character than in the antecedent teeth. 



The specific character of Nototherium inerme is well exemplified by the minor rela- 

 tive size of the anterior molar, d 3 (Plate XLIII. fig. 5), of the upper jaw, as by that of 

 the incisor in the lower jaw. 



Of the dentition of this jaw, I commence the description with those in that of the 

 immature specimen of Nototherium Mitchelli (Plate XL.), consisting of the right 

 ramus of the mandible with the first three molars in place, the germ of a fourth, and 

 part of the formative cavity of a fifth molar. The tip of a procumbent incisor projects 



