INSECTIVOEA. 203 



a notch on the inner side. Last lower molar with this anterior ti-ansverse 

 triangle, a diagonal ridge, and a heel with raised border. The fourth premo- 

 lar has a V-shaped crest on its anterior half, the angle being an elevated 

 apex of the external face, the limbs descending inward. 



This genus diffei's from AncMppodus and Ectoganus in the far less gliri- 

 form character of the incisor teeth, although the composition of the molar 

 teeth exhibits a true resemblance to that seen in those genera. The incisor 

 is annectant to the form usual in Mammals, betraying the rodent character 

 in the absence of enamel from the posterior face, and the oblique bevel 

 posteriorly from the apex to the shank. The ? canine or superior incisor 

 (second form) is elongate, and without distinction between crown and root, 

 but is straight, and not gliriform. A resemblance to the superior incisor of 

 Ectoganus can be observed in the deep emargination of the enamel to near 

 the apex on the inner side, and the convexity of the opposite side. 



A strong resemblance can be discovered between some characters of 

 this genus and Totnitlierium, which is described under the Mesodonta. The 

 composition of the inferior molars in the latter is essentially the same in the 

 two genera, but the anterior cusps and yokes are relatively less developed 

 in Tomitherium. An obvious resemblance is seen in the last premolar, 

 which is somewhat sectorial in the form of its anterior half in both genera. 

 There is no enlarged external incisor in Tomitherium, but either arrange- 

 ment is consistent with mesodont aflfinities, and even incisors of rodent-like 

 character, in view of the structure of Chiromys. Its resemblances to Eri- 

 naceiis are, however, so many that I leave it in the neighborhood of that 

 genus. The premolars of the superior series are nearly alike in the two 

 genera, and so are the inferior molars, excepting the last, which is much 

 smaller in Erinaceus. The superior molars of the hedge-hogs only differ 

 in the development of the posterior cingulum into a posterior internal cusp, 

 which is connected with the posterior external cusp by a transverse ridge. 



It is probable that this genus represents the group ancestral to the 

 existing Erinaceidoe. 



