804 THE WHITE RIVER PAUFA. 



Tupaia, Talpa, Sorex, &c., there are two of the middle series, as in Pera- 

 therium, and these add a strong internal lobe also. In Erinaceus and Gym- 

 mora they are quadrituberculate. The closest approximation is made by 

 the g-enera Mystomys and Solenodon, the former African, the latter West 

 Indian. In these the external cusps are present; there is but one well- 

 developed median, and in the latter the internal is quite reduced. The 

 molars of Mesodedes thus resemble most closely those of Solenodon (Brandt), 

 but the external cusps are more developed than in that genus. Among the 

 Eocene genera, the greatest resemblance is to be seen in the genvis Delta- 

 therium. The internal cusp of Mesodedes is connected with the external 

 ones by oblique ridges, as in Delthatheriwn ; and on one of these is a rudi- 

 mental tubercle, representing an intermediate cusp. The dentition of the 

 lower jaw is quite different in Deltatherium in the simple last premolar, and 

 cutting last true molar. 



In the lower series the form of the true molars is not unlike that of 

 several diverse recent genera. It is quite unique in its large four or five 

 cusped last premolar, which has some resemblance to a modified sectorial. 

 The nearest approach to it which I can discover among recent genera is the 

 Madagascar Galeopithecus. 



In respect to the remainder of the skeleton, numerous characters dis 

 tinguish it from the Centetidce (which includes Solenodon) and the Mysto- 

 myidce. Both of these lack the zygoma, which is present in Septididce, and 

 have the nasals coossified, while they are distinct in these tertiary forms ; 

 Mystomys, further, lacks the clavicle. The pi'esence of the zygoma without 

 postorbital processes is a point of resemblance to Erinaceus, but the strongly 

 keeled presternum and absence of cervical neural spines are found elsewhere 

 in the Talpidce. In the presence of the humeral arterial foramen, it again 

 differs from Erinaceus and resembles other forms of the order. 



Comparisons with the Marsupialia are chiefly to the DidelpMdce. The 

 superior molars are much like those of Didelphys, the inner cusp of the 

 third premolar being a point of difference not seen, however, in the allied 

 Leptidis. The latter, according to Leidy, has only two superior incisors on 

 each side, a wide divergence from the opossums. In the inferior molars the 

 absence of the anterior inner cusp is a strong mark of distinction. The 



