DAKOTA AND NEBRASKA. 345 



INSECTIVORA. 



This oi'der, in the extinct mammalian fauna under consideration, is represented by 

 the remains of two genera, which were discovered by Dr. Haydeu in his last trip to 

 the Mauvaises Terres, in the summer of 1866. The fossils belong to bed B of the 

 miocene formation of Dr. Hayden's sections. Both genera indicated by the fossils 

 are extinct, and have been named Leptictis and Idops. Both are nearly allied, and 

 belong to a peculiar family related with that of the Hedgehogs. 



LEPTICTIS. 



Leptictis Hatdeni. 



The animal for which this name has been proposed is indicated by an almost com- 

 jjlete skull, obtained near the mouth of one of the small tributaries of White River, 

 in the Mauvaises Terres. It apparently belongs to an animal of the insectivorous 

 order, but exhibits sufficient resemblance to the skulls of the Opossums to lead to the 

 suspicion that it may possibly pertain to a member of the Marsupialia. Among the 

 Carnivora it exhibits more affinity to the canine family than any others, and appears 

 more nearly related to the Viverrine than the Musteline family. 



The skull is without the lower jaw, and was imbedded in the soft silico-calcareous 

 rock of the tertiary beds of White River. The matrix adhered the more intimately 

 to the fossil through the intermediation of a thin layer of more ferruginous character. 



The skull belonged to an animal past maturity, as indicated by the blunted or 

 worn condition of the teeth ; it nevertheless retains most of the sutures as distinctly 

 as in the Opossums. 



The specimen, represented in figures 25, 26, 27, plate XXVI, is less in size than 

 that of the Mink, and its shape is more Canine than Musteline. It bears some re- 

 semblance in form to that of the insectivorous genus Olisorex, or to that of the viver- 

 rine genus Eujjleres. 



The cranium is remarkable for the possession of a pair of prominent ridges defining 

 the ujjper part of the temporal fossa?, as in a fossil cranium rejjresented by De Blain- 

 ville (Osteographie, Mustela, plate xiv) under the name of Mustela plesictis from 

 Auvergne, and by Gervais (Paleoutologie Francaise, plate xxviii, figure 2) under the 



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