530 E. LTDEKKEK 01^ THE GENUS MICROCHCERtTS. 



great importance. In the cranium there are altogether nine teeth 

 on each side. The last three are true molars, in advance of which 

 are two molariform premolars ; the four teeth in front of the latter 

 are caniniform, and at least the two first are inserted in the pre- 

 maxilla. As the maxillo-premaxillary suture is not visible, it is 

 impossible to be sure of the homology of the third and fourth teeth ; 

 but the writer is inclined to regard them respectively as the third 

 incisor and the canine, although they may be the canine and the 

 antepenultimate premolar. The upper dental formula will be there- 

 fore either I. 2, C. 1, Pm. 3, M. 3, or I. 3, C. 1, Pm. 2, IT. 3. 

 The innermost incisor is separated by a wide interval from the 

 homologous tooth of the opposite side, in which respect it agrees with 

 Erinaceus and several other Insectivora, and differs widely from all 

 Ungulates. The small size of the canine (whichever this tooth be) 

 and the caniniform incisors are marked insectivorous characters. 



The lower jaw is reported to have been perfect when first discovered, 

 but was broken during a journey to Paris. In its present condition 

 it comprises the middle portion of the ramus, with the three true molars 

 and the last premolar ; but the two extremities have been restored 

 in wax ; the restoration of the anterior extremity is totally erroneous, 

 there being a huge canine, which could not possibly have belonged 

 to such an animal. In the figure there are shown three equal-sized 

 premolariform teeth in front of the true molars, then a very minute 

 tooth, and then a larger caniniform tooth with a considerable for- 

 ward inclination ; but it is uncertain whether this is correct. 

 Another portion of a right ramus in the Museum from the same 

 locality shows two premolariform teeth in front of the true molars, 

 and two empty alveoli in advance of the former, which incline forward 

 as in Erinaceus-, but it is not easy to determine their serial homology. 



The dentition of Microchoerus agrees so closely with that of 

 Erinaceus that the writer has no hesitation in placing it in the same 

 order. The cusps on the true molars are decidedly lower than, and 

 difffer considerably in arrangement from, those of Erinaceus, the 

 difference being so great as, in his opinion, to forbid the inclusion 

 of the two genera in the same family. The name Eyojysodus, if, 

 as is almost certainly the case, that genus be identical with Micro- 

 choerus, should be superseded by the latter ; and under any circum- 

 stances both the American and English forms must be placed in the 

 same family. Prof. Cope*, in discussing the affinity of Hyopsodus, 

 associates it with the lemurine Aclapis, but remarks that many of 

 the genera which he provisionally includes in the same group present 

 such marked resemblance to the Insectivora that he is unable to say 

 whether they should be referred to that order or to the Lemuroid 

 Primates, there being strong evidence of a complete transition be- 

 tween the two. 



The identity or, at least, the intimate affinity of Microchoerus and 

 Hyopsodus is another instance of the close connection existing be- 

 tween the Upper Eocene and Lower Miocene MammaUan fauna of 

 * Op. cit. pp. 459, 460. 



