20 PROCEEDINGS OF THE ACADEMY OF 



that indicated by Prof. Marsh under the name of Lophiod 'on nanus. 

 One of the specimens was obtained, by Dr. Joseph K. Corson, 

 U.S.A., at Grizzly Buttes ; the other, by Dr. J. Van A. Carter, at 

 Lodge-pole Trail, Wyoming. In both these the molar series is 

 six, and the last molar has a bilobed crown. In the upper jaw 

 specimen referred to Lophiodon nanus by Prof. Marsh, there are 

 seven molars. One less in the lower jaw may be regarded as a 

 less important character than the others separating Hyrachyus 

 from Lophiodon, in which view I refer the specimens to the former 

 under the name of Hyrachyus nanus. Probably also the other 

 species which have been noticed under the names of Lophiodon 

 7nodesfus. L. affinis, and L. pumilus, may be viewed as pertaining 

 to Hyrachyus. 



I further exhibit portions of jaws of several individuals of a 

 small pachyderm allied to Hyopsodus. The specimens were dis- 

 covered, by Dr. J. Van A. Carter, at Grizzly Buttes and Lodge-pole 

 Trail, Wyoming. 



In Hyopsodus, seven molars, a feeble canine, and the incisors 

 together form an unbroken row. In the lower jaw specimens, 

 which I propose to refer to a genus with the name of Blicrosyops, 

 six molars, a comparatively large canine, and the incisors form 

 the corresponding series. 



In Hyopsodus, the lower true molars, except the last one, are 

 of uniform width at the fore and back part of the crown. In 

 Microsyops the fore part of the crown is decidedly narrower than 

 the back part. In both genera the crown of these teeth is com- 

 posed of an outer pair of demiconoidal lobes with crescentoid 

 summits and an inner pair of conical lobes. In Hyopsodus the 

 contiguous horns of the crescentoid summits of the outer lobes 

 conjoin in the antero-internal lobe, and the anterior horn of the 

 crescentoid summit of the antero-external lobe ends at the base 

 of the antero-internal lobe. In Microsyops the anterior horn of 

 the crescentoid summit of the antero-external lobe ends in a tuber- 

 cle in front of the antero-internal lobe, while its posterior horn 

 ends in the latter; but the anterior horn of the postero-external 

 lobe, instead of joining the antero-internal lobe, as in Hyopsodus, 

 ends at the base of the antero-external lobe. The character of 

 these teeth leads me to the belief that the jaw specimens referred 

 to Microsyops belong to the same animal as that named Hyopso- 

 dus gracilis by Prof. Marsh, and with this view I propose the 

 name of Microsyops gracilis, which may be used in either case, 

 whether the animal is or is not the same as Hyopsodus gracilis. 



Two additional specimens I suppose belong to an insectivorous 

 animal, though they may perhaps indicate a small marsupial. 

 They were obtained, by Dr. Carter, at Lodge-pole Trail, Wyoming. 

 One of the specimens, an upper jaw fragment, contains a molar 

 tooth. This resembles the back molars of the Opossum, but with 

 the outer lobes of the crown proportionately better developed, and 



[April 16, 



