85 



part of the coronoid process terminates in a tubercle at the fore part of the 

 moderately deep masseteric fossa.' 



Another foramen, perhaps not constant to the species, is situated below 

 the position of the fore part of the first molar. 



The measurements of the specimen are as follows: 



Lines. 



Depth of jaw below last molar 4f 



Depth of jaw below last premolar '. 4£ 



Space occupied by last premolar and molars 7£ 



Space occupied by the molars '. 6 



Breadth of penultimate molar * 2J 



Breadth of last molar 2\ 



The only specimen of an upper tooth which may, with any probability, be 

 supposed to belong to Microsyops, is contained in a small fragment of the 

 jaw, found by Dr. Carter on Dry. Creek. The tooth, apparently a first/ or 

 second molar, is represented in Figs. 19, 20, Plate XXVII. The crown is 

 not so square and is proportionately of less breadth fore and aft than in the 

 corresponding tooth of Hyopsodus. It narrows inwardly more than in the* 

 latter, the reduction taking place posteriorly, where the crown is concave. 

 The constitution of the tooth is nearly as in Hyopsodus, and the principal 

 difference is found in the condition of the postero-internal lobe. In Hyopso- 

 dus, this is a reduced form of the lobe in advance, being crescentoid. In the 

 supposed tooth of Microsyops, the postero-internal lobe appears as a conical 

 tubercle springing from the base postero-internally of the larger crescentoid 

 lobe in front. In Hyopsodus, the postero-median lobe is a simple cone, but 

 in the tooth in question it is pyramidal. 



The antero-posterior diameter of the crown externally is 1.6 lines ; inter- 

 nally, 1.2" lines; the transverse diameter anteriorly is 2.2 lines. 



Undetermined. 



Fig. 12, Plate VI, represents a specimen found by Dr. Carter on Henry's 

 Fork of Green River. It consists of a lower-jaw fragment with the last pre- 

 molar and the fangs of the molars of a mature animal of undetermined 

 character, but, from the form of the remaining tooth, evidently allied with 

 Hyopsodus. The premolar, Fig. 13, is unlike the corresponding one of the 

 latter genus, as seen by comparing it with Figs. 5 and 8, but resembles the 

 true molars. Suspecting that it might be a last temporary molar, notwith- 

 standing its slightly worn condition and its association with the full series of 



