MYOMOEPHA. 865 



In the mandibular rami the inferior masseteric ridge extends to below 

 the anterior border of the first molar, and is very prominent and acute. It 

 results that both the exterior and inferior aspects of the ramus are concave 

 to the anterior extremity of the crest, which slopes upwards. The incisive 

 alveolus, though not prominent, as in Hystricomorpha, is on the inner side of 

 the base of the ramus in front. Above the alveolar prominence the inner 

 face of the ramus is gently concave. The anterior origin of the coronoid 

 process is opposite the posterior border of the second molar. 



In the mandible the condyle projects as far backwards as the angle, 

 and is hence quite a distance posterior to the coronoid process. The 

 latter is small, and is a little higher than the condyle. The angle has 

 an acuminate apex, which is turned out. The posterior extremity of the 

 incisive alveolus forms a prominent tuberosity, bounding a fossa of the 

 ascending ramus on its external side. The inferior outline of the mandible 

 follows the curve of the incisor tooth anteriorly to the middle of its length, 

 when it reaches the line of the inferior border of the masseteric fossa. 

 Here it commences another convexity, which is most prominent directly 

 below the incisive tuberosity, and ascends again to the angle. 



The triturating surface of the molars is not oblique, as in E. planifrons, 

 but is nearly horizontal. The enamel of the incisor is smooth, and has 

 a well-marked bounding angle at the inner edge, and another within the 

 external edge. 



Measurements. 



H. 



Length of inferior molar series 0082 



Width of anterior face of inferior incisor 0028 



Depth of ramus at M. ii 0090 



Width of ramns below at M. ii 0052 



Though this species is larger than any other species excepting the JE. 

 planifrons, its interorbital width is the least. Its peculiar frontal groove is 

 only approached by some specimens of the Pleurolicus sulcifrons. I have 

 only two crania which undoubtedly belong to the jB. crassiramis, while a 

 third very probably may be referred to it. Both the former have mandibles 

 attached. 



John Day River, Oregon. 

 65 



