182 Field Columbian Museum — Geology, Vol. i. 



The specimen consists of a single mandible from which the angle, 

 condyle, part of the coronoid process and the tip of the incisor have 

 been lost. The remainder is in good preservation and shows a per- 

 fect molar dentition. The teeth are deeply set in the alveolus and 

 their well-worn crowns indicate an animal fully adult. The molars 

 are ranged in a line parallel to the plane of the symphysis, but the 

 axes of the teeth themselves are inclined well inward at the crowns. 

 As in Mylagaulus, the angle of the mandible is within the plane of the 

 incisive alveolus, but the condyle would fall somewhat without it. 

 The coronoid process is strong at the base and is directed outward, 

 leaving a broad fossa between its mesial surface and the posterior 

 molars. At the hinder margin of this fossa the dental foramen opens. 

 Almost continuous with the anterior margin of the coronoid process, 

 arising just below the posterior third of the premolar alveolus and 

 extending downward toward the angle, is a strong masseteric ridge. 

 The symphysis extends far back beneath the premolar alveolus where 

 its termination forms a prominent angle in the inferior outline of the 

 mandible. The ramus is concave on the mesial surface throughout, 

 and posteriorly bears evidence of a deep fossa. The incisor is cov- 

 ered anteriorly with a thin orange-colored enamel. At the alveolus, 

 where it is broken, the section is roughly sub-triangular. The ante- 

 rior surface meets the median one in a sharp angle ; with the lateral 

 surface it forms a rounded one ; while posteriorly the faces converge 

 to form a single rounded surface. The premolar, as before men- 

 tioned, has its crown much elongated antero-posteriorly and the 

 enamel slightly inflected on the lateral margin. A series of three 

 enamel fossettes are arranged in the median line of the crown, with a 

 trace of a fourth lying lateral to them. The anterior surface is 

 comparatively narrow, the crown reaching its greatest width oppo- 

 site the third fossette, while opposite the middle one occurs the exter- 

 nal enamel inflection. The second molar is a small tooth, com- 

 pressed antero-posteriorly, and like the third, entirely devoid of fossae 

 or enamel inflections. In both, the enamel is absent from the mesial 

 surface and in the first it is noticeably thinner. All are encased in 

 thick sheaths of cement. The last molar is grooved on the mesial 

 surface throughout its length, indicating the not very remote coales- 

 cing of roots. The other molars I have not examined below the alve- 

 olus. A possible trace of a fourth alveolus remains, but the space 

 between the third molar and the dental foramen is so reduced that a 

 fourth tooth could not have developed in this individual. 



