182 FIELD COLUMBIAN MusSEUM—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. 
Asin 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. Atthe 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, witha 
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 fossz 
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. 
