Vertebrate fauna of the blAnco beds. 71 



is, on the contrary, robust. There is a large foramen mentale, which is 

 below the posterior border of the fourth premolar. The inferior face of 

 the symphyseal region presents a deep groove on the middle line distally 

 between the roots of the median incisors. 



The median four incisors stand on a nearly transverse line, while the 

 external ones are sublateral. In their present state of wear the masticat- 

 ing surfaces of the middle pair form very wide ovals, with the longer 

 diameters converging posteriorly. The surfaces of the second incisors 

 are narrower and are acuminate exteriorly, while those of the third are 

 still narrower and more acuminate externally and posteriorly. The ca- 

 nines are very robust, and point forward, upward and outward. There 

 is an enamel ridge on the outside of the oblique anterior face, and there 

 is a less prominent ridge on the apical part of the middle line posteriorly. 

 Between these crests the external face is much more convex than the in- 

 ternal one, and the latter exhibits a shallow groove just behind the ante- 

 rointerual keel. 



The fourth premolars have about half the linear dimensions of the ca- 

 nines, and the crowns are compressed and present cutting edges anteriorly 

 and posteriorly near the apex. The internal walls of the other premolars 

 and molars are less deeply grooved than the external walls, but they are 

 not nearly so flat as in the Holomeniscus hesternus. The internal walls of 

 the premolars present a gentle concavity, with an internal incurvature at 

 the anterior apex. The external walls present two concavities, a long 

 anterior and a short posterior. The posterior end of the crown is nar- 

 rowed in p. m. ^, and truncate in p. m. 77 The true molars increase rap- 

 idly in size posteriorly. The first differs from the second and third in 

 lacking vertical folds or ridges at the anterior and posterior extremities 

 of the first and second columns, which give the anterior and posterior ex- 

 tremities of the latter respectively an incurvature. The same rib is pres- 

 ent on the internal side of the posterior extremity of the third lobe of 

 the last true molar. There are no cingula on any of the teeth. The en- 

 amel is everywhere longitudinally roughened, except where polished by 

 use. 



Measurements. 



Mm. Mm. 



Pli. Hoi. 



spatula, hesternus. 



Length of ramus from posterior extremity of M. ill. to incisive 



alveolar border 401 302 



Length of symphysis 150 90 



Width of mandible at I. iii. inclusive 95 57 



Width of mandible at P. m. iv 65 



Length from alveolar border to canine (inclusive) 60 55 



Length from canine to P. m. Iv 23 



Length from canine to P. m. ii 145 



Length from canine to P. m. i 168 85 



