172 THE WASATCn AND DUIDGER FAUN^. 



The posterior is closed by an elevated convex margin. Tiie apices of the 

 lobes are obtuse where not distinctly worn. The last (second) true molar 

 is much shorter and a little wider than the first, and has the same character 

 of surface. There are two large tubercles on the inner side and four small 

 ones on the external side. The posterior end of the crown is narrower than 

 the anterior. The anterior base of the coronoid i)rocess is opposite the 

 posterior e.xtremity of the first true molar tooth. The jaw, with its denti- 

 tion, in its present condition, has a curious resemblance to that of a tuber- 

 cular-toothed Mastodon, witli the order of size of the molars reversed. 



Measurements. 



u. 



Length of base of true inol.irs 0166 



Length of base of fourth premolar OlO(j 



Vertical diameter of root of incisor 0070 



Diameters M. i J ""'•^■""P"*'^'"'"'" ^^^' 



( transverse OO.'.O 



Diameters M. ii ^i-'t'T'.posterior 0060 



( transverse OOIM 



Depth of ramns at front of P-ni. iv 0120 



Depth of ramus at front of M. i 0190 



Depth of ramns at posterior eilge of .M. ii Ol.'O 



Width of ramus below P-m. iv 0070 



"Width of inferior face of ramns below M. ii 0110 



Found by my assistant, D. Baldwin, in the Puerco Formation of North- 

 western New Mexico. 



PTILODUS Cope. 



American Naturalist, ISBl, November, p. 921 (October 28). 



Dental formula of infeT-ior series; I. 1 ; C 0; Pin. 'J; M. 2. Incisor 

 occupying- a deep alveolus and probably growing from a persistent pulp. 

 It forms an arc of a circle, with an anterior enamel band. First (third) 

 premolar rudimental. Second (fourth) premolar disproportionately large, 

 with compressed crown with a convex cutting edge, and lateral ridges di- 

 rected upwards and posteriorly. Molars small; the first longer tiian wide, 

 its crown divided by a deep longitudinal median groove into two lateral 

 ridges, which are divided into lobes by transverse fissures. Tlio masseteric 

 fossa is well marked. The intcnial pterygoid fossa is very deep and termi- 

 nates in the foramen dentale, and is bounded below by a horizontal iuHection 

 of the inferior border of the mandiltiil.ii- minus. 



