538 PUERCO FAUNA 



cusps of the true molars are alternate, and the internal intermediate of the 

 last molar is near the lifth lobe or heel of the same. 



The symphysis of the mandible is not coossified, in contrast to the con- 

 dition in Tomitherium. There are three mental foramina, one below the 

 second and one below the anterior part of the fourth premolars. 



Measttrements. 



M. 



Length of superior dental series 0262 



Length of superior incisors 0060 



Length of superior true molars 0100 



Diameters M. jj ^ anteroposterior 0036 



( transverse 0050 



Length of inferior incisors, oblique on bases 0030 



Length of inferior true molars 0110 



Diameter of root of inferior canine 0020 



Diameters Pm. iv | •■'°«"<'P««^rior 0027 



< transverse 0024 



Diameters M. ;; ^ anteroposterior 0039 



( transverse 0030 



Diameters M.iii^ ="'*"«?"*"•■"'"• '^^^ 



( t ransverse 0030 



Eleven mandibular i-ami were procured from the Big Horn Basin, and 

 a smaller number from the Wind River. Among the former, a few specimens 

 are intermediate between this species and the last in dimensions, the inferior 

 true molars measuring M. .0120 and .0125 in length. 



Hygpsodus acolytus Cope. 



Proceed. Araer. Philos. Soc, 1882, p. 462. Paleontological Bulletin No. 35 (Nov. 11, 1882). 



Plate XXIlId, figs. 5-6. 



This, the least species of the genus, is also the oldest, being derived 

 from the Puerco horizon. Parts of the two individuals furnish the charac- 

 ters of the inferior and superior true molars, and the fourth superior pre- 

 molars. The species differ from those hitherto described in other charactei^s 

 than the minute size. One of these is the absence of posterior interior cusp, 

 the heels of the first and second true inferior molars being l)ounded b}- a 

 ridge only at this point, as in most of the species of Pclycodus. The last 

 inferior molar is not smaller than the second, nor longer. The anterior 

 cusps of all the molars are robust, so that on the first and second true 

 molars they are separated by a shallow notch only. There is a rudiment 

 of the anterior inner cusp on the first true molar, but more o\\ tlie .second 



