FORT UXIOX OF CRAZY MOUNTAIN FIELD, MONT, 195 



conids reduced and in nearly the same position as in Thryptacodon but 

 more distinct, higher on crown, trigonids less basined, and with fewer 

 accessory cuspules. Only one distinct inner talonid cusp (entoconid), 

 as opposed to two in Thryptacodon. 



Discussion. — This genus could well be ancestral to Thryptacodon 

 and in any case is evidently allied to it. The adaptive characters are 

 somewhat intermediate betv»'een the more primitive types, such as 

 Oxyclaenus, and the more complex type seen in Thryptacodon, involv- 

 ing some flattening of the molar crowns and proliferation of cuspules. 

 In these characters Thryptacodon and to a less extent Prothryptacodon 

 parallel or converge toward the Claenodon-Anacodon hne. The latter 

 group, how^ever, is much earlier and more highly specialized in this 

 rather bearlike direction. Prothryptacodon is contemporaneous with 

 Claenodon in the Middle Paleocene, and Claenodon is already more 

 specialized than Thryptacodon in this direction. Thryptacodon 

 appears in the Upper Paleocene and survives into the lower Eocene, 

 where Anacodon appears as a highly aberrant survivor of the Claenodon 

 group. 



The canine is slender, laniary, compressed, with the root con- 

 siderably larger than the crown and meeting the latter at an angle of 

 about 135°. The root is implanted almost horizontally and extended 

 at least to the anterior end of Po. Pj, from its alveolus, had a single 

 root and was well spaced, slightly nearer to the canine than to P2. 

 Pa and P3 were 2-rooted, and P2 is preceded and followed by a short 

 diastema. P4 has a very slight internal swelUng, high on the crown, 

 that may indicate an incipient metaconid. In one specimen M2 has a 

 faint external trigonid cingulum, and in another this is more definite. 

 There are two mental foramina, one beneath Pi and one beneath P3 

 or the anterior end of P4. The other characters of genus and species 

 are adequately given in the diagnosis and figures. 



PROTHRYPTACODON FURENS SimpsoB 



FiGUBE 45 



Prothryptacodon furens Simpson, 1935d, p. 234. 



Type. — U.S.N.M. no. 9260, right lower jaw with P4-M3 and 

 alveoli. Collected by A. C. SilberUng. 



Horizon and locality. — Gidley Quarry (referred specimen from 

 Silberling QuarrjO, Fort Union, Middle Paleocene horizon, Crazy 

 Mountain Field, Mont. 



Diagnosis. — Sole known species of genus. Measurements in 

 table 40. 



Remarks. — Only two specimens are as yet known, both partial 

 lower jaws. U.S.N.M. no. 9262 is from the Silberling Quarry. 



