224 BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



Order Condylarthra — Continued. 



Family Periptychidae: Cliaracterized by persistently plantigrade feet and by 

 teeth markedly bunodont, the premolars not becoming molariform (as in 

 other families) but evolving independently into large swollen crushing 

 teeth, the molars relatively small, with the primary cusps conical and 

 crowded together, developing a peculiar type of polybuny especially 

 in the upper teeth by the development of new cuspules largely internal to 

 the primary cusps. 



Subfamily Anisonchinae: Small and slender forms with the basic dental 

 characters of this family, but the teeth relatively simple and general 

 structure apparently closely similar to the Hyopsodontidae. Lower 

 to Middle Paleocene. North America. 

 Subfamily Periptychinae: Larger subgraviportal forms developing heavy 

 limbs and somewhat amblypodlike feet, with complex, polybunous 

 molars. Lower to Upper Paleocene. North America. 

 Family Meniscotheriidae: Hyracoidlike animals of middle size with lopho- 

 or buno-selenodont teeth, serial carpus and tarsus, and narrow, hooflike 

 unguals. Their early history is unknown and their relationships doubtful. 

 They may not be very close to the other condylarths. Their dental evolu- 

 tion seems to have been in a direction distinct from any other primitive 

 ungulates, and almost opposite that of the periptychids, but could have 

 started from a common basis in the Paleocene. 



Subfamily Meniscotheriinae: Typical, more lophiodont forms. Upper- 

 most Paleocene and lower Eocene. North America. 

 Subfamily Pleuraspidotheriinae: More bunodont forms, of still more 

 dubious position. Upper Paleocene. Europe. 



In the present fauna the Hyopsodontidae are very abundant and 

 varied. Phenacodonts are present but are not abundant, being espe- 

 cially rare in the quarry facies. Anisonchines are not uncommon 

 but are limited in variety, only two genera and species being recog- 

 nized, and are much less common or varied than in the Puerco and 

 Torrejon. The Periptychinae, so common in the San Juan Basin 

 faunas, appear to be wholly lacking. Meniscotheres are absent, as 

 would be expected since this group is Imown only from younger strata. 



Family HYOPSODONTIDAE Lydekker, 1889 



The small Paleocene animals now believed to be condylarths allied 

 to Hyopsodus have had a confusing and complex history, which is 

 here to be sketched only in its more essential points. Cope's genus 

 Mioclaenus was at first referred by him to the Condylarthra, but he 

 later removed it to the Creodonta on the basis of the skeletal characters 

 of "Mioclaenus" ferox. Pie referred many species to the genus, mak- 

 ing it a sort of dumping ground for unspecialized dentitions of more 

 or less bunodont, tubercular-sectorial type. Schlosser, in 1886, sug- 

 gested that Mioclaenus might really be a condylarth (as Cope origi- 

 nally supposed). Scott (1892) separated out a number of Cope's 

 species and placed them in distinct genera. "M." ferox was then 

 made the basis for the genus Claenodon, a true creodont. Scott then 

 considered that true Mioclaenus, really allied to the type M. turgidus, 



