NO. 8 UPPER EOCENE ARTIODACTYLA — GAZIN 4I 



uintensis as not distinct from A. robustus, but since the two are not 

 from the same beds and there may be some doubt as to their age 

 equivalence, A, uintensis is tentatively retained. 



MEASUREMENTS IN MILLIMETERS OF DENTITION IN A REFERRED SPECIMEN ^'^ 



OF Achaenodon uintensis, a.m. no. 2047 



Length of upper cheek tooth series, anterior margin of alveolus for 



C to posterior margin of M* 210.0a 



Length of upper cheek tooth series, anterior margin of alveolus for 



P^ to posterior margin of M^ i7S.oa 



Upper molar series, M*-M^, inclusive 83.5 



C, anteroposterior diameter (at alveolus) : greatest transverse diame- 

 ter 35.5 : 35-5 



P^ anteroposterior diameter : greatest transverse diameter 32.0 : 23.5 



P*, anteroposterior diameter : greatest transverse diameter 27.5 : 35.5 



M\ anteroposterior diameter : transverse diameter anteriorly 25.0 : 31.0 



M^ anteroposterior diameter : transverse diameter anteriorly 27.0 : 37.0 



M", anteroposterior diameter : transverse diameter anteriorly 32.5 : 36.0 



a, Approximate. 



Genus PARAHYUS Marsh, 1876 



Type. — Parahyus vagus Marsh, 1876. 



Discussion. — The close resemblance of Parahyus to Achaenodon 

 was observed by Osborn (1895), who did not regard the genera as 

 distinct. Osborn noted, however, that Cope believed them to be 

 different, primarily on the assumption that Achaenodon had one more 

 premolar. Although this distinction does not exist, Parahyus has been 

 rather generally treated as a separate genus, possibly in part as a result 

 of the doubt regarding its geologic age. Parahyus, like Achaenodon, 

 is characterized by three large, single-cusped premolars, with P4 much 

 the largest, and simple bunodont molars. However, the one valid 

 species, in addition to being much smaller than Achaenodon, has 

 molars relatively much longer in relation to the depth of the jaw and 

 to the length of the premolar series than in Achaenodon, in which 

 respect it is about intermediate between Helohyus and Achaenodon. 

 Like Achaenodon it differs from Helohyus essentially in the loss of a 

 premolar (if the latter had four, as suggested by Sinclair in 1914) ; 

 in the more-inflated appearance of the cusps ; and in the reduction or 

 suppression of the paraconid on the lower molars and of the hypo- 

 conulid on Mi and M2. 



^^ Teeth not preserved in type specimen. 



