NO. I LOWER EOCENE MAMMALIAN FAUNAS — GAZIN 7I 



is an M^ from another individual. The difference between the two 

 M^'s is then a matter of wear and of individual variation. The extent 

 of the difference between them with respect to the posterior spur from 

 the protocone was observed between two sides of the same skull as 

 mentioned above. 



The pair of jaws from Bitter Creek (U.S.N.M. No. 22746) in- 

 cludes the three molars. M3, as in the tooth so identified by Cope 

 (pi. 49, fig. 6) has the posterior crest parallel to the anterior. This 

 condition is quite like that in the lower jaw regarded as associated 

 with the type of C. radians (Cope's pi. 46, fig. 2). Lower jaws with 

 a skull (U.S.N.M. No. 21026) from the Gray Bull horizon at the 

 base of the escarpment west of Elk Mountain in the Fossil Basin 

 also show (see pi. 12, fig. i) this type of M3. None of the Knight 

 lower jaw material so far observed exhibits the so highly divergent 

 or V-shaped posterior crest characterizing the genotype C. eocaenus, 

 and that is comparatively common in Bighorn Basin specimens. The 

 C. eocaenus condition exhibited by the Bighorn Basin specimens 

 would appear to be primitive, and more like the Paleocene pantodonts, 

 as pointed out to me by Dr. Elwyn Simons, although the form repre- 

 senting this condition in the Gray Bull fauna of the Bighorn Basin 

 cannot, of course, be ancestral to that at Bitter Creek. Dr. Simons 

 has undertaken a study of Coryphodon as a sequel to his study of 

 Paleocene pantodonts, and his much-to-be desired revision of the 

 numerous species of Coryphodon and his conclusions on their rela- 

 tionships is eagerly awaited. 



DINOCERATA 



UINTATHERIIDAE 



Cf. BATHYOPSIS FISSIDENS Cope 



Further excavation in 1953 at the locality where jaws described as 

 probably representing Bathyopsis fissidens (U.S.N.M. No. 19990) 

 were found has yielded considerably more skeletal material. The bone 

 is rather badly shattered but careful preparation has saved about 

 nine presacral vertebrae, including the atlas and axis, together with 

 the sacrum and several rib portions. Representing the forelimbs is the 

 distal part of a humerus, both radii, the greater part of both ulnae, 

 and three carpals. The hindlimbs are represented by the head and 

 condyle of a femur, patellae, a nearly complete tibia, almost all of the 

 right tarsus, and the third metatarsal. 



The limb material for the most part is rather flattened by crushing, 



