NEW PALEOCENE MAMMALS SIMPSON 239 



drafts of part of his brief account of the phenacodonts. None is com- 

 plete, it is not certain which is most recent, they are not consistent 

 with each other, and they have notations for further study never made 

 or, at least, recorded. It is thus improper to publish these notes as 

 they stand and impossible to edit them in such a way as to be sure of 

 representing Dr. Gidley's views correctly. I have therefore studied 

 the group de novo, but have incorporated as many of Gidley's names 

 and diagnoses as possible. 



Genus TETRACLAENODON Scott 



TETRACLAENODON SYMBOUCUS Gidley. new species, ex ms. 



Type. — U.S.N.M. no. 6169, part of right lower jaw with Mi and 

 alveoli of P3.4 and M2. Collected by A. C, Silberling. 



Paratype. — (Added by Simpson.) U.S.N.M. no, 6168, jaw fragment 

 with right M1.2 and an isolated left P4. Collected by A. C, Silberling. 



Diagnosis.— Gidley: "This species is smaller than E. [Tetraclaenodon] 

 puercensis, being about intermediate in size between that species and 

 E. minor [Tetraclaenodon plicij'erus]. The lower molars are propor- 

 tionately narrower transversely than those of the former species and 

 the lower jaw is much shallower. This last character may be due in 

 part, however, to a less mature condition of the specimen which rep- 

 resents a young individual with the first true molar just coming into 

 use. The striking similarity in detail of the lower molars with those 

 of E. [T.] puercensis is a notable feature of the species and separates 

 it clearly from E. minor [T. pliciferus]. The more notable points of 

 similarity are the slight roughening and wrinlding of the enamel sur- 

 face and a tendency of the teeth to break up into small cuspules," *^ 



Simpson: Intermediate between Tetraclaenodon plicijerus and T. 

 puercensis in size but nearer the former both in size and structure. 

 The only constant difference from T. plicijerus is greater size, inade- 

 quate for specific differentiation were it not correlated with wide geo- 

 graphic separation, Crenulations perhaps slightly more pronounced 

 and paraconid weaker than in T. plicijerus, but these are highly vari- 

 able characters of doubtful taxonomic value. Mi, 3 specimens, length 

 7.5-7.9 mm, width 6.3-6.4 mm. M2, 2 specimens, length 7.8-8.2 mm, 

 width 7 mm. Ratio trigonid width : talonid width M2 1.01-1.06. 



7TETRACLAENODON SUPERIOR, " new species 



Type. — U.S.N.M. no. 11913, part of left lower jaw with talonid 

 of Ml, unworn M2, and M3 in capsule. Collected by A. C. Silberling, 



Horizon and locality. — LocaUty 11 or 13, about 3,000 feet above 

 the Gidley Quarry, Fort Union, Middle or perhaps Upper Paleocene 

 horizon, Crazy Mountain Field, Mont. 



" This appears to be a good distinction from figures of T. pliciferus, but actual specimens of the latter do 

 not differ markedly from T. symbolicus in this respect.— Q. O. S. 

 " Superior, higher, in reference to its stratigraphic position. 



