FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 



249 



specimens were derived. Nevertheless the material is well unified, 

 and data on it can be more adequately summed up in statistical form 

 than otherwise. (Table 57.) 



The dimensions of the two specimens not from Loc. 25 are given 

 in table 58. 



Table 58. — Individual measurements {in mm) oj lower molars of Tetraclaenodon 



symbolicus 



These are to some extent marginal, as might be expected. The 

 type, from the Silberling Quarry, has the largest Mi recorded, but a 

 specimen from Loc. 25 approaches this within 0.1 mm. No. 9925, 

 from Loc. 3, has the widest Mi and IM3 recorded, but these two dimen- 

 sions are approached within 0.2 and 0.1 mm, respectively, by Loc. 25 

 specimens. The variation is low for the whole series in any event, 

 and there is no reason to believe it heterogeneous as to race. 



The close approach of this species to T. pliciferus is shown by the 

 dimensions of Mi of the type of the latter, length 7.5, width 6, within 

 the range of T. symbolicus but slightly below the mean. The most 

 readily measurable of the types of T. "minor" == T. pliciferus, Amer. 

 Mus. no. 3897, has the following dimensions: Length Mj, 6.8; width 

 Ml, 5.6; length M2, 7.0; width Mo, 6.2. 



This is somewhat more representative of the smaller Torre] on 

 species than is the type of T. plicijerus, which is a large variant. 

 The lengths are below and the widths at the observed lower limits 

 for T. symbolicus, and the differences are significant. 



Princeton no. 13757, from Loc. 9, one of the rare No. 1 Fort Union 

 specimens, includes M^~^ evidently of Tetraclaenodon and closely 

 comparable to T. symbolicus, although the variability of this species, 

 lack of adequate material of the upper dentition, and some differ- 

 ences from other specimens, perhaps individual and perhaps of minor 

 taxonomic value, make the reference uncertain. 



TETRACLAENODON cf. PUERCENSIS (Cope, 1881) 



A few fragmentary specimens demonstrate the presence of a larger 

 species of Tetraclaenodon. These include a left upper M^ from the 

 Gidley Quarry (U.S.N.M. no. 9620), associated left dm^ and M^ 

 from Loc. 6 (American Museum), associated left M^ and part of 



