FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 



247 



Horizon and locality. — Type from Silberling Quarry, paratype from 

 Loc. 25, about 250 feet lower stratigrapliically, Fort Union, Middle 

 Paleocene horizon, Montana. 



Figure 70. — Tttradaenodon symbolicus Qidley, 

 U.S.N.M. no. 6169, right lower jaw (with Mj): a, 

 Crown view; b, internal view. One and one-half 

 times natural size. 



Figure ll.—Teiraciaenodon syinbolicus Gidley; 

 a, U.S.N.M. no. 6168, right Mi_2, crown view; 

 a', same internal view; 6, Princeton Univ. no. 

 13757, right Ms-3, crown view. One and one- 

 half times natural size. 



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

 G. G. S.j puercensis, being about intermediate in size between that 

 species and E. minor [= Tetraclaenodon pliciferus, G. G. S. ]. The 

 lower molars are proportionately 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 represents 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., G. G. S.l puercensis is a notable 

 feature of the species and separates it clearly from E. minor [T, 

 pliciferus, G. G. S.]. The more notable points of similarity are the 

 slight roughening and wrinkling of the enamel surface and a tendency 

 of the lophs of the teeth to break up into small cuspules." ^ 



Simpson: Intermediate between T. pliciferus and T. puercensis in 

 size, but nearer the former both in size and in structure. The only 

 constant difference from T. pliciferus is the greater size, inadequate 

 for specific differentiation were it not constantly correlated with the 



* And within the range of T. pliciferus in this proportion.— O. O. S. 



• A specimen of T. pliciferus of comparable age has a deeper jaw, despite its smaller teeth but a referred 

 specimen of T. symbolicus also has a deep jaw. This is probably a highly variable character, and also depends 

 on crushing to a considerable degree.— Q. G. S. 



« From figures of the Torrejon specimens this would seem a striking and good distinction, but the speci- 

 mens themselves show that T. pliciferus also has wrinkled enamel and a tendency for lophs to break up into 

 cuspules. These may be functions of size, to a limited extent, and slightly less pronounced in T. pliciferus 

 than in T. puercensis. T. symbolicus is about intermediate between the two in these characters, as in size. 



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