248 



BULLETIlSr 169, UNITED STATES NATIONAL MUSEUM 



widely different geographic distribution, as far as kjiown. Crenula- 

 tions possibly slightly more developed and paraconid weaker on type 

 and paratype of T. symbolicus, but these are variable characters and 

 other specimens suggest that they are not of specific value. 



Discussion. — This species seems to be variable, and it is difficult to 

 separate it from T. pliciferus, with which it must be closely related. 

 Its smallest variants, indeed, could not be separated from T. pliciferus 

 were they found together, but the homogeneous sample from Loc. 

 25 averages larger than T. pliciferus. Since all these individuals are 

 from one horizon and locality they evidently represent either one 

 herd or an actually interbreeding stock, the character of which is thus 

 slightly different from the Torrejon species and may be given taxo- 

 nomic distinction. The size dift'erence is statistically significant. I 

 therefore accept Dr. Gidley's species, but consider it as much closer 

 to T. pliciferus than he believed. 



It happens that the type and to less degree the paratype have the 

 enamel unusually crenulated and the paraconids small, characters 

 slightly closer to T. puercensis than to T. pliciferus, although those 

 species intergrade in this respect. The other specimens from Loc. 

 25, however, have the enamel somewhat smoother and the paraconids 

 more distinct, almost exactly as in T. pliciferus.'^ 



The more recently discovered specimens include one with dm4, 

 representatives of all the lower molars and of P2 and P4, and also 

 M^~^. These are all morphologically within the range of T. pliciferus. 

 They might be grouped into three subdivisions, large, medium, and 

 small, but I think the grouping would be subjective and that the 

 variation is individual and approximately normal. 



Table 57. — Numerical data on lower molars of Tetraclacnodon sjmbolicus 



The available material (including that in the American Museum) 

 provides only six well-preserved examples of each of the three lower 

 molars, and it is not entirely homogeneous since the type and one 

 other specimen (as given below) are not from Loc. 25, whence all other 



» One of the most extreme specimens in this respect, U.S.N.M. no. 6167, was referred to T. symbolicus by 

 Qiflley, in his notes, so that his conception of the species was the same as mine despite the differences in the 

 diagnosis. 



