OF THE WHITE RIVER OLIGOCENE. 63 



te'r^n in m^, may be regarded as progressive, but among contemporary- 

 individuals in the series the increments of change appear to fluctuate 

 in an irregular way, certain cusps in less advanced teeth being very 

 large, while in more advanced teeth they may be quite small (compare 

 m^, Fig. 3 C, E) , or small in some and large in others (m^, Fig. 3 

 E, F). Small bodily size is not confined to individuals with less 

 complex m-^ or those with the anterior lower premolars unspaced, and 

 these are connected with the more richly cuspidated and fully spaced 

 types by such a transitional form as No. 1483, Am. ^lus., where m^ 

 resembles Fig. 3 D, and there are very short spaces between the ante- 

 rior lower premolars. So far as the assumed primitiveness of A. 

 coarctatum is concerned, every one of its characters which might be 

 regarded as primitive is possessed in some degree by specimens which 

 differ from it in other respects, as I have tried to show, and we are 

 faced by two alternatives, either the naming of every variant, which 

 results in making practically every specimen a separate species, for 

 almost every one of them shows a new grouping of characters which 

 appear somewhere else in a different association, or the referring of 

 the lot to one species for which the name A. morfoni has priority and 

 which seems, as Dr. Matthew has suggested to me in another con- 

 nection, to be made up of several interbreeding strains, diagrammati- 

 cally a number of anastomosing lines, which differ by various small 

 unit characters or combinations thereof, transmitted to the individual 

 from the various pure lines which enter into its ancestry. Reference 

 to the accompanying table of measurements will show a considerable 

 range in size, but I am not able to correlate this, as already indicated, 

 with the structural variations noted above. 



The situation with regard to these small entelodonts suggests that 

 certain of the structural differences which have been used for the 

 separation of some of the larger forms would be found to intergrade 

 if we had larger series of contemporary specimens, which, unfortu- 

 nately, do not yet exist in museum collections. If the conclusions 

 reached above are well founded, it may be considered certain that 

 A. mortoni ranges down into the Titanotherium beds,^^ but neither it 



1^ Peterson reports a number of skulls, portions of skulls and teeth in 

 the Carnegie Museum, collected by himself and others from the Titanotherium 

 beds of Nebraska and South Dakota and agreeing with A. mortoni as figured 

 by Leidy. Peterson, loc. cit., p. 47. 



