OF THE WHITE RIVER OLIGOCENE. 59 



flange and the dependent mandibular processes. The outward and 

 backward slope of the cheek flange (Fig. i ^) is undoubtedly ac- 

 centuated by crushing, but its width has not been increased thereby. 

 Apart from its greater size, the part remaining is not essentially unlike 

 that of the small skull in the American Museum collection (Hat 

 Creek specimen), which, in turn, except for the reduced m^, can not 

 be distinguished from our No. 12709 shown in Fig. i B and regarded 

 as typical A. mortoni. 



The type of A. coarctatum lacks the inferior mandibular border 

 anterior to the "first" (fourth) premolar, consequently the shape of 

 the dependent processes is unknown. Both processes are lost by 

 decay in No. 12624 (Fig. 2), but were evidently present. Fortu- 

 nately, they are well preserved in the Hat Creek specimen (Am. 

 Mus., No. 1481), where they are seen to be of the A. mortoni type, 

 made familiar by Peterson's drawing.^ 



Turning now to A. mortoni, the type specimen, a fragment of the 

 maxillary with p^ and p* in place, figured by Leidy on Plate IX., 

 Fig. 3, " Ancient Fauna of Nebraska," is manifestly inadequate from 

 the modern point of view, but we must not forget that Leidy was just 

 as fully entitled to find his own original type inadequate as any sub- 

 sequent writer and, therefore, to redefine it in terms of other speci- 

 mens. The young individual with milk and permanent dentition 

 which he figures on Plates VHI. and IX. of the Ancient Fauna is, 

 therefore, an " heutotype," as this term is defined by Schuchert and 

 Buckman.'^ On this specimen, I submit, the species Archceothcrimn 

 mortoni is adequately founded. It is an individual with richly tuber- 

 culated third upper molar, with three cusps in the front row and a 

 large number of small tubercles in the posterior row among which the 

 metacone, metaconule, hypocone, posterior cingulum and an additional 

 cusp anterior to the metacone and metaconule may be made out, 

 although by no means as distinctly as in Fig. 3 E and F. There may 

 be departures from this fully tuberculated type of m^ in the develop- 

 ment of the hypocone which may be barely distinguishable from the 

 posterior cingulum (Fig. 3 Z)) or large and fully formed (Fig. 3 



5 Loc. cit, p. 48, Fig. 4. 



^ Science, N. S., Vol. 21, No. 545, p. 900, 1905. 



