548 



TITANOTHERES OF ANClfiNT WYOMIMG, DAKOTA, AND NEBRASKA 



Referred, skull, Megacerops acer, University of Wyo- 

 ming Museum. — ^A very fine skull (figs. 452, 453) in 

 the University of Wyoming, collected by Mr. W. H. 



Figure 452. — Skull of Megacerops acer 



Dniv. Wyoming Mus. 2. Side (Ai) and top (Az) views. One-sixth natural size. This sliiill combines the 

 characters of several supposed species of Megacerops. In the form and length of the horns it approaches 

 the type of M. acer; in the character of the nasals it resembles the type of Symborodon attirostris; in the 

 general form of the skull top it resembles especially the supposed female of M. biicco (Nat. Mus. 4705); 

 and in the dimensions of the grinding teeth it agrees with the lectotype of M. bucco (Am. Mus. 6345a). 



Eeed in the upper Titanoiherium zone near Alcova, 

 Natrona County, Wyo., has somewhat smaller horns 

 than the type. Its nasals recall those of the type of 

 S. altirostris. The premolars, as in other members of 



the genus, have the internal cingula nearly obsolete 

 and the tetartocones subequal to the deuterocones; 

 the width of the molars exceeds the length. The zygo- 

 matic index (84) is high. In addition 

 to the measurements of this skull 

 given above (p. 542), we record also 

 the following: 



MilUmeters 



Diastema behind canine 20 



PS ap. by tr 34X45 



M2, ap. by tr 73X84 



M3, ap. by tr 78X83 



Molar inde.x 29 



Megacerops copei (Osborn) 



{Symborodon copei Osborn, 1908) 



Plates CXLIII-CXLV; text figures 24, 203, 

 390, 394, 399, 450, 454, 640 



[For original description and type references see p. 235] 



Geologic horizon — Middle Titano- 

 iherium zone. South Dakota. 



Specific and generic characters. — 

 JZiO.^ p4 Incisors (type) persistent 

 but greatly reduced; canines very 

 small, reduced, c? 28 millimeters; 

 premolars with cingula reduced or 

 absent; tetartocones connected with 

 deuterocones by a longitudinal ridge. 

 Skull: Nasals thin, short and broad 

 in proportion, 80 by 125 millimeters; 

 horns S 300, no connecting crest, 

 transverse oval near summit; buccal 

 processes of zygomata c? stout and 

 convex; malar in front of buccal 

 process very deep, beneath postorbital 

 process stout, convex; occipital pillars 

 medium, not greatly expanded at the 

 summits. Size small, premaxillaries 

 to condyles 620 millimeters. 



Materials. — This species is known 

 only from the type skull (Nat. Mus. 

 4711, skuU V), which is finely illus- 

 trated in Plates CXLIV, CXLV. It 

 is from the middle Titanotherium zone, 

 probably from the upper levels or 

 even lower, and impresses one with 

 the excessive thinness of the nasals, 

 which in these animals are very broad 

 posteriorly (120 mm.), while not of 

 very great free length. The animal 

 is in the eighth stage of growth 

 and has thus attained its fully adult 

 characters. The small size of the canines (28 mm.) 

 might lead us to regard it as a female, but all the 

 specimens belonging to this genus are characterized 

 by small canines, and the great length of the horns 



