45 



Measurements. 



Aceratherium exiguum compared with A. mite (pumilum). 



A. exiguum. A. mite. 



MM. MM. 



Length of symphysis, approx 58 40 



Depth in front 18 18 



Depth behind 26 21 



Distance apart of premolars 2 27 32 



Space occupied by premolars 2 and 3 30 23 



Autero-posterior diameter of premolar 2 1 2 • 5 9 



Breadth of jaw transversely across alveoli for canines . . 42 33 



Height of alveolus for canine 12 7 



Width " " " " 16 10-5 



Depth of ramus below posterior end of diastema 38 32 



Depth " " " premolar 3 46 39 



Megacekops angustigenis (Cope). 



Menodus angustigenis, Cope, 1885. Geol. and Nat. Hist. Survey of Canada, vol. I, new- 

 series, part C, appendix I, p. 81. 



Haplacodon angustigenis, Cope, 1889. The Vertebrata of the Swift-current river, II, 

 American Naturalist, vol. XXIII, p. 153. 



Menodus angustigenis, Cope, 1891. The species from the Oligoceno or Lower Miocene 

 beds of the Cypress hills ; Geol. Survey of Canada, Contr. to Can. PaUvont., vol. Ill, 

 (quarto), pt. I, p. 13, pi. V, figs. 1 and 2, pi. VI, figs. 1, 2, 2a, pi. VII, figs. 1, la, lb, 

 pi. VIII, figs. 1, 2, 3 and figures of leg and foot bones. 



Titanotherium angustigenis, Osborn, 1896. The Cranial Evolution of Titanotherium, Bulle- 

 tin Amer. Mus. Nat. Hist., vol. VIII. p. 184. 



Megaeerops angustigenis, Osborn, 1902. The Four Phyla of Oligocene Titanotheres, idem, 

 vol. XVI, p. 99. 



This species apparently approaches closest to M. coloradensis, Leidy, founded on 

 coossified nasals with horns attached. In the Cypress Hills species the horns are much farther 

 apart, with a flatter surface separating them. Also the nasals, besides being shorter, expand 

 laterally in front instead of narrowing rapidly as in M. coloradensis. 



Cope, in the American Naturalist, 1889, p. 153, made this species the type of Haplacodon, 

 a generic term discarded by him in his later writings. 



The species, of which the full description with figures is given in part I of this volume, 

 is based on two maxillary bones from the same individual, a separate left ramus, and the 

 symphysial part of another jaw. With these were associated, as probably belonging to the 

 same species, an imperfect cranium, and certain separate leg and foot bones. One of the 

 maxillary bones, the left ramu^, and the nasal bones with horns and part of the frontal, were 

 figured in plates V, VI, VII and VIII. In plate VI, figure I, a view from above was given 

 of the coossified nasals shown in side and front view in plate VIII, and belonging to the 

 cranium mentioned above. Through an error in the explanation of plate VI, these nasals 

 (fig. 1) were ascribed to Menodus f americanus, Leidy, instead of to Menodus angustigenis. This 

 error has been repeated in Professsor H. P. Osborn's paper " The Cranial Evolution of 

 Titanotherium," Bull. Amer. Mus. of Nat. Hist., 1896, foot note p. 175. 



