488 GEOLOGICAL SUKVEY OF THE TEREITOEIES. 



lieasKrements. 



M. 



Length from posterior rim of temporal fossa to middle of osseous eyebrow 0.472 



Least width of parietal plane 104 



Superciliary width 260 



Elevation of born-core 050 



Length of free nasal bones 010 



Width of free nasal bones at base 010 



Symborodon ACER, Cope, Proceed. Amer. Assoc. Adv. Sci., 1873, 



109 5 Synop. New Vert. Ool., 13. Megaceratops acer, Cope, Pal. 



Bui., 1873, No. 15, 4. 



Another huge mammal, second only to the preceding in size, but more 

 formidably armed, was its contemporary. It is represented in my collec- 

 tion chiefly by the entire upper portion of a cranium ; the greater jiart 

 of a skeleton, with upper part of cranium and lower jaw with teeth ; 

 and by portions of skeleton, with horns, of a third. Top of head con- 

 cave longitudinally, somewhat convex between the orbits, and flat, 

 forming a narrow plane between the temporal fossae ; latter produced 

 backward. Orbit not inclosed behind; an overhanging superciliary 

 ridge. Nasals exceedingly short and massive, abruptly decurved, each 

 supporting a large acute horn-core, which is connected with its fellow 

 by a ridge at the base, and diverges widely from it, with an outward and 

 forward curve to the acutely-compressed apex. Each horn-core com- 

 posed externally of the ascending portion of the maxillary bone as 

 high as some distance above the base of the nasals. Nasals abruptly 

 contracting to a stout subangular apex. Zygomatic arch deep. 



Mandibular ramus massive, and in every respect stouter than in S. 

 hucco, and similarly without incisor-teeth. 



Measurements. 

 No. 1. 



M. 



Length of cranium, (35 inches) ^ 0.895 



Length from posterior rim of temporal fossa to middle of superciliary ridge. . . . . .345 



Width of front between eyebrows 210 



Length of horn-core on inner side, (10 inches) 254 



No. 2. 



Length of first and second molars 135 



Width of second inferior molar 040 



Depth of ramus at second inferior molar 123 



This was a truly formidable beast, exhibiting a position of the horns 

 strangely the reverse of that seen during the present period. Its size 

 exceeded that of the, Indian rhinoceros. • 



Symborodon trigonoceras, Cope, Synop. New Vert. Col., 1873, 13. 



JBrontotherium trigonoceras, Marsh, Amer. Nat., 1874, p. . 



A species similar in size to the last, but presenting peculiarities not 

 shared by any other species of the genus. The first of these is the strong 

 basal cingulum on the inner side of the premolars, which is continued in 

 a less prominent form between the bases of the cones of the molars. The 

 bases of the cones of the premolars are strongly plicate. The horns rise 

 from a basis which is anterior to the orbit, and are short and very stout. 

 They are triquetrous, with the fa,ces interior, posterior, and latero- 

 anterior, and are directed outward and upward. Their extremities are 

 coars.'ly rugose and subtriangular, sending an apex toward the middle 

 line, and decurved convex outwardly. The vertex and front are a con- 



