PERISSODACTYLA. 
319 
of the zygomatic process is the meatus auditorus externus. It is presented 
upward and outward, and is not closed below superficially, but is continued 
into the fissure between the postglenoid and mastoid processes. The latter 
is rather narrow antero-posteriorly, and extends as far inferiorly as the 
glenoid articular surface. 
Length of the series of seven superior molars ...... 0.237 
Length of the three true molars... 0.123 
Length of the last true molar...... 0.037 
Width of the same...... 0.04G 
Length of the first true molar..... 0.051 
Width of the same..... 0.057 
Length of the second premolar... 0. 029 
Width of the same. . 0.033 
Total length of the ramus mandibuli.... 0.455 
Length of the s.vmphysis .. 0.114 
Width of the symphysis...... 0.058 
Diameter of the external incisor .. 0.015 
Diameter of the internal incisor.. 0.005 
Depth of the ramus at the second premolar... 0.002 
Depth of the ramus at the third molar. 0.080 
Width of the inferior border of the ramus at the middle... 0.035 
Length of the series of inferior molars..... 0.220 
Length of the series of three true molars.. 0.125 
Length of the third premolar. 0.037 
Width of the grinding-face of the same. 0. 020 
Length of the penultimate molar.... 0.042 
Width of the grinding-face of the same. 0.025 
Length of postglenoid process.... 0. 050 
Width extero-internally... 0. 030 
Width of the mastoid process postero-exterually. 0.029 
These measurements indicate a size similar to that of the Bhinocerus 
sumatranus. 
Aphelops jemezanus, Cope. 
Plates Ixsiii, figs. 3-4; Ixxiv, fig. 4. 
Ann. Kept. Chief of Engineers, 1875, ii, p. 992; Proc. Phila. Acad., 1875, p. 200. 
That a second species of Rhinoceros, even larger than the other species 
of Aphelops, formerly existed in the region of New Mexico, is demonstrated 
by a right mandibular ramus, obtained, by Dr. H. C. Yarrow, from near 
'the town of Santa Clara, on the west side of the Rio Grrande. The speci¬ 
men, in its present condition, includes the condyle, angle and ramus as far 
