PEKISS0DACTYL4. 
317 
only referred to it provisional!}^, as the number of the premolar teeth is not 
yet known in either. The known sj^ecies have only been found in the beds 
of the Lonp Fork epoch. 
The four known species may be distinguished as follows: 
*Eamns maudibuli shallow and stout; last molar close to base of coronoid pro¬ 
cess . -... A. crassus. 
**Earaus mandibuli compressed; deeper: 
tBase of coronoid process flat in front, with lateral angles : 
Last molar at base of coronoid process; symphysis and external incisors 
small... A. meridianus. 
Last molar well in front of base of coronoid process; symphysis and external 
incisors large..'. A. megalodus. 
tt Base of coronoid process convex in front without lateral angles: 
Last molar largest, not close to base of coronoid.... .A. jemezamis. 
Aphelops meridianus, Leidy. 
Plates Ixxiii, figs. 1-2; Ixxiv, figs. 1-3. 
Ehinocerus meridianus, Leidy, Extinct Mammalia of Dakota and Nebraska, p. 229. 
Aphelops meridianus, Cope, Ann. Eept. Chief of Engineers, 1875, ii, p. 991. 
The A. meridianus was first described from a superior molar tooth from 
Texas. The corresponding molar in the New Mexican species does not 
differ from it. The general characteristics of this almost unknown species 
may then be learned from our specimens. Li general features, it much 
resembles the A. megalodus, but there are nurnerous differences. There is 
a considerable protuberance of the anterior border of the posterior trans¬ 
verse crest, nearer the outer border of the crown than the protuberance of 
the posterior border of the anterior transverse crest. These give the trans¬ 
verse valley a sigmoid form, which is not seen in A. megalodus. There is no 
posterior protuberance of the anterior transverse crest of the last superior 
molar. There is a strong anterior basal cingulum on the true molars, and 
a very strong elevated cingulum connecting the inner ends of the transverse 
crests, but not passing round the interior extremities of the crests. It is rep¬ 
resented in the last two molars by a small tubercle. There are no external 
cingula. The external faces of the superior molars present a convexity for¬ 
ward, which is very prominent in the true molars, each overlapping the pre¬ 
ceding tooth. Immediately behind and parallel with this ridge is a groove, 
which is followed by a low ridge bounding the general external surface in 
