Cope.] 882 {April 15, 
North America and Europe; Pachynolophus, Hyrachyus, Hyracothe- 
rium, Pliolophus. 
Europe only ; Lophivdon, Lo- 
phiothertum. 
Four of the genera ascribed 
to North America have come un- 
der my observation. 
TRIPLOPID 2. 
Cope, American Naturalist, 
1881, April (March 25th), p. 340. 
But one genus of this family 
is known at present, but the 
irae number will probably be in- 
Fig. 1. Part of lett maxillary bone of creased when the structure of 
Penola aingularis Cope; from the the feet of various imperfectly 
Wasatch beds of New Mexico, from Capt. 
’ Wheeler’s report iv ii pl. Ixvi. known species is ascertained. 
TRIPLOPUS Cope. 
American Naturalist, 1880, p. 383 (April 27th). 
Dental formula, I. ?; C.4; P-m.; 4; M. #; a considerable diastema 
anterior to the first premolar. Molars with only two vertical external 
ridges, the anterior cingular and the approximated median of the anterior 
crescent. Transverse crests two, uninterrupted and rather oblique; a 
? third and short crest, on the posterior base of the first true molar. Pre- 
molars different from molars, the third and fourth with two transverse 
crests. Inferior molars with two transverse crests, as in Lophiodon, the 
last without heel. 
An ossified inferior wall of the meatus auditorius externus. Posttym- 
panic and paroccipital processes distinct form each other. No postorbital 
arch. Postparietal and mastoid foramina preserved; the latter large. 
Cervical vertebree rather long; axis with subcylindric odontoid process. 
Scapula with small coronoid process. Great tuberosity of humerus long, 
curved. No trochlear crest on condyles of humerus ; epicondyles rudi- 
mental. Ulna and radius distinct throughout their length ; ulnar articula- 
tion with carpus, small. Trapezoid bone of carpus with a facet for the 
trapezium. Unciform with two inferior facets. Metacarpals three principal 
ones, and one, the fifth, rudimental ; the distal extremities of the second 
and fifth opposite ; the third a little longer. 
The dentition of this genus is nearly that of Hyrachyus. The only ex- 
ception is the possible third transverse crest of the first true molars*. The 
other portions of the skeleton known, are also much like those of 
Hyrachyus, with the exception of the number of digits of the anterior foot. 
The entirely rudimental character of the fifth metacarpal, which with its 
*This point is further considered in the description of ‘the species. 
