Cope.] 484 [Sept. 17, 
On some Mammalia of the Lowest Eocene beds of New Mewico. By EB. 
D. Cope. 
(Read before the American Philosophical Society, Sept. 17, 1881.) 
MESONYX NAVAJOVIUS, sp. nov. Smaller than the two known species, and 
with the crowns of the molars more compressed and the blades of the 
heels of the inferior series more acute. Molars seven, the first one-rooted. 
Last molar with a cutting heel like the others, and with the penultimate, 
with a rudimental anterior inner cusp. All the molars with an anterior 
basal tubercle except the first, second and third. No basal cingula. 
Principal cusp elevated and compressed, as in the premolars of Oxyona. 
Enamel minutely rugose. Mandibular rami and inferior canine teeth com- 
pressed, the angle of the latter not inflected. Length of inferior molar 
series M. .078 ; do. of premolar series .046 ; fourth premolar, length of base 
.010; elevation of cusp .008; second true molar, length .012, elevation 
.010; width of heel .005; depth of ramus at .020; diameter of base of 
crown of canine, vertical .009. 
PERIPTYCHUS CARINIDENS, gen. et. sp. nov. Creodontium. Char. Gen. 
No distinct sectorial teeth, the first and second true inferior molars simi- 
lar. They support a principal median cusp, a broad heel and a prominent 
anterior cingulum. The heel is more or less divided into tubercles ; the 
anterior cingulum is on the inner side, and represents the anterior cusp of 
a sectorial tooth. On the inner side of the principal cusp a cingulum rises, 
forming a flat internal tubercle. Last molar not smaller than the others ; 
premolars unknown. 
This genus belongs to the Amblyctonide with Amblyctonus and Pale- 
onyctis. It differs from both in the rudimental character of the anterior 
cusp, and from the former, in the presence of the internal tubercle. In 
Mesonyzx the heel has a median cutting edge. Char. Specif. Parts of both 
mandibular rami and the shaft of a humerus represent this species. They 
indicate an animal of the size of the red fox, but much more robust. The 
mandibular ramus is rather shallow and thick, and the molars are not large. 
The heel of the penultimate supports three tubercles, of which the ex- 
ternal is the largest. The anterior cingulum supports a small cusp, and 
then rises to the internal tubercle, which is compressed. The sides of all 
the cusps are marked with distinct, well separated, vertical ridges. Each 
extremity of the internal cusp is connected with the principal cusp by a 
ridge. The first true molar has fewer cusps. Those of the heel are 
scarcely distinct, and form a border which rises prominently into the flat 
internal tubercle, which forms a narrow longitudinal blade. The anterior 
cingulum has no cusp and does not rise into the inner tubercle. The prin- 
cipal cusp has a strong entering groove next the inner tubercle. Length 
of crown first molar .0115; width of do. .006; elevation of do. .006. 
Length of second molar .011; width of do. .007; elevation of do. 
-0065. Depth of ramus at do. .020. The species is a good deal smaller 
than the Amblyctonus sinosus. 
