Cope.] 484 [Sept. 17, 



On some Mammalia of tlie Lowest Eocene teds of Neio Mexico. By E. 



D. Cope. 



{Read tefore tite American PMlosopliical Society, Sept. 17, ISSl.) 



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 penviltimate, 

 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 Oxycena. 

 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 .030 ; diameter of base of 

 crown of canine, vertical .009. 



Periptychus carinidens, gen. et. sp. nov. Creodontium. Cheer. 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 Amblyctonidce with Amilyctonus and Palm- 

 onyctis. It difters from both in the rudimental character of the anterior 

 cusp, and from the former, in the presence of the internal tubercle. In 

 Mesonyx 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 mai'ked with distinct, well separated, vertical ridges. Each 

 extremity of the internal cusp is connected Avith the principal cusp by a 

 ridge. The first true molar has fewer cusids. 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. .030. The species is a good deal smaller 

 than the Amhlyctonus sinosus. \ 



