IGG ON THE EXTINCT MAMMALIA OF 



Sheyenno River. According to Dr. Ilayden, the remains of Leptomeryx Evansi 

 belong to beds B and D of his section of the tertiary formations of Dakota and 

 Ncbraslva. 



The slvull in size and form approaches most that of the hving Musks. The best 

 preserved specimen under examination, represented in figures 1 — 4, plate XIV, has 

 the intermediate portion of the cranium and the anterior extremity of the face 

 destroyed. 



Lateral vieio of the skull, figure 1, j)lale XIV. — The cranium back of the orbits is 

 proportionately longer and wider, but lower than in the Musks. The temporal foss33 

 are proportionately longei', and their long diameter is antero-posterior as in the Deer, 

 instead of oblique as in the former. As in these, they are separated posteriorly by a 

 short sagittal crest, though proportionately longer than in them. Their anterior 

 boundary is more vertical, and even inclines slightly backward in its descent, instead 

 of forward as in the Musks. Posteriorly they are defined from the inion by an acute 

 ridge, more oblique from the pei'jDendicular than in the latter. See figures 1, 2, 

 plate XIV. 



The zygoma is much stronger than in the Musks, and indeed is proportionately 

 more so than in existing ruminants generally. 



The temporal fossa of Leptomeryx is about twice the length of the depth. It pre- 

 sents a uniform convex surface, becoming concave only in approaching the superior 

 and posterior defining ridges. 



The zygomatic fossa is proportionately more capacious than in the Musks. The 

 zygoma starts directly outward from its posterior root about the middle of the 

 position of the temporal fossa. It is then directed very abruptly foi'ward, more like 

 in the Hog and Peccary than in recent ruminants, and proceeds gently downward to 

 the face. It is constructed as in the Musks and Deer, and presents a wide, external 

 vertical face two and a half lines in depth. 



The orbits are proportionately rather smaller than in the Musks, and occupy 

 nearly the same relative position as in these, the an1>orbital margin being on a line 

 with the fore part of the first true molar tooth. The orbital entrance is quadrately 

 oval, with the transverse diameter rather greater than the vertical, but it is more 

 oblique, with both a greater upper and forward inclination than in the Musks. 



Two specimens under examination appear to indicate that the post-orbital arch is 

 interrupted for a short distance. The frontal contributes a longer process to the arch 

 than the malar, and both processes end in roughened points about a line apart 

 inwardly, and widening outwardly to about twice that distance. See figure 1, 

 plate XIV. 



The ant-orbital margin presents a strong lachrymal process, proportionately much 



