premolar is more complex in that it has two cusps instead of one. In the third premolar the posterior cusp is much better developed, and placed more obliquely than in the corresponding tooth of _Procyon_; the heel is moreover not so broad. The first molar is not preserved, but judging from the size of its roots it was decidedly the longest tooth of the series. The second molar was likewise bifanged but much smaller; it was placed close against the base of the coronoid. The whole jaw has, relatively, a greater depth than that of the Raccoon, and is remarkably straight upon its lower border, whereas in the recent genus it is considerably curved. The condyle is not preserved, and the angle is somewhat damaged, but it was apparently not so strongly inflected as in the Raccoon. The masseteric fossa is deep and prominent, and the coronoid is high and broad. The inferior dental canal is placed higher than it is in the Raccoon, being slightly above the tooth line. The symphysis is relatively deeper and more robust than in _Procyon_, and the chin is heavier and more abruptly rounded. The jaw of _Leptarctus_ differs from that of _Cercoleptes_ in the following characters: the coronoid is broader and of less vertical extent; the condyle is not placed so high; the angle is elevated above the lower border of the ramus, which is straight and not concave as it is in _Cercoleptes_. In the depth of the symphysis and abrupt rounding of the chin the two genera are similar. _Cercoleptes_, moreover, has a moderately deep groove upon the antero-internal face of the canine, but differs from that of _Leptarctus_ in having an external groove as well. _Cercoleptes_ again resembles _Leptarctus_ in having only three premolars in the lower jaw; the middle one, however, has only a single cusp upon the crown, whereas _Leptarctus_ has two. As compared with _Bassaricyon_,[2] the jaw is more robust, shorter and deeper, with a more prominent chin. The two genera differ again in the number of premolars. Altogether, _Leptarctus_ appears to offer a number of transitional characters between the more typical Procyonidae and the aberrant _Cercoleptes_. This is especially to be seen in the proportions of the jaw, the reduction of the number of premolars, the reduction in size of the last molar, as well as the depth of the mandibular symphysis. FOOTNOTES: [1] Extinct Fauna of Dakota. [2] See J. A. Allen's paper, Proc. Phil. Acad., 1876, p. 21. Transcriber's Note: "Quartenary" was amended to "Quaternary" in the first paragraph.