p. 229-231 ; 24 cm.Includes bibliographical references

Leidy, Joseph, 1823-1891.

Wortman, Jacob Lawson.

American Museum of Natural History Scientific Publications

Article VIII.-ON THE AFFINITIES OF LEPTARCTUSPRIMUS OF LEIDY.By J. L. WORTMAN.Up to the present time but very little has been known of theexistence of the peculiarly American family Procyonide in anydeposits older than the very latest Quartenary. Leidy hasdescribed and figured' an isolated last upper tooth, from theLoup Fork deposits of Nebraska, under the name of Leptarctusprirnus, which has been referred to this family. The MuseumExpedition of last year into this region was successful in obtain-ing additional nmaterial, which we provisionally refer to Leidy'sspecies.Leptarctus primus Leidy.The specimen consists of the right ramus of the lower jaw,carrying the third and fourth premolars and the canine. Thecondyle is broken away, but the coronoid process and the angleare preserved. The specimen is from a young individual in whichthe last premolar had just cut the gum. The alveoli of all theother teeth are present and in a good state of preservation.The dental formula is as follows: I. 3, C. -, Pm. 3, M. 2. Theincisors are not preserved, but their alveoli indicate that theywere much crowded, the outside one being placed almost directlyin front of the canine, and the middle one pushed back consid-erably out of position. This series is in marked contrast withthat of the Raccoon, in which the crowns of the incisors formalmost a straight line across the jaw, and the middle one iscrowded backwards to a very slight extent. The canine is pecu-liar and differs markedly from that of the Raccoon. It is ratherrobust, very much recurved and grooved by a deep vertical sulcusupon its antero-internal face. This sulcus is but faintly indica-ted in the Raccoon. The postero-external face of the crown ismarked by a sharp ridge which becomes more prominent near'Extinct Fauna of Dakota.[229]230 Bulletin American Museum of Natural History. [Vol. VI,the apex. The first premolar is not preserved, but its alveolusindicates that it was a single-rooted tooth, placed behind thecanine after the intervention of a very short diastema. Thesecond premolar is bifanged ; its crown is composed of a prin-cipal cusp, to which is added behind a small though very distinctsecond cusp. There is in addition to these cusps a distinct basalcingulum, most prominent in the region of the heel. The thirdpremolar, like the second, is double rooted; its crown moreoveris made up of two cusps, the posterior being almost as large asthe principal one. These cusps do not stand in the line of thelong axis of the jaw, but are placed very obliquely to it. Theheel is not very prominent, but the basal cingulum is well devel-oped, both in front and behind. As compared with the Raccoon,the second premolar is more complex in that it has two cuspsinstead of one. In the third premolar the posterior cusp ismuch better developed, and placed more obliquely than in thecorresponding tooth of Procyon; the heel is moreover not sobroad.The first molar is not preserved, but judging from the size ofits roots it was decidedly the longest tooth of the series. Thesecond molar was likewise bifanged but much smaller; it wasplaced close against the base of the coronoid.The whole jaw has, relatively, a greater depth than that of theRaccoon, and is remarkably straight upon its lower border,whereas in the recent genus it is considerably curved. The con-dyle is not preserved, and the angle is somewhat damaged, but itwas apparently not so strongly inflected as in the Raccoon. Themasseteric fossa is deep and prominent, and the coronoid is highand broad. The inferior dental canal is placed higher than it isin the Raccoon, being slightly above the tooth line. The sym-physis is relatively deeper and more robust than in Procyon, andthe chin is heavier and more abruptly rounded.The jaw of Leptarctus differs from that of Cercole.ptes in thefollowing characters: the coronoid is broader and of less ver-tical extent; the condyle is not placed so high ; the angle iselevated above the lower border of the ramus, which is straightand not concave as it is in Cercoleptes. In the depth of thesymphysis and abrupt rounding of the chin the two genera areI1894.] Wortman on Affinities of Leptarciusprimus. 231similar. Cercoleptes, moreover, has a moderately deep grooveupon the antero-internal face of the canine, but differs from thatof Leptarctus in having an external groove as well. Cercoleptesagain resembles Leptarctus in having only three premolars in thelower jaw; the middle one, however, has only a single cusp uponthe crown, whereas Leptarctus has two.As compared with Bassaricyon,' the jaw is more robust, shorterand deeper, with a more prominent chin. The two genera differagain in the number of premolars.Altogether, Leptarctus appears to offer a number of transitionalcharacters between the more typical Procyonidae and the aberrantCercoleptes. This is especially to be seen in the proportions ofthe jaw, the reduction of the number of premolars, the reduc-tion in size of the last molar, as well as the depth of the man-dibular symphysis.1 See J. A. Allen's paper, Proc. Phil. Acad., I876, p. 2I.

Affinities of Leptarctus primus

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