_On the Affinities of Leptarctus primus of Leidy. _

By J. L. WORTMAN. 

_AUTHOR'S EDITION, extracted from_

BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY, VOL. VI, ARTICLE VIII, pp. 229-231. 

_New York, July 30, 1894. _

Article VIII. --ON THE AFFINITIES OF LEPTARCTUS PRIMUS OF LEIDY. 

By J. L. Wortman. 

Up to the present time but very little has been known of the existenceof the peculiarly American family Procyonidæ in any deposits olderthan the very latest Quaternary. Leidy has described and figured[1] anisolated last upper tooth, from the Loup Fork deposits of Nebraska, under the name of _Leptarctus primus_, which has been referred to thisfamily. The Museum Expedition of last year into this region wassuccessful in obtaining additional material, which we provisionallyrefer to Leidy's species. 

=Leptarctus primus= _Leidy_. 

The specimen consists of the right ramus of the lower jaw, carryingthe third and fourth premolars and the canine. The condyle is brokenaway, but the coronoid process and the angle are preserved. Thespecimen is from a young individual in which the last premolar hadjust cut the gum. The alveoli of all the other teeth are present andin a good state of preservation. 

The dental formula is as follows: I. _3, C. _1, Pm. _3, M. _2. Theincisors are not preserved, but their alveoli indicate that they weremuch crowded, the outside one being placed almost directly in front ofthe canine, and the middle one pushed back considerably out ofposition. This series is in marked contrast with that of the Raccoon, in which the crowns of the incisors form almost a straight line acrossthe jaw, and the middle one is crowded backwards to a very slightextent. The canine is peculiar and differs markedly from that of theRaccoon. It is rather robust, very much recurved and grooved by a deepvertical sulcus upon its antero-internal face. This sulcus is butfaintly indicated in the Raccoon. The postero-external face of thecrown is marked by a sharp ridge which becomes more prominent near theapex. The first premolar is not preserved, but its alveolus indicatesthat it was a single-rooted tooth, placed behind the canine after theintervention of a very short diastema. The second premolar isbifanged; its crown is composed of a principal cusp, to which is addedbehind a small though very distinct second cusp. There is in additionto these cusps a distinct basal cingulum, most prominent in the regionof the heel. The third premolar, like the second, is double rooted;its crown moreover is made up of two cusps, the posterior being almostas large as the principal one. These cusps do not stand in the line ofthe long axis of the jaw, but are placed very obliquely to it. Theheel is not very prominent, but the basal cingulum is well developed, both in front and behind. As compared with the Raccoon, the secondpremolar is more complex in that it has two cusps instead of one. Inthe third premolar the posterior cusp is much better developed, andplaced 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 itsroots it was decidedly the longest tooth of the series. The secondmolar was likewise bifanged but much smaller; it was placed closeagainst 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 inthe recent genus it is considerably curved. The condyle is notpreserved, and the angle is somewhat damaged, but it was apparentlynot so strongly inflected as in the Raccoon. The masseteric fossa isdeep and prominent, and the coronoid is high and broad. The inferiordental canal is placed higher than it is in the Raccoon, beingslightly above the tooth line. The symphysis is relatively deeper andmore robust than in _Procyon_, and the chin is heavier and moreabruptly rounded. 

The jaw of _Leptarctus_ differs from that of _Cercoleptes_ in thefollowing characters: the coronoid is broader and of less verticalextent; the condyle is not placed so high; the angle is elevated abovethe lower border of the ramus, which is straight and not concave as itis in _Cercoleptes_. In the depth of the symphysis and abrupt roundingof the chin the two genera are similar. _Cercoleptes_, moreover, has amoderately deep groove upon the antero-internal face of the canine, but differs from that of _Leptarctus_ in having an external groove aswell. _Cercoleptes_ again resembles _Leptarctus_ in having only threepremolars in the lower jaw; the middle one, however, has only a singlecusp upon the crown, whereas _Leptarctus_ has two. 

As compared with _Bassaricyon_, [2] the jaw is more robust, shorter anddeeper, with a more prominent chin. The two genera differ again in thenumber of premolars. 

Altogether, _Leptarctus_ appears to offer a number of transitionalcharacters between the more typical Procyonidæ and the aberrant_Cercoleptes_. This is especially to be seen in the proportions of thejaw, the reduction of the number of premolars, the reduction in sizeof 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.