ENTELODONTS FROM THE BIG BADLANDS OF SOUTH DAKOTA IN THE GEOLOGICAL MUSEUM OF PRINCETON UNIVERSITY. INVESTIGATION AIDED BY A GRANT FROM THE MARSH FUND OF THE BY WILLIAM J. SINCLAIR. (Read April 22, 1921.) I had always assumed that entelodonts were rare fossils in the White River Oligocene until last summer when the Princeton Expedition to South Dakota, within an area of about two square miles in the valley of Indian Creek, in Pennington County, between July 14 and 27, collected five skulls and two lower jaws belonging to three species of Archæotherium and noted, but refrained from collecting, perhaps as many more fragmentary specimens within the same area. This mass of new material made it desirable to restudy the Princeton entelodont collection as a whole, as much of it had never been adequately determined. Fortunately, the timely appearance of Mr. Troxell's1 excellent paper on the entelodonts in the Marsh collection at Yale greatly facilitated these studies. Whether certain of the characters used in the classification of these animals are of specific importance or of the nature of secondary sexual structures can not yet be determined. For the present it is safer to give a separate specific name to each well-defined variant, based on adequate material, than to group together forms which may have been rapidly mutating and thereby developing differences of the first degree of importance for detailed faunal and stratigraphic studies. A review of the genera and species represented follows. 1 Am. Jour. Sci., Vol. L., Nov.-Dec., 1920, pp. 243-255, 361-386, 431-445. PROC. AMER. PHIL. SOC., VOL. LX., EE, MARCH 17, 1922. I. FROM THE TITANOTHERIUM BEDS. Archæotherium scotti sp. nov. In 1895 Professor Scott2 announced the discovery of the classic specimen now known as No. 10885 and mounted in the Geological Museum of Princeton University. This almost complete and unique skeleton (not "two almost complete skeletons" as mistakenly stated in the preliminary report) was found in the summer of 1894 by Mr. H. F. Wells in the upper Titanotherium beds in Corral Draw, South Dakota (whether in Pennington or Washington Counties does not appear), was secured by Mr. J. B. Hatcher and excavated by him May 11, 1894, and was referred by Professor Scott, in his announcement to the International Zoological Congress at Leyden, to Leidy's FIG. 1. Archæotherium scotti sp. nov. Holotype, No. 10885. Three-quarter view of the skull and jaws from the left side, in the position in which it stands on the mounted skeleton, approximately one-sixth natural size. Drawn from photograph and the specimen. 2 W. B. Scott, "Compte-Rendu des Séances du Troisième Congrès International de Zoologie," Leyde, 16-21 Septembre, 1895. Leyde, E. J. Brill, 1896. Elotherium ingens, "without paying much attention to the species," as he has since told me. 3 Elotherium ingens, as originally constituted, is a composite, comprising "fragments found in association with the fossils of Elotherium mortoni in the Mauvaises Terres, which appear too large to belong to this species, even making allowance for a considerable range in size." These were from the collection of Dr. Hayden, did not pertain to a single individual and were from unknown horizons. The first to be mentioned by Dr. Leidy3 is the "fore part of the lower jaw, in advance of the second premolars," which therefore becomes the type specimen of Elotherium (=Archæotherium) ingens. In the light of what is at present known regarding the larger entelodont species of the White River Oligocene, the various fragments included by Leidy with the type of ingens are specifically indeterminate, since the latter retains no teeth. A suggestion of Mr. Troxell's, in a personal letter, first called my attention to the possibility that our Princeton specimen represented a new type and, on reviewing the subject, I agree with him that the mandibular fragment figured by Leidy in front view on Plate XXVII., Fig. 10, of the "Extinct Mammalian Fauna," copied here on a smaller scale as Fig. 4, differs both in size and structure from the corresponding part of the specimen monographed in detail by Professor Scott, for which I now propose the new name Archæotherium scotti (Figs. 1, 2, 3, 22), characterizing it as follows: 1. Very long and thick dependent malar process directed downward, forward and outward (the latter curvature probably intensified by crushing), with thin sinuous anterior margin and greatly thickened, round-edged, club-like posterior distal end, projecting so far below the anterior distal end of the process that the latter seems to contract in breadth a second time after a minimum of 88 mm. and a maximum of 114 mm. The greatest thickness of the enlarged end is 46 mm. The outer face of the process is convex transversely at the narrowest part, convex behind and flat in front at the widest 3 J. Leidy, "The Extinct Mammalian Fauna of Dakota and Nebraska," Jour. Acad. Nat. Sci. Phila.. Vol. VII., Second Series, p. 192, 1869. "The Osteology of Elotherium," Trans. Am. Phil. Soc., Vol. XIX., pp. 273-324. Pls. XVII., XVIII., 1898. expansion and concave longitudinally, accentuated by crushing. Its front margin, at the point of greatest expansion, is in line with the posterior border of the orbit. FIG. 2. FIG. 3. FIG. 4. FIG. 2. Archaeotherium scotti sp. nov. Holotype, No. 10885. Anterior mental process of the right side, seen from directly in front, one quarter the natural size. FIG. 3. Archæotherium scotti sp. nov. Holotype, No. 10885. rior mental process from below, one quarter the natural size. proper orientation, the drawing should be held overhead in an sition and viewed from below. Right anteTo get the inverted po FIG. 4. Archæotherium ingens Leidy. Holotype. The front of the lower jaw showing the dependent processes. Copied from Leidy's figure, one quarter the natural size. 2. The zygomatic arch is 46 mm. wide at its narrowest part and the jugal process is very thin, and, while it extends to the front edge of the glenoid fossa, it takes no part therein and is not visible in side view, but only from below, as shown by the deep shading in Fig. 1. 3. Pï seems to have been double-rooted, judging from extremely slight indications of a median constriction across the alveolus, but it would be equally permissible to assume that the roots were conjoined, with merely a groove extending lengthwise between them. The empty alveolus measures 28 x 19 mm. 4. The anterior mental processes are very large and extremely broad at the base, anteroposteriorly (Fig. 3), but vertically the neck is only 20 mm. thick at the middle, thinning out to an edge front and rear. Distally, the process swells out to an oval bulb 61 x 36 mm. in diameters and curves outward, backward and upward (in part due to crushing). So far as can be determined from the figure of A. ingens (Fig. 4), the corresponding structure seems to have |