Fig. 4. Dorsal vertebra of a species of Embolophorus, one-half natural size; right side; a, from front; b, from below; ic, intercentrum; ca, capitular rib articulation.

Fig. 5. Astragalus of individual figured in fig, 4, one-half natural size; from below, ca, ca, facets for calcaneum; na, do. for navicular; tib. 2, do. for bone of spur, or os tibiale. 5a, same bone from external or calcaneal border; ƒ, fibular facet. 5b, same bone, proximal or fibular extremity.

Fig. 6. Left posterior foot of Clepsydrops natalis Cope, superior side, and 6a, inferior (plantar) side, two-thirds natural size. as, astragalus; ca, calcaneum; na, navicular bone; cu, cuboid; euc, mc and ecc, entocuneïform, mesocuneiform and ectocuneiform bones, respectively. I, II, III, IV, V, metatarsals. Tib. 1, Probable tibial facet. In this specimen the calcaneum is displaced; being turned backwards, so as to present its two astragalar facets (asf) anteriorly.

N. B. The use of this plate was kindly granted by the American Philosophical Society.

ON THE STRUCTURE OF THE FEET IN THE EXTINCT ARTIODACTYLA OF NORTH AMERICA. By Prof. E. D. COPE, Philadelphia, Pa. THE structure of the feet of a number of the Artiodactyles of the tertiary beds of North America has already been described. In this paper I enumerate these, and add descriptions of some types which have been hitherto unknown. I commence with the Buno.donta.

BUNODONTA.

Pantolestes Cope. The structure of the tarsus only of this Eocene genus is known. The cuboid and navicular bones are distinct from each other and from the cuneiforms, and the ecto- and mesocuneiform are coössified. There are four metatarsals. The laterals (ii and v) are slender; and the medians are distinct but appressed, their adjacent sides being flattened. This foot structure is remarkably advanced considering the early age, Wasatch Eocene, of the period of its existence, and the primitive tritubercular bunodont character of the superior dentition. The selenodont types which appear first in our series of formations, the Oreodontidæ of the White River low Miocene, present a much more primitive type of foot. The camel series is remarkable for the early and continued absence of the first and fifth metapoidal bones. The first known of the line, Poëbrotherium, from the White River beds, has only minute rudiments of them. It is probable the Pantolestes or some member of the Pantolestidæ is an ancestor of Poëbrotherium with a number of lost types intervening.

1 Cope, Proceedings American Philosophical Society, 1881, p. 188. Paleontological Bulletin, No. 34.

Elotherium Aym.

The

The first information respecting the structure of the feet of this genus was furnished by Marsh.2 He says, "The radius and ulna were separate or very loosely united. third and fourth metacarpals were nearly equal in size, and the second and fifth larger than the corresponding bones of the pes. In the latter the first digit was wanting, and the fifth rudimentary." This description leaves us in the dark as to the development. of the second digit in the posterior foot, and of the second and fifth in the anterior foot. This ambiguous language led me to infer that there are four digits of the anterior foot of the animal described by Marsh, and hence to separate it generically from Elotherium. The first definite information is derived from Kowalevsky from his great memoir on the genus Anthracotherium.3 He here states distinctly the genus is bidigitate, but with small rudiments of the second and fifth metapoidal bones. He shows also that the lunar is equally supported by the magnum and unciform. In a memoir especially devoted to this genus he also shows that the cuboid, navicular and cuneiforms are distinct, while the ecto- and mesocuneiforms are coössified; the entocuneiforms being absent. The structure of the tarsus in this genus is then as in Pantolestes, and from this genus, or one of the same family, Elotherium no doubt took its origin, through intermediate genera.5

SELENODONTA.

Oreodon Leidy. We owe to Leidy the following statement regarding the foot-structure of this genus. "What are supposed to be the bones of the forearm and leg are discrete, as in the hog; and the bones of the feet correspond in number with those of this animal. In 1873 Professor Marsh confirmed these statements as regards the metacarpal bones," and added that "the navicular and cuboid bones were loosely coössified or separate." In 18848 I gave a full account of the structure of the limbs in this genus. I mentioned a peculiar feature of the carpus, viz., that the os lunare is

2 American Journal Sci. Arts, 1873, p. 487, June. Palæontographica, 1873. p. 188. August?

Loc. cit. XXII, N. F. II, 7 p. 415.

I have given the structure of the anterior leg in Elotherium imperator Bulletin U.S. Geol. Surv. Terrs., Vol. V, p. 60.

Extinct Mammalia, Dakota and Nebraska, 1869, p. 72.

7 Amer. Jour. Sci. Arts, p. 409; Marsh does not credit Leidy with his previous ob

servations.

Proceeds. Amer. Phil. Soc. Pal. Bulletin, No. 38, pp. 508-10.

supported below by the inward extension of the unciform, so that the magnum is below the scaphoideum. I also showed that the cuneiforms are distinct, and that the entocuneiform is wanting.

Eucrotaphus Leidy. I have already stated that this genus is tetradactyl anteriorly and posteriorly. I now add that the structure of the limbs and feet is in other respects like that of Oreodon. This is true of the inner extension of the unciform so that the magnum is below the scaphoideum. The inner side of the latter bone in the Eucrotaphus pacificus is so excavated, that there was plainly a free trapezium of small size. In the posterior foot the entocuneiform is wanting, and the mesocuneiform is distinct from the ectocuneiform.

Merycochorus Leidy. The first information of the foot structure of this genus is contained in my paper on the Oreodontidæ above cited.10 The fore and hind feet are there stated to be tetradactyl. I now add that in the M. montanus Cope the os magnum is entirely below the scaphoid, and that there is a distinct trapezium. The posterior foot is constituted as in Eucrotaphus. I also observe that the navicular has a peculiar little facet on its distal face near the front of its external edge. This fits a corresponding facet which forms the proximal surface of a ledge, which extends from front to rear on the inner side of the cuboid. In Eucrotaphus pacificus the arrangement is similar, excepting that the ledge of the cuboid is interrupted at the middle by a deep excavation. In Merychyus arenarum the cuboid is like that of Merycochoerus montanus, in regard to this ledge.

Merychyus Leidy. The limbs and feet in this genus are quite as in Merycochorus. The species which I have examined is the M. arenarum Cope.

Leptomeryx Leidy. We possess as yet no information regarding the limbs and feet of this genus. It is therefore fortunate that I obtained in the White River bed of northeastern Colorado in 1879, a nearly entire skeleton of the L. evansi Leidy. The bones were all found close together, and belong to two individuals, and are without admixture of those of any other species.

From these, and inferentially from other specimens, is derived the curious fact, that there are four distinct metacarpals, all supporting digits, while there are but two metatarsals, which are

Loc. cit., p. 504.

10 Proceeds. Amer. Philosoph. Society, 1884, p. 501.

coössified into a cannon bone. This diversity between the limbs is unparalleled, although an approach to such a condition is seen in the peccary. In this animal, as is well known, there are four distinct digits in the manus, while in the pes, the metatarsals are coössified proximally, and the fifth metatarsal is reduced to a scale. This difference between the two limbs is a further illustration of Mr. Ryder's statement that the posterior limb is in advance of the anterior in grade of development, for which I have endeavored to account by reference to the fact that it is the posterior foot which receives the greater number of impacts in progression. This is because the hind limb is the principal propeller of the body.

In accordance with the structure of the feet, the fore limb is much behind the posterior limb in the fixity of its parts. The ulna and radius are distinct; the head of the latter is a regular transverse oval.

The lunar is mainly supported by the unciform, so much so that the front face of the magnum is not bevelled to fit the former. Behind the face, the edge of the magnum is a little bevelled for the lunar; but the former bone lies almost entirely under the scaphoid. The trapezoides is coössified with the magnum. No distinct trapezium.

The distal extremity of the fibula is not coössified with the tibia, but forms a separate bone, as in the Ruminantia.

The cuboid and navicular are solidly united. The ecto- and mesocuneiforms are distinct, and there is no entocuneiform. The second metatarsal is represented by a flat oval bone, which is borne on the underside of the projecting heel of the third metatarsal. The fifth is of smaller size, and is a scale embedded in a depression of the posterior part of the side of the fourth. Ungues unilateral, trihedral and acute.

Hypertragulus Cope. Remains of this genus are as abundant in the White River beds as are those of Leptomeryx, and like that genus I know but one species, the II. calcaratus Cope. Unfortunately I have not been able to obtain bones of the skeleton connected with dentition from this formation, although numerous bones occur separately which probably belong to it. The genus is however abundantly represented in the John Day Miocene beds of Oregon, where Leptomeryx does not probably occur. At least no specimens of the latter are to be found in a collection of between one and two hundred individuals of this general type in my

supported below by the inward extension of the u that the magnum is below the scaphoideum. I also s the cuneiforms are distinct, and that the entocuneiform

Eucrotaphus Leidy. I have already stated that t tetradactyl anteriorly and posteriorly.9 I now add th ture of the limbs and feet is in other respects like that This is true of the inner extension of the unciform magnum is below the scaphoideum. The inner side bone in the Eucrotaphus pacificus is so excavated, th plainly a free trapezium of small size. In the pos entocuneiform is wanting, and the mesocuneiform is the ectocuneiform.

Merycochoerus Leidy. The first information of ture of this genus is contained in my paper on t above cited.10 The fore and hind feet are there st dactyl. I now add that in the M. montanus Cope is entirely below the scaphoid, and that there is zium. The posterior foot is constituted as in also observe that the navicular has a peculiar distal face near the front of its external edge. sponding facet which forms the proximal surface extends from front to rear on the inner side Eucrotaphus pacificus the arrangement is simi the ledge of the cuboid is interrupted at the excavation. In Merychyus arenarum the cul Merycochoerus montanus, in regard to this led.

Merychyus Leidy. The limbs and feet in t as in Merycochorus. The species which I h M. arenarum Cope.

Leptomeryx Leidy. We possess as yet no ing the limbs and feet of this genus. It is th I. obtained in the White River bed of r 1879, a nearly entire skeleton of the were all found close together, and are without admixture of those