This cingulum is broken on the inner surface. P3 is very rugose, with a strong external cingulum leading to the well marked tritocone and forming a double ridge anteriorly on the protocone.

A. deflectus can be further characterized, in general, by the form of P2 with its external cingulum, small cuspid dueterocone, and its rounded anterior and pointed posterior ends; by the boldness of the teeth in the manner in which the cusps and cingular ridges stand out; by the position of the posterior nares situated just back of the molars; by the long diastema in front of P2 and the probable absence of P1.

Very extensive lateral crushing has taken place in this type specimen but it is evident that the skull was very narrow originally; across between the orbits the distance is scarcely more than 70 mm. The otic bullæ are elongated antero-posteriorly; the occipital condyles are light, and the supra-occipital is narrow (22 mm.). The face is bent down strongly on the basicranial axis. The paroccipitals form peculiar, strong ridges outside the paramastoid processes; the slender processes are near the condyles and join the bullæ at their bases. The sutures between the frontals and parietals are not marked by ridges. Marsh has pointed out that the postorbital processes are long and more nearly close the orbit behind than is usual.

The lower jaws of A. deflectus (fig. 7) are most interesting in the number of small tubercles and interrupted cingula around and between the lobes of the teeth. The purpose of these seems to be to retard the movement of food when the long points of the superior molars press down between the lobes.

3

On the inner side of the talonid of M, is a cingulum made up of a series of cusps; the talonid itself is a single isolated pointed cone. Two exterior basal tubercles lie between the talonid and hypoconid; they appear less conspicuously between the protoconid and hypoconid. Small roughened areas break the transverse valleys and unite adjacent lobes in each case, while a strong cingulum lies anteriorly on the tooth.

4

P1 likewise has an irregular lot of tubercles forming the heel and has sharp ridges running to the point of the protoconid; only the outer side of this cone is smooth. The paraconid marks the beginning of the sharp ridge to the central cone. The tooth measures 21.3 X 13.7 mm.

P is narrow with two straight ridges running to the

2

tip of the protoconid. On each side of the posterior ridge are depressions bounded below by the basal cingulum. The diameters are 20 X 9 mm. P2 is not preserved, but the two rootlets indicate its small narrow form. P, was entirely lacking, or was set near the canine in front of a long diastema, as is indicated by other specimens at hand.

The canine (fig. 7 B) has a very unusual form, which may be considered a flattened cone, with three strong ridges from the front, inner and back sides joining at the apex. Its diameters are 14.6 and 12 mm., the enameled crown being 22 mm. long.

SUMMARY.

The weight of the evidence seems to show that Aymard's genus Bothriodon precedes Ancodus Pomel and Hyopotamus Owen in spite of statements to the contrary.

Our American species, distinct from European forms of this group, may be placed under the following genera: Epinacodon, Elomeryx, Heptacodon, and Octacodon. The first of these is new and is made to include A. deflectus (Marsh), A. americanus (Leidy), and A. rostratus (Scott), species commonly classed under Ancodus.

One new subspecies is here described under the name Elomeryx armatus angustus, and the very complete skull is figured.

ART. XXII.-Palæolagus, an Extinct Hare; by EDWARD L. TROXELL.

[Contributions from the Othniel Charles Marsh Publication Fund, Peabody Museum, Yale University, New Haven, Conn.]

Among the many skeletons of the smaller mammals in the Yale Fossil Vertebrate Collection there are numerous specimens of the fossil rabbits and hares, some of which comprise unusually complete skulls, limbs, and vertebræ. Two distinct species of the genus Palæolagus Cope were secured by Professor Marsh in the early days of vertebrate exploration, one of them the smaller P. haydeni, which varies considerably in size and age characters and may be considered to include specimens of the subspecies P. agapetillus, very small, and of P. intermedius, moderately large. Distinct from it and widely separated is a larger species apparently closely allied to P. turgidus.

There is a most remarkable similarity between the Recent hares and rabbits, and their ancestors in the Oligocene. They evidently became adapted early to an

environment which, relative to its great diversity, has changed but little in the long lapse of time. Since their habitat and habits have been identified with swamps, plains, mountains-in fact, every conceivable condition -no barriers seem to check them; and because of their wide freedom and constant intermixing, they have changed but little since the time of Palæolagus in the Oligocene.

Generic characters.-As early as 1869 Joseph Leidy1 drew attention to the distinction between the Recent and Oligocene forms as shown by the three and two lobes of 1 J. Leidy, Journ. Acad. Nat. Sci. Phila. (2), 7, 331-334.

P3. Cope,2 Forsyth-Major,3 Matthew, and others have since pointed out additional differences: Palæolagus shows well developed postfrontal processes, the basicranial angle very small, the brain relatively small and flat, a less deep infolding of enamel on the internal side of the upper molars, and the presence of a crescentic lake. In all the Oligocene species the permanent lower teeth, when little worn, show a small third lobe arising on the posterior side of the second lobe near its summit; this, however, soon disappears. It is an interesting fact that the two lobes of the lower teeth are sometimes united only by cement, having no enamel connection whatever (fig. 20).

3

In the young, the anterior lobe of P, is a distinct, nearly isolated cone, but later the indentations, especially that

FIG. 2.-Palæolagus haydeni. Cat. No. 10304, Y. P. M. Palatal view of skull, to show small posterior nares, Pn, and anterior palatine foramina, Apf. Nat. size.

on the inner side, disappear, leaving the tooth as a single column with a shallow groove down the outer side. The anterior lobes take on two distinct types in the specimens at hand, i. e., that of a cylinder, round, or flattened and oval in cross-section.

Forsyth-Major has pointed out that the anterior teeth, both above and below, are more complicated than those posterior; this, he says, is due to the loss of the first and second molars of ancestral forms, thus throwing the additional burden on the anterior, terminal members of the series. It is characteristic of the genus Palæolagus that the posterior lobe of each lower tooth, after P3, should be smaller than the anterior one.

Additional features.-In comparing the fossil and Recent skulls (see figs. 1-3) of the family Leporida in the Marsh Collection, the following points have been noted.

2 E. D. Cope, Rept. U. S. Geol. Survey Terr., 3, 870, 888, 1884.

C. J. Forsyth-Major, Trans. Linn. Soc. London (2), 7, 463-487, 1899.

W. D. Matthew, Bull. Am. Mus. Nat. Hist., vol. 16, 306-308, 1902.

Palæolagus.

Palatine fissure opposite P2.
Palatine fissure very narrow.
Posterior nares very narrow.
Posterior nares opposite M2.
Palatal length ant.-post. 8 mm.
Upper tooth series with curved
outer border due to small P2
M3.

Lepus.

Same position.

Very wide.
Very wide.
Opposite P1.

5 mm. on a much larger skull. Series with straight outer border.

P3 narrow anterior and M2 nar- P2.3 wide teeth, also M2. row posterior.

M, grooved on both sides.

M, grooved exterior.

Angle of ramus with narrow ex- Angle very wide ant.-post. tension.

Body of ramus deeper and Body of ramus slender.

wider.

Incisors begin under M, in thick- Incisors begin anterior to P.

ened ramus.

Diastema relatively short.
Anterior to malar, no pit.

On outer side, a fossa.

Diastema long.

Malar with foramen.

On outer side, sometimes a foramen.

Pn

Apf

FIG. 3.-Lepus. Cat. No. 01370, Y. P. M. Diagram of palatal view of skull. Posterior nares, Pn; anterior palatine foramina, Apf. Nat. size.

Other seemingly important features which have come out in the course of this study are: the presence of a coronoid process on the jaw; the straight, much narrower ilium; the acetabular notch (which becomes a foramen in the hare); the thin, erect tubercle just in front of the acetabulum for the origin of the rectus femoris (later becomes flattened and oval in outline); the narrow head of the femur (contrasted to the broad one in Lepus, with the larger trochanters and the additional sharp edge extending distally), and the more prominent but more simple and restricted minor trochanter; all are to be seen in Palæolagus.