The characters displayed by the second cranium lead me to suspect that it is that of a female. A striking feature of the superior dental series is the small size of the canine, which is also not much compressed at the base. As regards the cranium, the sagittal crest is only distinct over the posterior part of the brain case; the zygomata are not very widely expanded, and the muzzle is narrowed. The external infraorbital foramen is large.

The mental border of the mandibular ramus is not flared downwards but is continuous, but the external is separated from the anterior and inferior faces by strong angles. The diastema is long. Three molars, all large; the first without anterior basal tubercle, the second with a large one. Sectorial tooth the longest, with well developed simple cutting heel.

This sabre-toothed tiger is larger than the Machærodus primærus, and is more like the animal indicated by a fragment of the lower jaw named by Leidy, M. occidentalis. But the latter agrees with the M. primacus in the relatively small size of teeth, especially of the first premolar, and in their oblique position, characters not seen in M. brachyops.

PERISSODACTYLA.

ANCHITHERIUM EQUICEPS, sp. nov.

This animal is represented by a portion of the skeleton including a complete cranium of one individual with mandibular rami of several others. The characters of the species are well marked, and do not approach very nearly to those of any other known to me.

The skull is considerably larger than that of A. bairdi, and the length PROC. AMER. PHILOS. SOC. XVIII. 102. J. PRINTED DEC. 30, 1878.

is greater as compared to the transverse and vertical diameters. The preorbital region is but little concave, and the anterior border of the orbit is above the posterior half of the first true molar. The molar teeth present a tubercle between the anterior lobes, and a weak cingulum extends round the inner base of the anterior one, and in the second premolar, round the base of both inner lobes. Thence it passes round the anterior base of the crown and ceases in a tubercle which rises in contact with the anterior median crest. On the posterior side of the crown the cingulum in like manner terminates in the large three-sided posterior marginal tubercle. The anterior median tubercle-crest is well distinguished from the anterior inner tubercle and is directed very obliquely. The posterior median crest is continuous with the inner, and is well separated from the external crests. The external basal cingulum is robust, the columns are prominent, and the outer faces of the external crescents deeply impressed but with a well marked median ridge. The external cingulum and its margins is rugose; other parts of the enamel smooth. The first premolar has two roots; the second premolar is as long as the fourth, and longer than the last true molar.

From A. condoni Leidy, this species differs materially in the composition of the superior molars. In that species there are no inner tubercle and cingulum; the anterior median crest is more completely separated; the anterior cingulum does not cease with the anterior marginal tubercle, and the posterior marginal tubercle is linear, not trihedral.

ANCHITHERIUM BRACHYLOPHUM, sp. nov.

Portions of the maxillary bones supporting molar teeth, indicate a species of the size of the A. equiceps, but differing in various respects.

The median and inner tubercles are not deeply separated, and the former are cut off from the external crescents by a deep fissure. There is no tubercle between the bases of the inner cones, nor is there any internal cingulum. The anterior cingulum does not develop a distinct tubercle, and does not extend to the anterior extremity of the anterior outer crescent. The posterior cingulum develops a large trihedral tubercle, and then extends nearly to the external crescent. The external cingulum is

robust, and the external columns are prominent; the intervening spaces are impressed, and have a distinct median ridge. Enamel smooth or slightly rugose at base of crown.

Measurements.

M.

Length of two superior molars....

.030

Diameter of first superior molar-
f antero-posterior.

.015

transverse.

.017

These dimensions are those of the A. equiceps.

ANCHITHERIUM LONGICRISTIs, sp. nov.

This is a smaller species than the two above described, having the dimensions of the A. bairdi. The best specimen representing it consists of a right maxillary bone, which supports all the molars excepting the last. The infraorbital foramen issues above the third premolar. The first premolar is two-rooted; the second is not elongate, and is equal to the other premolars, or the penultimate true molar, in antero posterior diameter. There are no interior basal tubercles or cingula, but the anterior cingulum has a tubercle which is appressed closely to the anterior median. The posterior cingulum expands into a large trihedral posterior marginal tubercle. The anterior median tubercle crest, appears in the worn state to be moderately distinct from the internal; both it and the posterior middle are characterized by their production outwards; the latter passing between the exterior crescents and forming a junction with their common connection. The external cingula are not strongly marked, nor the external faces of the crescents impressed; the latter are convex, and with the median ridge little distinct. Enamel smooth.

In the Annual Report of the U. S. Geol. Surv. Terrs. for 1873,* I gave the comparative characters of the three species of this genus then known to me, viz.: A. bairdi Leidy; A. cuneatum Cope, and A. exoletum Cope. I now give a table in which the three species above described are introduced, with the A. condoni Leidy.

AA tubercle between the internal lobes of the superior molars. Larger; median tubercles well separated; large anterior and posterior marginal tubercles....

A. quiceps. Smaller; median tubercles not separated; no anterior marginal ard a small posterior marginal tubercle. ...

AA No tubercle between inner lobes.

Page 496.

A. bairdi.

Cope.]

i. External cingulum robust.

Anterior median crest little or not distinct.

[Nov. 15.

Larger; median crests cut off externally; no anterior marginal tubercle; external faces impressed.... ..A. brachylophum. Small; posterior median crest confluent with external crests; an anterior marginal tubercle; external face little impressed..................A. longicristis. BB Anterior median crest isolated.

Larger; a large anterior marginal tubercle; posterior marginal linear wrinkled. .A. condoni.

Small; anterior marginal tubercle minute, posterior triangular; median crests short; smooth..... A. cuneatum.

ii. External cingulum narrow.

External faces without median rib; median crests short, the anterior cut off; marginal tubercles small...

STYLONUS SEVERSUS, gen. et sp. nov.

.A. exoletum.

Gen. Char. These are derived from superior molar teeth Stylonus is allied to Hippotherium in details, including the isolation of the anterior internal enamel covered column, which thus forms an island of dentine, and in the prismatic character of the tooth. It differs from it in the fact that the posterior internal column is isolated in the same manner as the anterior, thus forming a second island on the triturating surface of the crown. This interesting new genus adds one to the already numerous forms of extinct equine animals. It carries to its limit the line of development which retains the inner tubercles of the molar crown distinct from the median. The preceding station on this line which we know is the genus Anchippus, where the median crests have not assumed the antero-posterior direction belonging to the higher equine genera, and where the molars have short crowns and long roots. We may then believe that the line which includes Anchippus, Hippotherium, and Stylonus, is a side branch from that which terminated in Equus. The line of Equus must be traced from Anchitherium through Protohippus and Hippidium.

Specif. Char. Two superior molar teeth were accompanied by a number of inferior molars as having been all found together, but whether they belong to one individual is uncertain. The dentinal lakes of the superior molar are confluent by the median transverse valley, and increased wear would probably join the posterior pair by their posterior angles. The borders of the cementum lakes are simple, except one or two plications on their opposed adjacent borders, and one at the posterior inner part of the posterior. The internal columns are small, and their sections form two equal ovals with their long axes antero-posterior. The anterior dentinal lake sends off a narrow loop towards the posterior part of the anterior column. The shaft of the tooth is incurved, and the external face is unequally divided by the usual ridge. The wide gutters on each side of the latter are uniformly concave, and contain a rather shallow deposit of

cementum.

1878.]

[Cope.

In the inferior molars the two median interior tubercles are stout, and the loops which they bound, are nearly enclosed. There is a tubercle between the bases of the external columns.

.005

Long diameter internal column-lake..

From the Pliocene formation of Cottonwood, Grant co., Oregon.

DEODON SHOSHONENSIS, gen. et sp. nov.

Gen. Char. These are indicated by the terminal portion of the lower jaw of a huge mammal, which does not resemble that of any known genus of this order. It supports on the side, three incisors, one canine, and two premolars, which form an uninterrupted series. The first premolar has two roots; and the canine is of huge proportions. The mandibular symphysis is coössified, and there are no osseous tuberosities on it nor on the adjacent parts of the rami.

The characters of the piece on which this genus is established indicate that the latter probably pertains to the Chalicotheriida along with Menodus and Symborodon. From these its six inferior incisors distinguish it, while the absence of a diastema separates it from Chalicotherium. From Palaosyops and Limnohyus it may be known by the large two-rooted first premolar, or more correctly, in all probability, by the absence of the first premolar of the inferior series. In the relatively powerful canines it resembles the last named rather than the first named genera.

Specif. Char. The canine teeth are very robust, as in the species of Elotherium. The inferior face of the symphysis is not steeply inclined, and is quite elongate. It is narrowed near the bifurcation and expands to a rounded incisive border. The first incisor is narrower than the second and third, which are robust. There are two small mental foramina, the larger below the anterior root of the anterior premolar; the second below the anterior root of the second premolar.

Measurements.

Length of symphysis above.....

Width between bases of canines..

M.

.155

.100

.055

second incisor..... .022

Antero-posterior diameter of base of canine....
Transverse

Diameter of base of first premolar antero-posterior.... .040

transverse......... .025

This species is the largest of the North American Perissodactyla, with the possible exception of the Menodus proutii.

ARTIODACTYLA.

HYOPOTAMUS GUYOTIANUS, sp. nov.

This species of a genus little known in North America, is represented by