The skull of the type (No. 110) of this species has been described under Section III, page 96. The dentition is that of a young individual, and is beautifully preserved. Both of the rudimentary second upper molars were procured, but one of them was unfortunately lost. No other remains were found. All the characters of the skull and teeth are brought out in the lithographic plate. The animal was one-fourth larger than the American Puma (Felis concolor), and slightly larger than either of the specimens referred to Palæonictis gigantea by De Blainville and Gaudry. As in F. concolor the lower incisors are of nearly equal size; while the upper increase rapidly outwards, the first being very small and the third being large and caniniform. The canines are large, vertically striated and recurved; they exhibit an internal ridge extending from the posterior base to the apex.

Lower Series.-The first lower premolar is low and obtuse with a distinct talon. The second has a pointed protocone, a more elevated talon, and a faint external cingulum. The third has a higher protocone, a prominent basal cusp, and distinct external and internal cingula. The fourth premolar is tricuspid, and exhibits a cusp analogous to the paracone (tetartocone, Scott); also the more elevated basal cusp, rising from the talon and analogous to the hypoconid (=deuteroconid, Scott). The cingulum completely encircles the crown, except at the ends, and upon the inner side of the talon is marked by a little tubercle. The first true molar is a fine example of the typical "tuberculo-sectorial" type. The elevated trigonid supports the lofty protoconid and subequal para- and metaconids, while the talon supports three subequal cusps, the hypoconid, the hypoconulid or posterior intermediate cusp, and the entoconid. The second molar is of much smaller size; the trigon bears a reduced metaconid, while the talon is still more reduced by the loss of the two internal cusps, the hypoconid alone persisting.

Upper Series.-The first upper premolar is small and single fanged, with a minute basal cusp. The second has quite a prominent basal cusp with a faint external and an internal cingulum shelf. The third premolar has almost a blade or shear formed by the protocone and deuterocone or basal cusp, and a crenate cingulum shelf. The fourth premolar is, we believe, the incipient sectorial; it has the three external cusps which compose the upper sectorial of Felis, but the middle cusp, or protocone, is much the most prominent; this with the posterior cusp (deuterocone) forms a sharp-edged shear, against which abuts the shear formed by the paraconid and metaconid of the first lower molar. Herein lies a close resemblance to the relations of these two teeth in the Felidæ, and these molars furnish a simple key to the feline sectorials, as shown in the accompanying diagrams. (Fig. 7.)

The transformation of the feline upper premolar has taken place by the subequal development, A, B, of the three external cusps, te, pr, and de, and by the shifting forward of the internal

de

te..

A

pad

te

Ar

de

B

met

pad

jird

Fig. 7: The homologies of the Molar Cusps in the Felidæ. A, Palæonictis occidentalis. B, Felis concolor. de, deuterocone. tr, trittocone. te, tetartocone. Last upper premolar and first lower molar in opposition.

cusp tr. Meanwhile the lower molar has lost the entire talon (hyd, hľa, eno) and the metaconid (me) is reduced to a rudimentary stage in which it is barely perceptible. This conforms with the description of this transformation given. by Cope,' but adds a more exact statement of the homologies of the cusps. The degeneration of the metaconid ist well shown in the series of sectorials exhibited in Fig. 5.

The reduced condition of the upper true molars of Palæonictis is most remarkable in an animal of such an early period as the Wahsatch. The third molar has disappeared entirely, the second has been reduced to an extremely small rounded tooth; the first molar is already smaller than the fourth premolar. The pattern of the first upper molar is somewhat similar to that of Oxyæna, but the protocone is directly internal instead of being pushed forwards; the external cusps, paracone and metacone, are subequal and slightly compressed; on the trigon between these high cusps and the low protocone are small intermediate tubercles, pl. and ml. There is a prominent cingulum and a posterior basal

cusp.

Ambloctonus sinosus Cope.

The skull of Palæonictis renders a great indirect service in enabling us to clear up the structure of the enigmatical Ambloctonus. This was established upon a much fractured maxilla and mandible, by which Cope was wholly misled as to the notation and homologies of the teeth and the relationships of the genus, although in the 'Tertiary Vertebrata' he placed it near Palæo

The mechanical causes of the development of the Hard Parts of the Mammalia. Journal of Morphology, Vol. III, 1889, p. 232.

nictis. Schlosser has rightly discerned the resemblance between these forms.

The accompanying figure presents our interpretation of this fractured type. There are two lower molars and but a single upper molar; the maxilla turns sharply in behind the first molar,

Fig. 8. Ambloctonus sinosus, type specimen, National Museum. This drawing is a composition of the left mandible and right maxilla of the same individual. Three-fifths natural

size.

and leaves no doubt as to the absence of both the second and third upper molars. The gap between the fourth premolar and first molar does not contain an extra tooth, as Cope supposed. The tooth Cope mistook for the first molar is really the fourth premolar; the gap in the jaw closes up when the matrix is removed. The superior formula was therefore undoubtedly p=4,

This interpretation is supported by the structure of the lower molars, ie, by the marked degeneration of the talon of m2 which it is obvious has nothing to abut against in the upper jaw. Two stages in the reduction of this talon are shown in Fig. 5; in the type specimen D, there is no talon; in a second specimen, rightly associated with the genus by Cope (see Fig. 5, E), there is a rudimentary talon, t.

Family OXYÆNIDE Cope.

This family is represented in the collection by eight specimens belonging to the two well-known Wahsatch species, O. lupina and O. forcipata.

Genus Oxyæna Cope.

They enable us to add several important family and generic characters. Cope has defined the genus as probably possessing no inferior incisors. (1) We find that there are three incisors in both the upper and lower jaws, as in Palæonictis. (2) A tarsus of P. forcipata in the collection does not support Cope's view that there was a cleft between the third and fourth digits. (3) There is an os-centrale in the carpus. (4) The lumbar vertebræ have involuted zygapophyses. (5) The femur has a faint rugosity representing the third trochanter.

Oxyæna lupina Cope.

We have referred to this species portions of three lower jaws (Nos. 102, 103, 104), and a fragmentary lower molar (No. 105); also the fairly complete skeleton and teeth of a single individual (No. 107).

The Manus of Oxyana.-As noted by Cope, the skeleton of Oxyana is much smaller and lighter in proportion to the skull than in the Carnivora.

The scaphoid rests upon the trapezium, trapezoid (which is the only carpal missing), and centrale. It is entirely distinct from the lunar. The lunar rests inferiorly, by nearly subequal facets, upon the centrale and unciform, with a narrow anterior and broad posterior contact with the magnum. The cuneiform rests upon the oblique outer surface of the unciform. The trapezium is depressed so as to form a lateral internal support for the second digit. The magnum presents a subquadrate anterior outline. The unciform has an internal contact with the middle digit, and an oblique external facet for the fifth. The metapodials are much shorter, more spreading, and less firmly interlocking than in the Felidæ,

Skeleton of the Limbs and Arches.-The humerus has a very

prominent deltoid ridge, and an entepicondylar foramen; the trochlea presents, anteriorly, subequal faces for the radius and ulna. The ulna presents, distally, two facets-one for the radius, the other for the cuneiform. The femur presents a pit for the round ligament, a prominent lesser trochanter, and a slight rugosity representing the third.

The lower jaw presents a broad thin angle, and a sharp narrow coronoid process. The roller of the condyle tapers sharply, as in Felis.

Oxyæna forcipata Cope.

We have referred to this species portions of two skeletons (Nos. 108, 109), distinguished by the heavy character of the bones. They include a tarsus, which agrees closely with that referred to this species by Cope, with the exception noted above. The former has two lower teeth associated with it, but they are so broken that the reference is uncertain. A jaw (No. 106), containing fragmentary molars, may also be placed here.

The tarsus (No. 109) is extremely interesting, as it appears to prove that Cope is mistaken in his description of the hind foot of Oxyana. The calcaneum is complete and presents an oval ectal facet and a subcircular sustentacular facet. The astragalus lacks the outer portion of the tibial trochlea; Cope's figure indicates that the tibial facet is very limited in the fore and aft direction, and that therefore Oxyana was a plantigrade; unfortunately this pes does not throw any light upon this point. A very striking feature of the foot is the broad contact between the cuboid and astragalus; the cuboid is, as represented by Cope, directed outwards, but the ectocuneiform is in close contact with it, proving that