Part 4

It is probable that the fore-shoulders were of the same height. From the atlas, axis, and from other cervicals, several dorso-lumbar vertebræ, and part of the sacrum, a rude estimate places the length of the animal at sixty-seven inches, or nearly six feet, including the head, and excluding the tail.

In general features it strongly resembled the tapir, with stout body, slender tail, and very short neck, compensated by a proboscis of considerable length. In comparing the heads of the ancient and modern representatives of this class of Perissodactyles, the points of contrast are the wide stout zygomas, the deep temporal fossæ, the protruding nasals, and the narrow gaps in the dental series of the older type.

There are also strong points of resemblance in the structure of the _Palæosyops_ and _Palæothere_. Some of the cranial homologues have been detailed by Dr. Leidy. The femur of the Palæothere is shorter, the tibia longer; they are both much stouter. The tarsus of the _Palæosyops_ is narrower, while the remainder of the Pes is very similar. The pelvis, and particularly the ilium and acetabulum of _Palæosyops_, is more palæotheroid than tapiroid. The similarity of the fore-shoulder in the two types is also striking. The neck of the _Palæosyops_ was probably shorter.

In the descending series of _Palæotheres_ terminating in the diminutive _P. minus_, and characteristic of the upper eocene of France, we have an interesting counterpart in the large family of _Palæosyops_, of equal diversity of size and characteristic of our lower eocene, and it is hoped that future discoveries will render a complete discussion of this interesting coincidence possible.

LIMNOHYUS, Leidy.

Proceedings Academy Natural Sciences, Phil., 1872, p. 242; _Palæosyops_; Marsh, American Journal Sci. and Arts, 1872, p. 122; Hayden's Survey, 1872, p. 592, Cope.

_Generic characters._--Resembles _Palæosyops_ in general features. Distinction founded on the possession of two conic tubercles, of the inner series, on the last superior molar instead of one.

Limnohyus laticeps, Marsh.

_Palæosyops Laticeps._ Am. Journ. of Sc. v. iv. p. 122.

_Specific characters._--"Cranium is broad. The zygomatic arches much expanded. The nasals are narrow and elongated, and more like the corresponding bones in Hyrax than those in the larger pachyderms."

Fragments of the upper molar and premolar series. The species is determined by measurements given by Dr. Leidy of the second upper molar.

LEUROCEPHALUS, _Gen. Nov._

Established on a specimen having a nearly complete dentition, and portions of the cranium.

Dental Formula: (I. 3/3, C. 1/1, Pm. 4/4, M. 3/3,) × 2 = 44.

Upper incisors acute, with strong posterior ridges, lower incisors compressed and laniariform, canines compressed, with serrated cutting edges; first upper premolar with rudimentary anterior lobe, last upper molar with rudimentary postero-internal cusp. Molars constructed as in _Palæosyops_, but higher, with sharper cones and more erect external lobes. Internal median valley very much deeper. Little or no depression at the forehead; zygomatic arch round, comparatively straight and does not project outwards, and with obscure postorbital process. Premaxillaries short and straight. Mandible with nearly straight lower margin, and shallow masseteric fossa; mental foramen single.

Leurocephalus cultridens, _Sp. Nov._

This species was considerably larger than _Palæosyops major_, with which it shows affinities, as also with _Titanotherium Proutii_. See Plate IV.

The _Frontal_ is narrow and flat, or slightly arched. It sends out a strong curved postorbital process, which projects outwards, but not so much outwards as in _Palæosyops_. The sagittal crest runs back from the postorbital in a low rounded ridge, rising but little as it recedes. The superciliary ridge is distinct, and is pierced by two small venous foramina. The shape of the entire bone is much as we find it in the dog, except that it does not arch so much. One of the most marked differences between this genus and _Palæosyops_ is here shown. In the latter the forehead rises abruptly from behind the orbit, while in the former there is only a slight rise for some distance behind the orbit. As the bone is broken here, it is impossible to state whether there is any rise at all. Probably not, however. Below the postorbital process, on the lateral aspect of the bone, there is a low ridge which separates the orbit from the temporal fossa. The under surface of the frontal is smooth.

The _Nasal_, of which but a small portion is preserved, is flat on top, but bends downward at the angle.

The _Maxillary_ is long and stout, over the last and penultimate molars it broadens to form the floor of the orbit, which is of unusual size. Between the canine and the malar the maxillary arches inwards, forming a perceptible concavity, at this point it reaches its greatest vertical height, as it rises to join the nasal. The alveolar border is curved in two directions, one with the convexity outwards, and the other downwards. It exhibits no emargination in the diastema between the canines and molars. The palatine plate is long, thick, and narrow; it is flat fore-and-aft, but concave transversely, owing to the elevation of the alveolus; the suture also is raised slightly. In thickness it varies; being thickest between the canine and the second premolar, and beyond this becoming thinner. Its forward termination seems to be obtuse, running for a short distance along the premaxillaries. The infraorbital foramen is large, situated over the fourth premolar, lower down, and nearer to the malar than in _Palæosyops_.

The _Premaxillary_ is rather short and stout; it is slightly compressed, and ends in a sharp keel on top. Although not so thick as in _Palæosyops_, it is much larger vertically. The inner surface is ridged; it has no palatine process, and no spine, so that the incisive foramen is large and undivided. There was no symphysis between the two premaxillaries, they do not show even any articular faces for each other, so that they may not have been in contact during life. The animal was adult, but not old. The incisive alveolus is short and straight, and is but little out of the line of the molars. There is a very long diastema between the incisors and the canine, and here the premaxillary is deeply notched to allow the passage of the lower canine.

The _Malar_ is very different in shape and size from the same bone in _Palæosyops_. Its facial extent is greater, as it articulates with the maxillary as far forward as the first molar. It is not so broad from above downwards, but is considerably thicker; the articulation with the squamosal is by flat surfaces. The postorbital process is small and indistinct. The orbit is of great size; its breadth, shown by the maxillary floor is unusual, but its fore-and-aft diameter is extreme, being nearly twice as great as in a large _Palæosyops major_.

The _Squamosal_ is a short, slender, and trihedral bone; it is not at all like the squamosal of _Palæosyops_. It is smaller even than that of _P. paludosus_; its outer margin is not turned up, making the upper surface concave; it does not project much outward, and scarcely at all downwards, as this is rendered unnecessary by the flatness of the forehead. The chief difference, in the size of this bone, between this genus and _Palæosyops_ is found in the much greater vertical and lateral diameter of the latter; in length they are about equal. The glenoid cavity is large, shallow, and transverse.

As a whole, the zygomatic arch is comparatively slender; it is rounded, and does not project much laterally from the side of the head; but its chief peculiarity consists in the fact that it is nearly horizontal. It is thus altogether different from the arch of _Palæosyops_.

The _Occipital Condyles_ are different from those of that genus. They are flatter, shorter from above downwards, and proportionately much smaller; but are expanded laterally in much the same manner. At the border of the foramen magnum they are gently rounded instead of having a sharp angle. These borders are segments of circles, but as the condyles are broken from the rest of the occiput, we cannot infer from this the shape of the foramen.

The _Mandible_ is long, stout, but comparatively shallow. It is of nearly uniform thickness throughout, and does not exhibit the thickening of the alveolus and thinning, of the lower margin, which is shown in _Palæosyops_, especially in _P. major_; and the downward and inward arching of the alveolar border is not marked to the same extent as in that species. The lower border is nearly straight, and has but one slight emargination just behind the symphysis. The ascending portion of the ramus rises near the last molar quite abruptly, and makes an angle of nearly 90° with the horizontal portion. The masseteric fossa is shallow and obscure, and the anterior bounding ridge is almost obsolete. This part of the jaw is very different from any of the species of _Palæosyops_. The symphysis is quite long, and extends back as far as the second premolar; the chin is probably rounded. The dental foramen is situated high up in the ascending portion of the ramus; the mental foramen is placed below the second premolar; it is large and single.

_Cranial Measurements._

M. Breadth of frontal at postorbital process ·045 Breadth of frontal in front of postorbital ·030 Breadth of nasal just in front of orbit ·032 Length from angle of nares to end of premaxillary ·1235 Length of premaxillary ·056 Length of maxillary ·230 Breadth of palatine process at canine ·026 Breadth of palatine process at second premolar ·029 Vertical height of maxillary at angle of nares ·064 Breadth of maxillary across floor of orbit ·058 Fore-and-aft diameter of orbit ·054 Length of malar along maxillary ·094 Vertical diameter of malar behind maxillary ·029 Transverse diameter of malar behind maxillary ·033 Fore-and-aft diameter of glenoid cavity (about) ·029 Vertical diameter of squamosal at end of malar articulation ·032 Transverse diameter of squamosal at end of malar articulation ·0325 Length of ramus mandibuli from symphysis to ascending portion ·177 Depth of jaw at last molar ·068 Depth of jaw at second premolar ·061

DENTITION.

Upper Jaw.--The incisors, three in number, are placed close together in a nearly straight line, which does not make so great an angle with the line of molars as in _Palæosyops_. They increase regularly in size from the first to the third, which is very large. They all have stout rounded fangs, and sharp pyramidal crowns, with strong basal ridges separated from the acute blades by deep clefts. Between the incisors and the canine there is a long diastema.

The _canine_ is of great size; it has a swollen fang, and a long recurved crown which is much compressed, and has sharp serrated cutting-edges. The external face is the more convex, the internal has a well-marked basal ridge, and both are longitudinally striated. The canine is separated from the premolars by a short diastema.

_Premolars._--The first premolar stands by itself, separated by a short interval from the second. It is implanted by two fangs, and has a compressed crown with sharp cutting-edges. It is nearly twice the size of the corresponding tooth in _Palæosyops_, which is simple and conical. In the specimen under description there is, besides the principal lobe of the tooth, a rudimentary anterior lobe which gives the crown an elongate shape. The basal ridge is shown on the inner side only. The second premolar has a crown which is oval in section. The external part consists of two sharp-pointed cusps, separated by a valley, but confluent at base; while the internal division is a low ridge (not a pointed cone as in _Palæosyops_) with a tubercle developed behind it. The basal ridge is marked all around, and sends up a buttress along the antero-external lobe; as is also the case in the third and fourth premolars. These are enlarged copies of the second; but have the internal lobe elevated into a sharp cone, and showing a much stronger basal ridge and deeper median valley. These teeth differ in several respects from the premolars of _Palæosyops_. The crowns are higher and the lobes sharper; the basal ridge is more distinct, and is not interrupted at the internal cusp; the external ascending buttress is stronger; and there is no fold between the external lobes of the fourth.

The molars are constructed in a manner which resembles that of _P. paludosus_ rather than of _P. major_, but its resemblance to the form shown in _Titanotherium_ is stronger than to either. They have broad, square crowns, which increase progressively in size from first to last. There is a convexity running up the median line of the external lobes, and the two posterior lobes are connected together at their bases. The first molar does not exhibit such a decided increase in size over the last premolar as is seen in _Palæosyops_; the two external lobes are more erect and sharper than in any form of that genus. The cingulum is complete even across the internal cones, and the median valley is very deep, as in _Titanotherium_. There is a conspicuous fold at the junction of the external lobes, and a minute tubercle between the two anterior lobes; this tubercle is present only in the first molar, and not throughout the series, as in _Palæosyops_. The second molar in general form is like the first; but is larger, has a deeper median valley, more conspicuous external folds, and a stronger basal ridge. There is also some change in the proportions of the crown; the first measuring the same in both directions, while the second is wider than it is long. The last molar has but one internal cone; the second is represented by a tubercle; which however is a true rudimentary lobe and not a development of the basal ridge. In this tooth, the external fold is very large and the median valley very deep.

Lower Jaw.--The lower molars and premolars are very much like those of _Palæosyops_, but are longer, narrower, and higher. The incisors are not at all like _Palæosyops_, but are compressed and laniariform, with acute crowns and sharp cutting-edges. The canine is not present in our specimen; but that it was large, is shown by the long diastema between the upper canine and incisors.

_Premolars._--The first is small, simple, and implanted by a single fang close to the canine. The diastema between it and the second premolar is about one half of that in _P. major_. The second premolar is the most peculiar tooth in the lower series; as it carries the development of the anterior lobe at the expense of the posterior lobe, to a still greater extent than in _Palæosyops_., forming a crown like the blade of the carnivorous sectorial. The third lobe of the last molar is no longer a simple cone, but a functional lobe, with two crests running from it, which bound a median valley.

_Teeth Measurements._

UPPER JAW. M. Length of entire dental series ·275 Length of incisor series ·375 Length of diastema between canine and incisors ·018 Fore-and-aft diameter of canine ·019 Transverse diameter of canine ·015 Length of diastema between canine and premolars ·0145 Length of premolar series ·083 Length of first premolar ·016 Width of first premolar ·009 Length of second premolar ·021 Width of second premolar ·017 Length of third premolar ·022 Width of third premolar ·022 Length of fourth premolar ·024 Width of fourth premolar ·027 Length of true molar series ·106 Length of first molar ·031 Width of first molar ·031 Length of second molar ·037 Width of second molar ·040 Length of third molar ·038 Width of third molar ·041

LOWER JAW. M. Length of entire molar series ·202 Length of premolar series ·081 Length of true molar series ·121 Length of second premolar ·024 Width of second premolar ·0125 Length of third premolar ·022 Width of third premolar ·014 Length of fourth premolar ·0235 Width of fourth premolar ·0155 Length of first molar ·030 Width of first molar ·017 Length of second molar ·038 Width of second molar ·021 Length of third molar ·053 Width of third molar ·024

Found at Henry's Fork Divide.

This may eventually prove to be a species of _Telmatherium_, (Marsh); but the description given by him of that genus is so brief and uncharacteristic that it might apply to any of the allied genera. Indeed, Dr. Leidy has regarded it as a synonym of _Palæosyops_.

HYRACHYUS, Leidy.

Proc. Ac. Nat. Sc., 1871, p. 229, _et seq_.

A genus of tapiroid mammals, which is thus defined: "_Lower Jaw:_ Third molar with two crests; four premolars, third and fourth with one transverse and one longitudinal crest. _Upper Jaw:_ Seven molars, first without interior heel; premolars with two transverse crests." (Cope.)

_Synopsis of Species._

I. Long diastema between lower canines and molars. A. Lower jaw with six molars _H. nanus_. B. Lower jaw with seven molars. _a a._ Upper molars with complete cingulum. Enamel wrinkled. _a._ The last molar with two external lobes on nearly the same transverse line _H. intermedius_. _b._ Last molar with the external lobes on the same longitudinal line _H. modestus_. _b b._ Upper molars with cingulum incomplete externally. _a._ With anterior conical buttress larger than anterior lobe. α. Buttress separate, and no fold from anterior lobe _H. princeps_. β. Buttress united, and quite large fold from anterior lobe _H. imperialis_.

_b._ With anterior conical buttress smaller than anterior lobe. α. Tooth large _H. eximius_. β. Tooth smaller _H. agrarius_.

_c c._ Cingulum only on outer side of first molar, buttress separated by a ridge from anterior lobe, fold from this lobe very prominent. _H. implicatus_.

II. Short diastema between lower canines and molars.

A. Descending ridge from antero-external point of lower molar extends entirely across the crown of the tooth anteriorly _H. crassidens_.

Hyrachyus imperialis, _sp. nov._

Established on the second and third molars of each upper jaw, and three premolars, and one lower molar, portions of the skull and vertebræ.

This species is, with the exception of _H. princeps_, (Marsh), the largest species of the genus as yet known. It differs from _H. princeps_ in the greater proportionate length of the molars, in their larger size, compared with the bulk of the animal, and in the less separation of the anterior external conical buttress. The third molar is the largest; the fold extending from the antero-external lobe into the valley is very conspicuous. The basal ridge (which is very strongly marked on the posterior edge), is very feebly indicated on the exterior. The transverse crests are more oblique in the second than in the third, but in the latter the valley is deeper and the crests slightly longer. The anterior conical buttress is of great size, being larger than the anterior lobe. The premolars have, as usual, one internal cone; the anterior and posterior external lobes approach close together, while the accessory fold from the anterior lobe becomes very prominent, reaching the internal cone and enclosing a valley between itself and the transverse crest. The basal ridge does not extend around the inner part of the crown as in _H. agrarius_.

The only lower molar we have, seems to be a penultimate molar of the right side. The basal ridge is large anteriorly, very short posteriorly, but does not appear at all upon the sides, as in _H. agrarius_.

The remaining bones of the skeleton indicate a rather small animal, the teeth are therefore proportionately very large.

The occipital condyles are small and sessile; they are much extended laterally, and the external angles are pointed. In other respects they resemble the condyles of _Palæosyops_. The zygomatic arch is slender and does not curve outward strongly. We cannot tell how far the malar encroaches upon the face. After leaving the maxillary it becomes much compressed; it has no postorbital process. The maxillary is of unusual breadth, extends far backwards, and it forms the floor of the large orbit. The mandible is slender and compressed, with a large dental canal.

The atlas is small, and has narrow transverse processes, which are perforated by a large vertebraterial canal. The dorsals have considerably depressed centra, and the ribs are slender.

_Measurements._

M. Length of last molar ·025 Breadth of last molar ·030 Length of second molar ·024 Width of second molar ·0305 Length of last (?) premolar .018 Width of last premolar ·0245 Length of second lower molar ·025 Width of second lower molar ·018

From Henry's Fork Divide.

Hyrachyus intermedius, _Sp. nov._

Established on the upper true molar series of the right side.