PERISSODACTYLA.
Reading edition
ANCHITHERIUM.
Von Meyer, Jahrbuch für Mineralogie, 1844, p. 298.
Anchitherium —— ?
A small calcaneum and astragalus of equine type are provisionally referred to this genus until further material enables us to determine them with certainty.
The astragalus has narrow and very oblique condyles, which are more equal in size than in Orohippus; the neck is very short, the internal condyle reaching to the face for the navicular; the posterior projection of this condyle is much shorter than in that genus. The articular face for the navicular is quadrate in shape and concave; the cuboid face is very narrow. The articulation with the calcaneum is made by a narrow, convex face. When the two are in position the navicular face of the astragalus is in the same horizontal line as the cuboid face of the calcaneum, thus resembling the arrangement of the horse's tarsus rather than that of Orohippus.
The calcaneum is a short, slender bone, having the upper and lower margins convergent toward the tuberosity, and not parallel as in Orohippus. The tuberosity is especially small. The face for the cuboid is very narrow.
From the articular facets of these two bones we can see that the tarsus resembled very much that of the modern horse, with a broad, short navicular, and a narrow cuboid. The strata in which these remains were found were somewhat higher than those containing the bones of Orohippus.
Measurements.
M.
Greatest length of astragalus 0·021
Greatest breadth of ditto ·018
Length of neck of ditto ·005
Width between the condyles ·010
Vertical diameter of face for navicular ·012
Transverse diameter of ditto ·012
Length of calcaneum ·046
Width of face for cuboid ·006
From Henry's Fork.
OROHIPPUS, Marsh.
Am. Jour. Sc. vol iv., p. 207, third series.
Generic Characteristics.—"The crowns of the upper true molars are composed of a pair of external cusps similar to those of anchitherium. There are two corresponding inner tubercles, from which ridges extend obliquely to the anterior inner margin of the outer cusps; but the anterior ridge is divided so as to form an intermediate anterior tubercle. All the teeth preserved have a distinct basal ridge."
Species Known.—
Orohippus pumilus, Marsh. Orohippus major, Marsh. Orohippus agilis, Marsh. Orohippus gracilis, Marsh.
Orohippus pumilus? Marsh.
Specimen obtained. Penultimate and third superior molars, with part of zygoma.
From Cottonwood Creek.
Orohippus major? Marsh.
Femur (Plate IX., Fig. 1).—The femur has a small, nearly hemispherical head, developed on a long and slender neck; the head is but slightly out of the axis of the shaft, and has a large pit for ligamentous insertion. The shaft is long, simple, and curved slightly forward. At the proximal end it is broad and flattened axially; below this it becomes expanded fore-and-aft, but it thickens greatly at the distal end, just above the condyles. The great trochanter is large and retroverted, rising above the head, with two prominences rising from it, one on top, the other back. The digital fossa is wide and deep, penetrating far into the great trochanter. The second trochanter is a small rounded ridge; the third trochanter is large and prominent, curving slightly forward. The condyles are long and narrow, projecting very far back, and are separated by a wide and deep popliteal groove. From the external condyle a low ridge runs obliquely, forming the upper border of the shallow popliteal space. The trochleæ are long, very convex, deeply grooved, and symmetrical.
Measurements of Femur.
M.
Width between head and great trochanter ·019
Width at third trochanter ·034
Diameter of head ·019
Width at condyles ·028
Width of trochlea ·015
Height of great trochanter ·015
Diameter fore-and-aft of shaft at middle ·018
The tibia (Plate IX., Fig. 3) is very long and heavy, with broad proximal articular face, the inner borders of which are prolonged upward and separated by a groove.
The shaft at the tuberosity is subtriangular, with strongly concave sides. The tuberosity is prominent, with a deep pit on its upper surface for the insertion of the ligament of the patella. The shaft below becomes sub-cylindrical, and decreases regularly in size downward. Its curvature is forward. The distal articular face is divided by a smooth ridge into two deep facets. The malleolus is long.
The fibula (Plate IX., Fig. 2) is distinct, straight, and very slender. The distal end is but slightly expanded, and is strongly marked by a vertical groove externally. The proximal end articulates with the overhanging portion of the proximal face of the tibia.
Measurements of Tibia.
TIBIA.
Upper Jaw. M.
Length ·178
Width of proximal surfaces (transverse) ·032
Width of proximal surfaces (antero-posterior) ·019
Transverse diameter of shaft ·022
Antero-posterior diameter of distal articulation ·018
Transverse diameter of distal articulation ·018
The tarsus.—The astragalus (Plate IX., Fig. 5) has the condyles asymmetrical and divided by a deep groove; the head is narrow, with the neck elongate. The face for the cuboid is small, and confined to the external border.
The calcaneum (Plate IX., Fig. 4) is long and compressed, with its upper and lower margins straight and nearly parallel; its tuberosity is large. The face for the cuboid is small.
The navicular (Plate IX., Fig. 6) is proportionately longer and narrower than it is in the modern horse. The internal and middle cuneiforms were probably separate.
Metatarsals (Plate IX., Fig. 7).—Three in number. Are very much shorter proportionately than in the modern horse. In shape they are compressed and arched forward. The distal ends are flattened vertically, arched forward, and deeply grooved in the middle.
The phalanges (Plate IX., Fig. 7) are very short, rather stout, and very smooth and convex above.
The ungual phalanges are very thin and crescent shaped.
Measurements.
ASTRAGALUS.
M.
Greatest width ·029
Greatest length ·022
Length of navicular facet ·017
Width of navicular facet ·012
Length of tibial trochleæ externally ·016
CALCANEUM.
M.
Total length ·058
Total width ·019
Depth in front ·022
Length of heel ·035
Depth of heel ·018
Length of cuboid facet ·014
NAVICULAR.
M.
Width ·009
Length ·010
PHALANGES.
M.
Length of first phalanx ·022
Width of first phalanx ·012
Length of second phalanx ·013
Width of second phalanx ·010
Length of ungual phalanx ·005
Width of ungual phalanx ·010
PALÆOSYOPS, Leidy.
Hayden's Geological Survey of Montana, 1871.—Proceedings Academy Natural Sciences, Philadelphia, 1871, p. 118.—Limnohyus.—Marsh, American Journal Science and Arts, 1872, p. 124.
Generic characters.—The dentition is full, I. 3, C. 1, Pm. 4, M. 3; the same in lower jaw. The internal cones of the superior molars isolated from the crescentoid crests. One inner tubercle on the last three premolars. One internal cone on the last superior molar. In lower jaw, true molars with four acute tubercles alternating in pairs and connected by oblique crests. The last molar adds a fifth posterior tubercle. The last premolar lacks the posterior inner tubercle. The canines are in continuity with the incisors.
A broad, triangular forehead. A wide zygoma. Long, projecting nasals. Large temporal fossæ. High sagittal crest. Prominent and nearly vertical occiput.
Palæosyops major, Leidy.
Survey of Wyoming, 1871, p. 359.—Limnohyus robustus.—Marsh, American Journal Science and Arts, 1872, p. 124.
Specific characters.—Sagittal crest short and thick. Temporal fossæ not very deep. Frontals diverge rapidly. Occipital condyles wide and low; the same is true of the foramen magnum. Meatus auditorius high and deep. Glenoid cavity shallow; no internal process. As compared with P. Paludosus, post-glenoid process not so much compressed. Occipital region comparatively higher and not so concave. The occipital condyles are more prominent. The zygomas are lighter. Head larger than Paludosus, perhaps not so large as Vallidens.
Description from (i) a head, complete, but distorted, with complete dentition, upper and lower. (2) A head somewhat crushed, and lacking some portions, with full set of upper molars and canines. (3) A great number of fragmentary specimens of different parts of the body.
Dentition.—In the upper jaw the incisors are arranged in a semi-circle as in P. paludosus; they have long fangs and short, conical crowns, with a decided basal ridge, which is very strong in the third. They increase from first to third, which is very large and pointed.
The canines have very large and long fangs (longer than the crowns). The crowns are very stout and pointed, constituting formidable weapons. In section they are nearly circular, with a distinct hinder margin and a slight recurve. A rudimentary anterior margin is sometimes present, and of the faces thus marked off, the inner is much smaller and flatter. The general direction is forwards, downwards, and slightly outwards. There is a diastema of about half an inch between the incisors and canines.
Premolars.—The first is very small, about half an inch from the canine, simple and conical, with an obscurely marked basal ridge, and two heavy fangs.
Further description of the upper dentition is unnecessary, owing to the complete work of Dr. Leidy upon the subject.
The lower incisors are placed in a semi-circular row, and are somewhat procumbent, though hardly as much so as in the tapir. They are much as in P. paludosus, but are relatively smaller, and have not such distinct basal ridges; features which indicate a departure from the carnivorous type, and a nearer approach to the herbivorous type. The lateral incisor, though the largest of the series, is not so large nor so pointed as in P. paludosus. There is no diastema.
The canines are about equal in size to those of the upper jaw, growing from stout fangs and permanent pulps. The margins of the crowns are more decided, and are smooth, leaving a very narrow and flat inner face. A feeble basal ridge. When the jaw was closed, the lower canines passed inside and in front of the upper.
The first premolar stands immediately behind the canine, is longer than that of the upper jaw, consisting of a single pointed lobe implanted by one fang, slightly recurved with a flat inner and convex outer face. Passing in front of the first upper premolar, it leaves a considerable diastema between this and the second premolar.
The mandible approximates in form that of the tapir; the lower border is less curved fore and aft, the alveolar border is slightly concave antero-posteriorly. The molars converge in front, presenting a very different arrangement from that in Sus. The ramus is heavy, contracting in depth forward, and very slightly in section. Below the alveolus, on the interior side, the ramus is greatly swollen for two thirds of its depth, to accommodate the very long and strong molar fangs.
The rami converge to the second premolar, where they expand laterally to the canine alveolus. The symphysis is shorter relatively than in P. paludosus, and the chin is regularly rounded in front. The mental foramen is below the second premolar. The dental foramen is small, very high up, and far behind the molars. The alveolar border ascends rapidly behind the last molar, expanding laterally into two ridges.
The coronoid is slender and recurved. The condyle is broad, flat behind, inclines forward internally; there is scarcely any depression between the condyle and the coronoid. The masseteric fossa is very wide and deep. The angle of the ramus is broken, but evidently has no such posterior extension as in P. paludosus. It thins out rapidly behind.
Measurements.
P. pal. P. major.
UPPER JAW. M. M.
Length of entire molar series ·147 ·170
Length of three true molars ·085 ·102
Length of three premolars ·058 ·068
Diameter of last molar, transverse ·039 ·047
Diameter of last molar, antero-posterior ·036 ·036
Diameter of second molar, transverse ·036 ·040
Diameter of second molar, antero-posterior ·033 ·036
Length of incisor series ···· ·075
Fore-and-aft diameter of canine at base ·016 ·021
Length of crown of canine ···· ·033
Diastema between canines and incisors ···· ·013
Diastema between canines and molars ···· ·010
P. pal. P. major.
LOWER JAW. M. M.
Incisor series ···· ·073
Median incisor fang, length ···· ·034
incisor crown, length ···· ·012
Diameter of median incisor crown, transverse ···· ·009
Diameter of lateral incisor crown, transverse ···· ·011
Diameter of lateral incisor crown, antero-posterior ···· ·012
Length of fang of canine ·055 ·052
breadth of fang of canine ·023 ·024
Crown of canine, length ···· ·034
Crown of canine, fore-and-aft diameter at base ·019 ·021
Diameter of first premolar, antero-posterior ·015 ·010
Diameter of first premolar, transverse ·009 ·007
Diastema between first and second premolars ···· ·014
Length of entire molar series ·164 ·186
Length of molar series, omitting first premolar ·132 ·163
Diameter of last molar, antero-posterior ·017 ·050
Diameter of last molar, transverse ···· ·027
Depth of jaw below last molar ·068 ·075
Among other specimens obtained at the divide between Henry's Fork and Cottonwood Creek, was a nearly complete but somewhat shattered skeleton of a Palæosyops major, found contiguous to the head of the same, parts of which are just described. Portions of these are figured on a one fourth scale in Plate II. The description is from a nearly perfect atlas and axis, several cervical, dorsal, and lumbar vertebræ, more or less complete, and a portion of the sacrum and pelvis, in addition to several bones of the limbs.
The atlas has a broad inferior arch, contracted antero-posteriorly, and deeply notched for the prominent odontoid of the axis. The heavy superior arch, inclosing a large and depressed neural canal, is capped by a low tuberosity. It slopes into a flat, and very broad transverse process, which thickens backwards, and is perforated by the vertebraterial canal. Forwards the transverse process is notched for the exit of the first spinal nerve. The anterior or condylar faces are continuous, deeply concave from above downwards; and slightly so from side to side; while the posterior faces are oval, nearly flat, and directed backwards and inwards.
The axis is proportionately small, with a long opisthocœlous centrum, depressed, and produced forwards into a stout conical odontoid process, and marked below by a strong hypapophysial keel, which, developed on the latter half, thickens backwards. The wide and thin pedicles inclose a high neural canal, support the posterior zygapophyses and a prominent and peculiar neural spine. The latter is flattened, broad, and recurved posteriorly, thinning rapidly forwards into a prow-shaped recurved edge. The transverse processes arising from the latter half of the centrum are undersized and widely perforated at base. The anterior faces are very broad, directed outwards, and slightly rounded from above downwards; they expand as they diverge (see Fig. 2). The post-zygapophyses are small convex faces, projecting at the base of the neural spine.
The remaining cervicals, five in number, are short, all carinate, except the seventh, and opisthocœlous; with the faces expanding only slightly beyond the body of the centrum. A peculiar feature is a small pit upon the convex anterior face, indicating either a ligamentous attachment with the antecedent vertebra, or a remnant of the notochord. This is a feature we have not noticed elsewhere. A long and heavy transverse process supports a large and widely-perforated inferior lamella. The pedicles are quite wide at base, inclosing a large neural canal. The entire upper part of the arch is unfortunately wanting.
The dorsal centra are smaller than the cervical, slightly opisthocœlous, and carinate. They are sub-cylindrical anteriorly, with decided costal surfaces before and behind; approaching the lumbar region they become subtriangular. A high neural arch supports a stout, but never very high neural spine; this projects backwards, keeled in front, expanding and deeply grooved behind. The zygapophyses are small and nearly vertical. There is a short and thick transverse process.
The lumbar vertebræ are long, decidedly opisthocœlous, becoming wider and more depressed as they approach the sacrum. The first sacral vertebra presents the same characteristics as the last lumbar, only the body of the centrum is slightly shorter. It has a very broad pleuropophysial plate. The remaining sacral vertebræ are broad, and very greatly depressed, rapidly decreasing in size. The transverse processes are slender. The very low neural spines anchylose into a long ridge. The number cannot be ascertained, owing to the fragmentary state of the sacrum. The caudals indicate a tail of not very great length; as the neural canal is small and persists in only a few of the anterior vertebræ.
Measurements of Vertebræ.
Pal, major. M.
Atlas, width, including transverse processes ·195
Atlas, length of inferior arch ·082
Atlas, height, including superior and inferior arches ·078
Axis, width, anterior articular faces ·110
Axis, length, excluding odontoid process ·058
Axis, height of neural spine ·096
Axis, length of odontoid process ·025
Seventh cervical, length of centrum ·037
Seventh cervical, width of posterior face ·043
Dorsals, anterior region, length ·038
Dorsals, anterior region, width, articular face ·034
Lumbar, width of posterior face ·058
Lumbar, length of centrum ·056
First sacral, width of anterior face ·059
The ribs, of which great quantities of fragments remain, were slender and not of very great width.
The femur, which is figured in Plate I., has a small head, supported by a short neck. The shaft, very broad below the head, supports the third trochanter one third of the way down; below which it takes a cylindrical form, and expands slightly above the trochlea. The two condyles, separated by a wide and deep popliteal groove, are nearly subequal in size—the internal somewhat the larger, while the trochlea is long, narrow, and symmetrical. The great trochanter rises slightly above the head, and overhangs a long and quite deep digital fossa. The second trochanter is small. The popliteal space is slightly concave.
Tibia.—The proximal end of the tibia is very large, with massive rugosities for muscular attachment. The two proximal faces are subequal, slightly convex, and separated by a prominent spine, which is grooved at the top. The shaft is long, straight, and compressed antero-posteriorly; the anterior ridge on upper third is very high, and expands into the tuberosity, which is enormous; while on the posterior face is a deep fossa just below the head. The distal end of the shaft is remarkably small, with two concave faces—the internal the smallest—with a low oblique ridge dividing them. There is a prominent malleolus.
The fibula (which is a distinct bone) has a small proximal end, and expands slightly below, with a large external malleolus.
Measurements of Limbs.
M.
Femur, total length ·420
Femur, transverse diameter at distal end ·098
Tibia, length ·310
Tibia, transverse diameter, proximal articular face ·090
Tibia, transverse diameter, distal articular face ·077
The pelvis is described from the right and left ilia, which are broken as they expand towards the crest; the acetabulum is fragmentary, but all the parts remain. The ischium and pubis are only represented by fragments. As figured in Plate V., the acetabulum is restored from a somewhat smaller specimen. The most striking feature of the ilium is the long and somewhat constricted neck. The acetabular border is long and curved forward, thinning gradually as it approaches the crest; and marked on the iliac surface, near the acetabulum, by a slight rugosity for the rectus muscle.
The ischial border, while less arched, is probably longer; and the sacral surface, distinctly defined, indicates that the rounded upper border of the ilium rarely reached above the sacral spines. There is a deep groove between the ischial and pubic borders, the latter disappearing about half way up the iliac surface. The gluteal surface near the acetabulum is much depressed; above it expands into a broad, flat, thin plate.
The ischium has a stout neck and thick expansion below; the upper border is very heavy. From what remains of the ischium and pubis we can infer a large elliptical obturator foramen, a short pubic symphysis, a narrow and rather slight pubis, with a small nearly cylindrical neck. The acetabulum is deep, with a thick well-raised border, and a large, oblong, and very deep pit for the ligamentum teres.
Measurements of Pelvis.
M.
Ilium, transverse diameter above acetabulum ·062
Ilium, long diameter (estimated) ·232
Acetabulum, greatest diameter ·050
Ischium, transverse diameter below acetabulum ·041
Pubis, diameter at obturator foramen ·035
The tarsus is arranged in the usual Perissodactyle order. The calcaneum is stout, of good length, tuberous, but not expanding much at the extremity; presenting two faces for the astragalus, of which the internal is the largest, and a large distal face for the cuboid. The astragalus is wide, with less asymmetry in the two articular facets than is common. It articulates with both the cuboid and navicular.
Measurements of Tarsus.
M.
AAstragalus, total width, tibial facets ·048
Astragalus, total length ·056
Astragalus, length, navicular facet ·046
Astragalus, width, navicular facet ·035
Calcaneum, total length ·120
Calcaneum, total breadth ·057
Calcaneum, length of tuber calcis ·050
All the above were found at Henry's Fork Divide. In another locality, in connection with a fine head of P. major, was found the lower half of a humerus.
The shaft is cylindrical and twisted, expanding widely at the distal end. Of the two condyles the external is the largest; and, to quote from Dr. Leidy, "a deep supra-condylar fossa occupies the front of the humerus, opposed by a deeper and more capacious anconeal fossa." The greatest breadth between the supracondyloid eminences is ·091 m.
Palæosyops paludosus, Leidy.
Cont. to Ext. Vert. Faun, P. lævidens Cope. U. S. Geol. Survey of Terrs, 1872, p. 591.
Specific characters.—Second superior molar has but one outer tubercle. The cones are low as compared with P. major. The cingula are much less developed. The angle of the lower ramus is much longer. The zygoma is massive and wide. An internal process on the glenoid cavity. Temporal fossæ very deep. Crest of occiput nearly in same vertical line as occipital condyles.
The full details of P. paludosus, which follow, may seem somewhat unnecessary, to one familiar with the comprehensive work of Dr. Leidy upon the subject. Care has been taken not to retrace any of his steps; and the descriptions given below are of those parts of the animal which he did not possess at the time of writing. They include (1) a cranium perfect posterior to the orbits; (2) a right ramus mandibuli, with full dentition, except the first premolar; (3) portions of the fore-limbs, scapula, and pelvis, pes and manus, and many fragments of other parts.
Among the first discoveries on Cottonwood Creek, in a stratum of fine green sand, was a head of P. paludosus, complete posteriorly, and broken off just behind the orbit. A rear view of this has been admirably figured in Plate I.
General appearance.—The base of the cranium is of great width; the occiput is high, inclined very slightly backwards, and deeply concave from side to side. The forehead is triangular and narrow. The temporal fossa is of immense size and depth, leaving a small intracranial cavity. The zygomas are heavy, and arching widely outwards give this part of the head a strong resemblance to the Felidæ.
Description in detail.—The narrow but prominent basioccipital segment is broadest posteriorly and tapers forwards; divided by a median ridge, which expands anteriorly into a large tuberosity; a feature also characteristic of the tapir. About half an inch in advance of the condyles are the condylar foramina. The condyles are formed of the exoccipitals, which are low and of great lateral expansion. Their junction with the mastoids is marked by a large foramen. The par-occipitals are short and styliform. The supra-occipital region is very large, high, and deeply concave from side to side, much wider than in the tapir, with a marked interparietal suture. The condyles are wide, but not very deep, approaching each other very closely below. The basisphenoids are long and narrow, tapering forwards. The alisphenoids are mutilated, but indicate large vertical ridges joining the parietals, and heavy pterygoid processes, perforated at the base by the alisphenoid canal. They are again perforated by the foramen ovale three fourths of an inch behind this. This completes the base of the skull.
The parietals are very large, they form nearly the whole of the temporal fossil; which, deep and wide, enclosing a small cranial cavity, contrast strongly with the long and shallow temporal fossæ of the tapir. The parietal crest is very broad, and grooved at the top. This high crest and deep adjacent temporal fossæ we at first mistook as pointing to an exclusively carnivorous type. The forehead has a triangular appearance, from the divergence of the two side ridges of the sagittal crest. The postorbital processes are very large, but do not reach the opposing processes of the malar. The orbit is thus left incomplete posteriorly, while in form it greatly resembles that of the Sus. The squamosal encroaches considerably upon the temporal; and sends outwards and downwards a great zygomatic process, which arches outwards from the skull as in the Felidæ, and is more powerful than in any living carnivore (Leidy.) A strong downward direction is especially characteristic, the whole describing a sigmoid curve. The mastoids are of great size vertically, and transversely they are confluent with the par-occipitals. A low, thick process on the internal side of the glenoid cavity prevents lateral motion.
The nasals are long, broad, and thick, convex from side to side, narrowing slightly anteriorly. They are straight, as in Sus, which they resemble more than they do either tapir or rhinoceros. The anterior borders are rounded, and do not reach as far forward as the symphysis of the premaxillary. The malar is broad and thick, probably forming but little of the face, being directed downwards and backwards to meet the zygoma. The postorbital process is short, and rather larger than Dr. Leidy has indicated. The maxillaries, smaller proportionately than in Sus, form posteriorly the floor of the orbit; while the infraorbital foramen is situated over the last premolar. The premaxillaries fail to reach the nasals.
Comparative Measurements of Head.
P. paludosus. P. major. P. Tapir.
M. M. M.
Height of occiput ·122 ·148 ·120
Breadth of occiput at post tympanic processes ·160 ·166 ·110
Breadth of cranium at ends of post-glenoid processes ·172 ·210 ·126
Transverse diameter of occipital foramen ·031 ·049 ·040
Vertical diameter of occipital foramen ·027 ·033 ·027
Depth of occipital condyles ·033 ·039 ·029
Breadth of occipital condyles ·040 ·049 ·041
Breadth at occipital condyles together ·082 ·100 ·082
Width of basioccipital at anterior condyloid foramina ·038 ·039 ·028
Width of basioccipital at junction with basisphenoid ·025 ·032 ·020
Width of crest dividing the temporal fossæ posteriorly ·011 ·020 ·011
Breadth of cranium outside of zygomata ·262 ·280 ·180
Depth of zygoma ·046 ···· ·036
Lower jaw of P. paludosus described from another specimen.
The peculiar feature of this jaw is its remarkable extension back of the molar series (a feature which has not been noticed heretofore), the distance from the last tooth to the angle being greater than the length of the entire molar series. From beneath the last molar, the lower margin curves gently up to the symphysis. The alveolar border is but slightly curved. Behind the last molar the lower margin forms a sigmoid curve, much more decided than in P. major (first upwards and then downwards), and the ramus thins out rapidly to the angle, where it has a slightly raised border; at the diastema the ramus curves outwards so as to throw the canines out of the line of the molars. The symphysis is long.
Dentition.—The incisors, three in number, from length and shape indicate a semi-circular arrangement, as in most Perissodactyles. They increase from first to third. The crown of the first resembles very much that of the ruminants, but has a straight posterior basal ridge. Its forward edge is worn so as to expose a small tract of dentine. The second is larger, but very much like the first in conformation; while the third has an acute conical crown with a strong basal ridge.
Of the premolars the first is wanting in this specimen. The second is bilobed, the anterior lobe much the larger. It has a small accessory tubercle on its anterior slope. The outer face is rounded, the inner nearly flat. The posterior lobe is very small and obtuse, and with the inner face slightly grooved. In third and fourth the valley between the lobes and the groove on their faces enlarge; while the anterior lobe becomes relatively smaller.
Measurements of Lower Jaw.
M.
Diastema between canine and first premolar ·024
Length of entire molar series ·143
Distance between last molar and extremity of angle ·147
Depth of jaw at last molar ·070
Among the first discoveries on Cottonwood Creek, in connection with the lower jaw of P. paludosus just described, were an ulna and radius, and part of the manus and scapula of the same. These have been figured, together with other fragments belonging to the same species, in Plate III., and form an interesting complement to the nearly complete hind limb of P. major previously described.
The scapula has a shallow oval glenoid cavity, which is concave longitudinally. Separated from it by a narrow notch is a strongly recurved coracoid, placed on the inner side of the bone. Above the coracoid the border is thin, and arches inwards and then forwards; while the glenoid border is much straighter, rising from a slight tuberosity. The spine rises gradually from the glenoid, and does not bear any indication of an acromion.
The humerus is represented by proximal and distal extremities. The latter presents the same characters on a smaller scale as in P. major. Upon the proximal end there is a deep bicipital groove. The greater tuberosity has a hooked anterior projection, and runs back into a ridge behind. (See Fig 7, Plate III.)
The proximal end of the ulna (of median breadth anteriorly) narrows into a prominent ridge behind. This gives a trihedral character to the shaft. This is persistent, but is less marked as the fore-and-aft diameter decreases. The remaining features of note are a high tuberous olecranon expanding behind; a shallow sigmoid, divided by a deep fossa into two long divergent articular faces; a trihedral shaft tapering slightly, but distinct from the radius; a narrow distal extremity, with a small irregular face for the cuneiform.
The radius has a rather short shaft, curved forwards, expanding below, and placed immediately in front of the ulna. A strong ridge runs from the external tuberosity up the posterior face of the shaft, disappearing two inches from the top. The proximal end, fitting against the ulna by two small faces, forms the greater part of the elbow-joint, a strong median ridge dividing the proximal face into two subequal surfaces with well-raised borders. The distal end of the shaft is rugose, and more prominent than the proximal. It has an oblong transverse face, which is slightly concave fore and aft. The position of the radius, immediately in front of the ulna, and its manner of articulation, remove any possibility of rotation, a feature in strong contrast with what we should expect from the character of the head.
Measurements of Ulna and Radius.
M.
Ulna, length, excluding olecranon ·224
Ulna, length of olecranon ·080
Ulna, transverse diameter, proximal surfaces ·041
Ulna, diameter of shaft at median line ·038
Ulna, fore-and-aft diameter, distal face ·025
Ulna, transverse diameter, distal face ·017
Radius, proximal face, transverse ·048
Radius, proximal lace, fore-and-aft ·030
Radius, median diameter, shaft ·019
Radius, median diameter distal face, transverse ·043
Radius, median diameter distal face, fore-and-aft ·016
The manus is described from the third and fourth metatarsals, with three phalanges. The metatarsals are short, with a wide, stout shaft, flat in front and slightly arched forwards behind. The proximal ends unite and form a continuous articular face, concave from side to side; while upon the exposed sides are smooth facets, indicating the presence of two additional toes of less size. (See Plate III.) The convex distal faces are marked behind by a slight groove.
The phalanges are very short and broad, the lower facets marked by a shallow median groove. The ungual phalanx is wide and short, with a crescentic outline.
Measurements.
M.
Third metatarsal, total length ·090
Third metatarsal, transverse diameter, proximal face ·017
Third metatarsal, transverse diameter, distal end ·019
Second phalanx, length ·024
Third phalanx ·014
Total estimated length of manus (6 inches) ·155
Palæosyops vallidens, Cope.
Proceedings Am. Phil. Society, 1872, p. 487; Hayden's Survey, 1872, p. 572.
Specific characters.—Founded on details of dental structure. Superior size. In the upper molars two strong transverse ridges connect the inner tubercle with the outer crescents, inclosing a pit between them. In the premolars the outer crescents fuse almost into a single ridge. These united crescents are relatively narrower. The inner molars are also narrower, and the posterior tubercle of the last is an elevated cone.
Fragment of a lower jaw containing the two posterior molars. The measurements of the teeth are identical with those given by Professor Cope. The depth of the ramus below the last molar is three and one third inches, and it is slightly heavier below than in P. major.
Restoration of Palæosyops.—The elevation of Palæosyops major, which is taken as a type, was approximately the same as that of Palæotherium magnum as restored by Cuvier.
The nearly complete ilium, femur, tibia, and tarsus of P. major in our possession, enable us to make the following estimate of the elevation of the hind quarters.
INCHES.
Pelvis, height of ilium above acetabulum 9
Femur and tibia by actual measurement, allowing for bend at the knee 26
Tarsus, from astragalus, and cuboid 3
Metatarsus and phalanges (estimated from manus of P. paludosus) 8
46
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.
This species is intermediate in size between H. agrarius and H. modestus. As in the latter species; the basal ridge extends around the entire crown of the tooth, with a small interruption on the antero-external lobe. It is more pronounced, in front and less behind than in H. imperialis. The anterior conical buttress is not nearly so well developed as in H. imperialis; the valleys are wide, and the descending fold from the antero-external lobe is obscure, scarcely marked at all in the first. The transverse crests are strongly arched forwards, and the anterior is very much the longer. The peculiar feature of the species is the position of the postero-externa, lobe, which is pushed to the posterior aspect of the tooth; this is carried so far in the last molar that the two external lobes stand on nearly the same transverse line. The antero-external lobe is much the highest point in the tooth, and its the first molar is remarkably sharp. The enamel is considerably wrinkled, but not nearly so much as in H. modestus.
Measurements.
M.
Length of first molar ·012
Breadth of first molar ·0155
Length of second molar ·015
Breadth of second molar ·017
Length of third molar ·0145
Breadth of third molar ·017
From Cottonwood Creek.
Hyrachyus nanus, Leidy.
Pr. Ac. Nat. Sc., 1872, 20.
Henry's Fork.
Hyrachyus agrarius, Leidy.
Pr. Ac. Nat. Sc., 1871, 229.
Henry's Fork.
Hyrachyus eximius, Leidy.
Pr. Ac. Nat. Sc., 1871, 229.
Cottonwood Creek.
Hyrachyus crassidens, sp. nov.
Established on the left and a portion of the right ramus mandibuli, containing the first molar.
The jaw presents some differences from the form common in Hyrachyus. The alveolus is more curved, especially near the ascending portion of the ramus; the jaw is narrower, and is especially contracted near the incisive alveolus. The lower margin of the ramus is but slightly curved. The ramus itself thickens regularly from before backwards, and is thickest at the last molar; beyond which it becomes thinner again. The depth of the jaw is comparatively small, and the teeth have a forward inclination; the mental foramina are not so large as in other species of Hyrachyus, and are four in number.
The incisors are small, arranged in a semi-circle, and have very much compressed fangs, with somewhat procumbent crowns; the canines are small, and form a continuous series with the incisors. There is a diastema between the canine and first premolar; but one which is shorter than in known species of the genus, and which does not indicate the usual curve of the upper border of the ramus.
The molar series, (so far as can be judged from their broken condition), are much the same as in other species; except, perhaps, in the greater relative size of the posterior lobes, and in the more complete closing of the median valley by the junction of the two lobes externally. The ridge which curves downwards and inwards from the external point of the anterior lobe is unusually well developed, and curves across the entire crown. The cingulum is feebly shown; it appears on the anterior and posterior ends of the tooth (first molar) and for a very short distance on the outside of the tooth opposite the median valley; there is no trace of it on the inner side.
Measurements.
M.
Length of entire molar series (about) ·080
Length of premolar series ·033
Length of true molar series (about) ·047
Fore-and-aft diameter of fang of canine ·008
Distance between canine alveoli ·009
Length of diastema ·115
Length of the first molar ·015
Breadth of the first molar ·010
Depth of ramus below last molar ·0245
Depth of ramus below last premolar ·0215
Greatest thickness of ramus ·017
Length of symphysis (about) ·030
Found at Henry's Fork.
Hyrachyus ———— ?
There are three premolars of the upper jaw which we cannot refer to any known species; but they are too imperfect to justify the formation of a new species for their reception.
What appears to be a first premolar is inserted by a single broad fang; it is too much worn to show the characteristic enamel folding, and is peculiarly broad and short. The second premolar shows the usual foldings of Hyrachyus; save that a distinct valley enters the tooth from the posterior edge, running forward to the transverse crest, and inclosed by the curving backwards of the internal cone. The crown is nearly square; the basal ridge is scarcely marked at all.
Measurements.
M.
Length of first premolar ·011
Breadth of first premolar ·016
Length of second premolar ·012
Breadth of second premolar ·014
HELALETES, Marsh.
Am. Journ. Sc. and Arts, 1872, p. 218.
Additional material enables us to give further characteristics of this genus, which may be thus defined: Mammals, allied to Lophiodon, having a third lobe to the last lower molar, short symphysis, and with the teeth of the lower jaw forming a continuous series. Astragalus has narrow, oblique condyles.
Dental formula: I. ? - ? , C 1 - 1 , Pm. 4 - 4 , M. 3 - 3
3 - 3 1 - 1 4 - 4 3 - 3
Synopsis of Species.
A. Teeth small; a small tubercle on the outer margin, between the cusps of last upper molar H. boöps.
B. Teeth much larger and proportionately broader; no tubercle on last upper molar H. latidens.
Helaletes latidens, sp. nov.
Lower Jaw.—The ramus is stout, and resembles in general form that of Hyrachyus, but the alveolar border is straighter than in that genus; the ascending portion forms a right angle with the horizontal portion, and the masseteric fossa is deep. The symphysis is comparatively short, and there is complete bony union between the rami, which do not diverge so much as in Hyrachyus. As in that genus, there are several small mental foramina beneath the premolar series. The dental series forms a nearly continuous line, the only diastema being a very short one between the first and second premolars. The incisors have compressed fangs, and are arranged in a slight curve. The canine is small and subcircular at base. The premolars also are small; they somewhat resemble those of Hyrachyus in shape, but are smaller, and have the posterior lobe not so well developed. The first is implanted by a single fang, the others by two. The molars (except the last) consist of two pyramidal lobes, which form transverse cutting-crests, as in Tapirus and Hyrachyus. The basal ridge is shown on the anterior and internal sides only. Externally the lobes meet at their bases, inclosing the valley on that side. The last molar is by far the longest of the series, and consists of three lobes, of which the anterior is the largest, and the posterior the smallest. The basal ridge at the anterior part of the tooth is very strongly marked.
Upper Jaw.—The molars increase in size from first to last with considerable regularity. The premolars are small, and, as in Hyrachyus, have one single internal cone, which is joined by transverse ridges from the two outer cusps; the anterior accessory tubercle is well developed. The first molar is considerably larger than the last premolar; it is much worn, and does not show anything more than that there are two internal cones. The anterior conical buttress is very largely developed throughout the true molar series. The second and third molars resemble almost precisely the corresponding teeth of Hyrachyus. Their shape, however, is more nearly square than is usual in that genus.
Measurements.
UPPER JAW.
M.
Length of true molar series ·036
Length of last molar ·0135
Width of last molar ·015
Length of second molar ·012
Breadth of second molar ·015
Length of first molar ·0105
Breadth of first molar ·012
Length of last premolar ·009
Breadth of last premolar ·011
Length of third premolar ·008
Breadth of third premolar ·009
LOWER JAW.
M.
Length of true molar series ·042
Length of last molar ·018
Breadth of last molar ·009
Length of second molar ·013
Breadth of second molar ·008
Length of first molar ·012
Breadth of first molar ·008
Length of third premolar ·008
Breadth of third premolar ·005
Diameter of canine at base ·006
Length of symphysis (about) ·027
Found at Henry's Fork.