The frontal bones are broad, projecting laterally in strong postorbital processes, which, with those from the jugals, almost close the orbit behind. The premaxillae are peculiar in having a median crest on the upper surface, the top of the crest being rugose, as though in life it had continued upward as a cartilage septum. The maxillae rise well up on the sides of the skull, bounding the lower part of the orbit, and having a short zygomatic process. The small lachrymal is but little exposed on the exterior surface of the skull, the lachrymal pit being well inside the orbit. The zygomatic arches are broad and heavy, and composed mostly of the wide jugal bones. The palate is highly arched and relatively narrow, the crowns of the premolars and molars projecting inward over it, thus narrowing it still more. It extends back well beyond the last molar. The large tympanic bullae are hollow, and the cavity in the squamosum seems to be reduced in size, as compared with Rhynchippidae or Nesodontidae. The occipital condyles are set well apart and are sessile; and the paroccipital processes are long and slender.

The atlas, axis and cervical 3 are associated with the skulls. The atlas is short, heavy, and has the anterior cotyles broad, deeply excavated and wide apart; while the posterior cotyles are nearly flat, and high as well as wide. The transverse processes are only moderately wide, but are very heavy, especially along the posterior margin. The centrum of the axis is flattened, the neural canal, wider than high, and the neural spine of moderate height. The anterior cotyles are broad and moderately convex, and the odontoid process is a stout peg-like process, somewhat higher than wide. Slender transverse processes project sharply from the centrum, and have at their bases a large canal for the vertebral artery. Cervical 3 is shorter than the axis, has a less depressed centrum, a small neural spine, and short wide transverse processes.

Though I have skulls and jaws to represent some twenty-five individuals, no limb material was found in direct association with any of them. However we did find a humerus, radius and ulna on the same level and about fifteen feet from one of the skulls, and as it corresponds in size, and as humeri of this type are the most abundant skeletal bones found (as is also the case with the skulls), I have considered it proper to associate these fore limb bones with these skulls. The humerus is a stout bone, of medium length, with a large sessile, and but little rounded head. The external tuberosity is wide, thick and projects a little above the head, while the internal tuberosity is so small as to be almost negligible. The shaft is flattened laterally at the upper end, but distally is compressed in the antero-posterior direction. The supratrochlear fossa is shallow, the anconeal deep, but there is no foramen connecting them. The external condyle is small, the internal much larger. The trochlea is narrow, with a swollen articular area for the radius, and a wider saddle-like one for the ulna. The ulna is a stout, nearly straight bone, slightly longer than the humerus. The olecranon process, though large, is not excessive. The sigmoid notch makes a deep semicircular cavity, with the articular facets expanding on either side. It was closely fitted to the radius so as to allow little or no rotary motion of the forearm. The facet for the radius is a narrow band-like area just below the sigmoid notch. The shaft is almost rectangular in section. Distally the ulna contracts sharply into a heavy styloid process, on the end of which is a large convex facet for the pyramidal, which merges without interruption into the facet for the pisiform. The radius is a slenderer bone, with a relatively small proximal head, but distally expanded into a much larger articular end. My specimen is considerably weathered, but shows a wide shallow articular facet for the humerus, and a band-like facet for the ulna, but otherwise it gives little more than the length.

Of the hind limb, Gaudry[16] figures the astragulus and the calcaneum, the former short and with a low trochlea, the latter also short and with a broad facet for the fibula. Gaudry also states that the foot was tridactyl and plantigrade, but I am doubtful of the plantigrade feature.

Ameghino has made six species of this genus, L. gaudryi, L. fissicola, L. lapidosa, L. oxyrhynca, L. stenognatha, and L. garzoni. All of the first five are described as of the same size as L. gaudryi. L. garzoni is a smaller, about 60 per cent. of the size of the others. Of the first five listed, the first three have the large incisor and I consider them all L. gaudryi. L. oxyrhynca and L. stenognatha are described as having small canines and I believe that this is a sexual difference only, so have considered these two species as also belonging to L. gaudryi, but females. I have made a careful comparison of L. gaudryi and L. oxyrhynca and find them identical in all the features except in the region of the canines where the latter is weaker, and can see no more than sexual differences. Usually with this weakness of the canine goes a smaller or lighter build of the lower jaw which is what would be expected. The points by which the various species were differentiated were, beside the size of the canine, the presence or absence of pit 3, and the variation in the foldings on the outer sides of the lower molars, which I find on sectioning a tooth appear deeper or shallower according to whether the tooth was more or less worn.

Leontinia gaudryi Ameghino

Fig. 69. Right
upper
dentition—
½ natural size.