OCR Text |
Show 128 The first premolar is one- rooted; the second and third are without posterior coronal lobes, but exhibit small basal lobes, both anterior and posterior. The anterior of the second is rather elevated, and the entire crown is directed obliquely forward. Canine compressed; mental Ibrainiua below the second and third premolars. Measurements. M. Length of three premolars 006 Elevation of auterior lobe of sectorial 0U2 Depth of ramus at anterior lobe of sectorial 003 This species is of smaller size than the M. viuatelinus, Cope, and the sectorial tooth less elevated and trenchant. COSOUYX KAMOSUS, sp. nov. Char, gen.- Inferior molars prismatic, § ; the premolars all sectorial, last with short branch- crests. Molars with basal iutercolumuar tubercles. Horns superciliary, solid, branched. This geuus was indicated by Dr. Leidy from a horn of the species known to* him, the Conoryx furcatus, from the Pliocene beds of the Niobrara. The same or a similar species has left abundant remains in the Santa Pc~ marls, and, in connection with the more numerous C. ramosus, has euabled me to determiue the dental and other characters of the genus. After a careful examination of the horns of these species in my possession, those of eighteen individuals ( at least I find that of ten where the basal portion is preserved) the beam has been brokeu off and reunited by anchylosis in six. In most of these the spot is marked by a ring of exostosed tuberosities, like those constituting the burr of the doer's horn. On a specimen of this character, pertaining to u third species, Professor Leidy based his Cevviis tcarrenii, which may now be called Coaoryx icarreuii. It is abundant in the Santa Fe marls. The fracture has taken place in every instance at a poiut as far above the frontal^ bone as the burr of deer is situated, and is irregular in outline, higher on the ouo side* than the other. In some of the specimens the smaller antlers are also broken, and exhibit a similar burr, but the terminal portion is usually lost. In one specimen, a broken antler is anchylosed in the usual manner of overlapping ends. The horns are solid, the center having a narrow, spongy axis. The surface is dense and marked by arterial grooves, but not pierced by noticeable foramiua. It is evidently a question whether this genus should be referred to the hollow or solid-horned Iinnriuantia ; to the Borida; or Cerridte. The horns might be regarded as those of deer were it not for the occasional specimens without burr, while the teeth are both cervine and bovine. We way here draw such inferences as we caii respecting the nature of the covering of the horn. That the fractured beam should not be lost indicates the presence of some kind of covering to retain it. That this covering was not horny is probable from the fact that the horns are branched, a structure impossible to the Borhhv, since antlers effectually prevent the usual mode of increase of horn by additions at the base and removal at the extremity. That such covering protected arteries, which aided in the production of burrs, is also probable. We may thus believe it to have been dermal like that of the giraffe, or the A ntilocapra, at the period of immaturity cf its horny sheath. It may be concluded, then, that the genus Cosoryx represents the ancestral type of the (\ rrida\ and explains the origin of the remarkable type of horns of that family as follows: Ruminants with fixed horns of structure more dense and brittle than others of the same type, in Their annual combats at the rutting- season, very frequently broke the beams or! not far above the base. The usual location of nutrition followed, which, being annually repeated, became a& periodical in its return as the activity of nutrition of the reproductive system. This activity ceasing, the horn, being dense, lost its vitality, the more so as the normal covering would have already perished in its distal portions. The natural consequence, the separation of the dead from the living bone by suppuration, would follow. This process would, however, probably require a longer time for the establishment of its periodical return thau the fracture and attachment of the existing horn. - This appears to be the only explanation of the origin of the phenomena exhibited by the horns of the Cerndtv, and is suggested by the specimens of Cosoryx to be described. Char, spevlf.- This species is larger than the C. fnrcatus, Leidy, and differs from the C. tcarrenii in possessing two antlers instead of one, of which the first is given off at a point much farther from the base than in that species. The beam near the base is curved a little inward, and is semicircular in section, the outer face being slightly concave, the inner very convex. The base is situated a short distance within the tree superciliary border. The beam becomes more c vlindrie, and then, expanding in a fore and aft direction, gives off an antler at right angles nearly parallel to the cranial axis. At a distauce little over half the elevation of the first antler, the beam gives off a second in a plane tranverse to the axis of the skull. The terminal X> ortiou of the beam is cylindric, curved, and acute at the apex. |