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Show 71 H. paniense, Cope, and differs from the H. occidenlale, H. speciosum, and H. gratum of Leidy in the relative form and size of the internal anterior dentinal column. In the two species first named, this colnmn is subcylindric and equal to, or smaller than, the posterior internal columnar fold; in the three species last named, the anterior column is flattened or oval in section, and often larger than the posterior columnar fold, and Bubraedian in position. In the typical or New Mexican specimen, the anterior column is large, and its center is anterior to the middle transverse line of the crown. In the present state of attrition, which has left two- thirds of the crowns of the median molars, this column presents an angular projection toward the inner anterior crescent, betraying an approach to the union seen in Protohippus, which is in the fifth molar of the right side of the present horse actually accomplished through the medium of a narrow isthmus. The dentinal baud connecting the inner crescents throws out two, rarely one, folds toward this column. The borders of the lakes are much plicate; the posterior border of the anterior lake having from four to six inflections. The posterior border of the posterior lake exhibits one deep inflection, which is generally bifurcate. The first premolar is quite small, and is two- rooted; the second is a wide tooth, different in form from the elongate corresponding tooth of the H. occidentals; its anterior lobe being but little prominent. The palate is wide and well arched. The mandibular teeth are elongate but not narrow ; and the interior lobes are well developed, especially the median ones. No basal cingula on teeth of either jaw. The last molar is smaller than the three preceding it, and the anterior lobe of the first is quite narrow. The molars of oue ot the specimens from Colorado are closely similar in all respects except that the anterior lobe of the second premolar is a little more produced. I also refer here the tooth described as " M. 2 " under H. panieme in Report of the United States Geological Survey of the Territories, 1873, p. 522- 523. As compared with the molars of that species, those of H. calamarium differ in the much greater complexity of the eoamel folds; those of the H. paniense being the simplest in the genus, even more so than in H. affine. The anterior inner column of H. paniense lacks the characteristic inner angle seeti in tho present horse. Measurements. M. Length of seven superior molars , 134 Length of three true molars 062 Length of second premolar 026 Width of crown of second premolar 020 Greatest length of second premolar 022 Greatest width of second premolar 024 Greatest length of penultimate molars.. r 022 Greatest width of penultimate molars 022 Width of palate ( chord) between middles of third premolars 042 Length of crown of antepenultimate lower molar 021 Width of crown of antepenultimate lower molar .012 The typical specimen belongs to an adult animal, and was taken from the matrix by myself, without admixture of others. Hippotherium speciosum, Leidy, Extinct Mammalia of Dakota and Nebraska, p. 282. Series of superior molars nearly identical in character with those originally described as typical of this species by Dr. Leidy, and figured on Plate XVIII, Figs. 16, 18; 19, of the work above quoted, and agreeing with specimens from Colorado. Some of the specimens described by Dr. Leidy as of doubtful reference under the head of this species obviously do not belong to it. Protohippus, spec, indct. A single much- worn molar, of the size of that of P, sejunctus, apparently represents this genus. The specimens obtained indicate another species of horse, but they are not sufficiently characteristic for determination. Aphelops meridianus, Leidy.- Rhinoceros meridian us, Leidy, Extinct Mammalia of Dakota and Nebraska, p. 229. Remains of rhinoceros are not rare in the deposits of the ancient lake of the Rio Grande valley, and among the most complete fossils obtained is the greater part of the cranium of a species allied to the Aphelops megalodus of the corresponding beds of Colorado. The specimen includes the dentition of both jaws, which exhibits the following formula: I. $; CO; Pin. $; M. $. The absence of the first premolar distinguishes the form from the Miocene Accdatheriumas well as from the existing genua Rhinoceros; while the presence of inferior incisors separate it at once from the living Rhinaster. I have named this genua Aphelops; like Aceratherium, it is hornless. To it are referred, |
