OCR Text |
Show 116 qnently 45°, sometimes50°, to the west and southwest, and containing numerous fossils, as Inoceramus, etc. The upper sandstones of this formation pass into a brackish or fresh- water formation, which includes a bed of lignite, of sometimes 50 feet in thickness. Above this rests, couformably where seen, a moderate thickness of rather soft marine rocks, containing numerous shells, Jcephala, Gastropoda, aud Cephalopoda, including 0g9terst Bacnlites, and Ammonite* resembling A. placenta most, with sharks' teetb. Resting unconformably on* these, with a much reduced dip, is a mass of brown and reddish sandstoues, some 1,500 feet in thickness, inclining perhaps 10° south and southeast. These pass continuously into the superincumbent red and gray marls, alternating with brown aud white sandstone of the fossiliferous beds of the Eocene. The observed part of these beds is about 1,500 feet in depth. A considerable number of species of Verttbrata have been obtained, a large majority of which are Mammalia. While it is premature to attempt to determine fully the character of the fauna, enough has beeu ascertained to indicate marked differences from that of the Bridger group of Wyoming. It is peculiar iu the entire absence of the genus Palwosyopsos, so characteristic of the former, and its replacement by Bathmodon, which has never been recorded from the Bridger formation. The abundant species of Hyrachyus of the Bridger are here represented by a single one of small size, which occurs but rarely, while its companion, Hyopsodus, is very rare or wanting. While gar- remains are abundant in both, the Amiidte and Sihtrida? have not yet rewarded our examinations. The characteristic genera of the New Mexican fauua are Bathmodon, Cope; Hipposyus, Leidy; aud Phtnacodus, Cope, genera which it shares with the Bathmodon bed of the Green River formation of the Bear River Wyomiug. There is in all respects so close a resemblauce between these deposits as to lead to the belief in their horizontal identity, and with other reasons, to give to the southern basin a higher antiquity than belongs to the celebrated Bridger series. The interesting fact that the teeth of six or seven species of sharks and one Oatrea have beeu deposited with tho mammalian remains indicates that the marine Cretaceous rocks formed the coast- material of this lake, and the earlier period of its deposit is probable on various grounds, to be considered at a future time. The facts are all confirmatory of tho view already expressed by the writer that the population of the Bridger epoch was derived by migration from a southern region. Perhaps the most important addition to paleontological science obtained daring the course of the investigation is the discovery of four species of two new genera, CaTamo-don and Ecioganm of Toxodontia, an order which has not been heretofore identitled as having existed on the North American continent. DESCRIPTION OF SPECIES. ECTOGANUS GLIRIFORMIS, gen. et sp. nov. Char. gen.- This genus rests on a number of remains of the crania of three species> ncluding principally teeth, iu a good state of preservation, all found in approp/ vsrfe relations by tho writer. The teeth include incisors, molars, aud premolars, it is believ ed, of both superior aud iuferior series. There arc two types of gliriform incisor- teeth, and of one of these in the largest species three sizes. In the one, the teeth are elongate, compressed, convex in both directions on the anterior; are convex or angulate in section at the posterior face. In all, the enamel is confined to a band ou the anterior face, extending more or less on one side or the other, the uaked dentine extending prominently backward at the middle aud basal portion of the shaft. In the larger size, this portion is subacute behind; in the smaller, obtuse. Teeth of this type are of three sizes, the smaller two the most compressed and with narrowest enamel. Those of the second type are of one, an intermediate size, and are shorter than those of the others and less compressed. One of their faces is concave in both directions, and is covered with enamel from the apex of the tooth for some distance posteriorly. From its termiuus on the concave side, the enamel borders retire to the sides of the convex front. There are three molars of the superior and many of the inferior series available for present determination. The superior are all remarkable for the great exposure of their external faces as compared with their internal, and the extension of the enamel on the outer face of the very thick external root, which is not distinguished from the crown. The true molar has three roots, and the crown is longer antero- posteriorly than transversely. It consists of two transverse tubercular ridges, connected by a medium oblique longitudinal ridge. The premolars have two of the roots connate, forming a support to the greater part of the crown. The worn surface is in form somethiug like the Greek v, the deep emargination being internal. The inferior molars have greater anteroposterior than transverse diameters. The enamel is more extended on one side than the other, covering the exposed portions of the roots. The grinding surface is plane, aud has the form of a horizontal •: » ; the limbs being angulate, as in the Greek 2. It isimpossible to determine the affinities of this curious genus with the material |