THE AMERICAN JOURNAL OF SCIENCE [FIFTH SERIES.] ART. XIV.-John Day Promerycochari, with Descriptions of Five New Species and One New Subgenus; by MALCOLM RUTHERFORD THORPE. [Contributions from the Othniel Charles Marsh Publication Fund, Peabody Museum, Yale University, New Haven, Conn.] Introduction. Geological sketch. TABLE OF CONTENTS. Geographic distribution of species. Promerycocharus superbus (Leidy). P. chelydra (Cope). P. macrostegus (Cope). P. leidyi (Bettany). P. lulli, sp. nov. Synopsis of John Day species. P. inflatus, sp. nov. P. marshi, sp. nov. P. microcephalus, sp. nov. Desmatochorus curvidens, subgen. et sp. nov. INTRODUCTION. One of the most remarkable features of the specimens of the John Day genus Promerycocharus in the Marsh Collection is the unusual variation shown in the tooth structure. Styles are developed on the molar teeth, both from the cingulum and from the cone itself, with such frequency that they become of no value for specific determinations. The metastyles of M3 exhibit great variation in size and in robustness, as well as in the degree of inward rotation. Likewise, there is variation in the proportions of size between the superior molars in different individuals. It is interesting to note in this connection that the paratype of Merycochorus proprius Leidy1 has 1 Joseph Leidy, Jour. Acad. Nat. Sci., Philadelphia (2), 7, 110, 380, pl. 10, fig. 5, 1869. This paratype is No. 445, U. S. National Museum, and was found near Ft. Laramie, Wyo. AM. JOUR. SCI.-FIFTH SERIES, VOL. I, No. 3.-MARCH, 1921. a small style developed from the hypocone, of which it is an integral part. There is also great variation in the size, shape, and curvature of the zygomatic process, including the malar below the orbit. These variations do not correlate with the size of the canine, and do not appear to be a sexual character, as Scott pointed out, and as studies of the present material likewise show. The development of the zygoma in this group is so remarkable as well as unusual that it must possess considerable significance. The chief function was apparently to furnish sufficient surface for attachment for the powerful muscles necessary in the mastication of the coarse food upon which these animals subsisted. It has been suggested that these processes may indicate the presence of some external embellishment, as for example, the excrescences on the African wart-hog. There is likewise a very marked variation in the various skull elements, while the various parts of the skeleton have changed but very little, except in size, from those of the earlier Eporeodons. This variation is due, probably, to some external causes which are reflected in the skull, where the greatest evolution is localized in all of the genera of the Oreodontidæ (Merycoidodontidae). The John Day representatives of the genus Promerycochorus became extinct, so far as now known, with the close of the Oligocene. To what causes these variations and extinction are due, is not clear. Possibly a changing climate with its concomitant floral changes was responsible, or a different environment caused by the former habitat becoming uninhabitable through the influx of poisonous gases, or ash falls occurring with sufficient frequency and volume to render the area barren and devoid of life. Racial old age or emigration may have been contributing factors. The chief consideration is that this group of large animals became extinct and that, before extinction, they had begun to vary to a great degree. Many other groups also became extinct in this basin with the end of Oligocene times, such as Eporeodon, Agriochorus, Mesohippus, Protapirus, Elotherium, and many of the carnivores and rodents. In connection with the present study of Promerycochorus, the writer wishes to express his appreciation of the courtesy shown him by Messrs. Matthew and Granger, 2 W. B. Scott, Trans. Amer. Philos. Soc., 17, 151, 1893. of the American Museum of Natural History, in allowing him to measure and study the Cope types of this genus. The illustrations of the new species were made by Mr. Rudolf Weber. GEOLOGICAL SKETCH. In view of the fact that the specimens of fossil vertebrates in the Marsh Collection, from the John Day formation, obtained approximately fifty years ago, are now being intensively studied and described, it is interesting to note that Professor Marsh wrote the earliest general discussion of the geology of this basin of deposition, and that he first proposed the name, John Day, for these deposits. This name has become firmly established in geologic nomenclature in spite of the many substitutes which have been proposed. In 1875, Marsh wrote: "The Blue Mountains formed the eastern and southern shores of this lake, but its other limits are difficult to ascertain, as this whole country has since been deeply buried by successive outflows of volcanic rocks. It is only where the latter have been washed away that the lake deposits can be examined. The discovery and first explorations in this basin were made by Rev. Thomas Condon, the present state geologist of Oregon. The typical localities of this Miocene basin are along the John Day River, and this name may very properly be used to designate the lake-basin. The strata in this basin are more or less inclined, and of great thickness. One section, near the John Day River, examined by the writer in 1871, and again in 1873, seems to indicate a thickness of not less than 5,000 feet. The upper beds alone of this series correspond to the deposits in the White River basin. The lower portion also is clearly Miocene, as shown by its vertebrate fauna, which differs in many respects from that above. Beneath these strata are seen, at a few localities, the Eocene beds containing fossil plants, mentioned above. They are more highly inclined than the Miocene beds, and some of them show that they have been subjected to heat. The inferior strata elsewhere are Mesozoic, and apparently Cretaceous. Above the Miocene strata, Pliocene beds are seen in a few places, but the basalt covers nearly all." This basalt is the Columbia lava flow which delimits the upward range of the John Day. The estimate of 5,000 feet, made above, seems somewhat excessive, although southerly at Logan Butte the strata exceed O. C. Marsh, this Journal (2), 9, 52. 4,000 feet, while north of the mountains in the fossil localities, Merriam1 considers that the John Day does not. exceed a thickness of much over 2,000 feet. The John Day formation is divided into three levels, designated as lower, middle, and upper. Paleontologically, the lower has no designation, but the middle is termed the Diceratherium zone (Wortman), and the upper the Promerycocharus zone (formerly Merycochorus). The writer considers the designation of the middle zone a misnomer. Lower John Day. This division of the John Day is practically barren of fossils. It lies unconformably upon the Upper Eocene Clarno formation, and consists of red, white, and green tufaceous shales. Collier, however, says it overlies the Clarno "with apparent conformity. This division is between 200 and 300 feet thick and the shale is soft and easily eroded. The characteristic erosion topography consists of low rounded mud-covered domes. Collier considers these beds of possible Eocene age, to be regarded as part of the Clarno. Middle John Day. This division is characterized by drab and bluish green andesitic tuffs, ranging in thickness from 500 feet at Turtle Cove to 1,000 feet at Bridge Creek. Thin rhyolitic flows are interbedded in the strata. Erosion sometimes produces rounded hills, but more often steep pinnacles and cliffs. Layers of nodules are common and characteristic, in contrast to both the lower and upper divisions. This middle division has furnished the greater number of fossils. The structure shows some tilting and deformation of the strata but not to as great a degree as the lower division. Upper John Day.-The upper John Day, 300 to 400 feet thick, is composed chiefly of buff colored tuffs or ash deposits, often overlain by sand and gravels at the top. Erosion produces steep cliffs and bluffs. At Bridge Creek and Turtle Cove the whole section of the John Day is exposed, while at Clarno the lower and middle beds are well shown. Along Haystack Valley, chiefly upper, but some middle strata are exposed. The 4 J. C. Merriam, Univ. Calif., Bull. Dept. Geology, vol. 2, 293, 1901. 5 J. C. Merriam and W. J. Sinclair, Univ. Calif., Bull. Dept. Geology, vol. 5, 173, 1907. A. J. Collier, Min. Res. of Oregon, Oregon Bur. Mines and Geology, 1, 13, 1914. 7 Op. cit., p. 14. lower division is apparently the most disturbed, while the middle and upper are but slightly folded, faulted, and tilted in different localities. The mode of deposition of the John Day is still an open question, but in general, the sediments were probably laid down chiefly by æolian, but partly by fluviatile agencies, and not wholly by lacustrine as many writers formerly supposed. Whether the ash was poured out in great volume from neighboring vents or whether it was gradually blown into the atmosphere can not be definitely decided at present. If the former, it must have caused the death of great numbers of individuals, and the fact that many specimens of Eporeodon and Promerycochorus with milk dentition are represented in the collection may have some bearing on the question, which further studies may help to solve. On The geology of the North Fork of the John Day River is but little known, although it is one of the critical areas of this basin. Geologically, it is important as showing a divergence from the typical John Day formation as elsewhere exposed, in that it exhibits red beds at or near the top. At all other localities in this area, the red beds are apparently confined to the lower John Day. At least one fossil horizon is dark chocolate in color of matrix. Other geologic peculiarities exist in this locality, which are not pertinent to so brief a discussion as this one. the whole, these beds are probably mainly upper John Day with perhaps some exposures of the middle. Paleontologically, the North Fork fauna is different from that of the rest of the basin. Two of the new species herein. described were found in this area. Cope indicated this faunal distinction in 1884, and the material of other groups in the Marsh Collection, in so far as it has been worked up and studied, points to the same conclusion. For the present it will be necessary to forego any positive statements regarding either the age or the geologic sequence of this locality, but it is evident that the geology and fauna are both largely distinct in the North Fork region from those of the rest of the basin. GEOGRAPHIC DISTRIBUTION OF SPECIES. The majority of the specimens of Promerycochorus in the Marsh Collection bear accurate field labels, but there are a few of doubtful locality, although from the matrix, and from the letters of the field men, which state where |