The dentition. The superior incisors are larger than the corresponding teeth in Elasmognathus bairdii. The inferior incisors are slightly smaller than the superior. Both series have the crowns somewhat cupped, especially so in the superior incisors. The first and second inferior incisors are of equal size, while the third is two-thirds as large as those preceding it. The crowns of both canines are broken off, but the diameters of their roots, measured on the alveolar borders, are greater than the corresponding parts of the larger incisors. A long diastema succeeds the canines. The premolars have their anterior cusps united into transverse ridges, slightly notched at the summit. In all

FIG. I.

except the second premolar, the ridges are perpendicular to the long axis of the jaw. They are equally developed on the third and fourth premolars. Posterior cross crests are not developed on any of the premolars. In the second premolar, the protoconid is larger than the deuteroconid and is situated farther forward than the latter. In the succeeding premolars, these cusps are of the same size and are situated directly opposite each other. The tetartoconid of the premolars is smaller than the metaconid. The latter cusp is united with the inner side of the base of the protoconid by a ridge. This structure is also found in the molars, all of which have two cross crests. The posterior crest in the first and second molars is somewhat oblique to the axis of the jaw. The third molar is too imperfectly preserved to describe. Anterior and posterior cingula are present on all the molars and premolars. Traces of an external cingulum are found at the outer end of the transverse valley in all except the second premolar. In this tooth the paraconid is very large, uniting by a ridge with the protoconid. In the remaining premolars the paraconid is replaced by a style rising but little above the level of the anterior cingulum.

The jaw. The inferior border of the jaw is parallel with the alveolar border. The symphysial portion rises at a low angle, much less than in the tapir. The flatness of this angle is perhaps due in part to a slight amount of crushing which the specimen has sustained. The posterior border of the mental foramen is directly below the anterior border of the second premolar.

The fore limb.-The humerus and radius have about the same shape as in the tapir. The deltoid ridge of the former is broken off, so that it is impossible to say whether it was hooked or not. The shaft of the radius is more strongly curved than the corresponding element in Protapirus validus as figured by Hatcher,' but a part of the curvature may be due to distortion. The carpus does not call for special description, not differing materially from that of Protapirus obliquidens. W. & E. The anterior contact of the lunar and magnum is still small, as in the White River species. There were four digits in the manus, the length of metacarpals III, IV, and V being about the same as in E. bairdii, but less robust. In shape they correspond closely with the metacarpals of the latter, except that the proximal portion of the fifth is inclined at a greater angle to the shaft of the bone than in the living form. The phalanges, which are of the second row, are shorter and less robust than those of the tapir.

Phylogenetic position.—The remains just described indicate an animal much larger than any of the White River species of the same genus. The structure of the molars and premolars suggests Protapirus validus as a probable ancestor. There are, however, several differences. In addition to the considerable difference in size, the third premolar of P. robustus has the anterior cross crest vertical to the long axis of the jaw, while in P. validus it is somewhat oblique. The diastema, as in P. validus, is shorter than in Elasmognathus, while the mental foramen has moved. slightly posterior to the position it occupies in the White River ancestor. Gradations between the two types probably occur among the as yet unknown tapirs of the Lower and Middle John Day.

1 Loc. cit., p. 167, Fig. 1.

In this connection, may be mentioned a second specimen, (No. M 1525 University of California Pal. Museum), representing probably another new species, obtained by the writer in the uppermost beds of the John Day system, on Johnson Creek, Grant county, Oregon. The horizon is considerably higher than that from which Protapirus robustus was obtained, and appears to be faunally distinct. It is characterized by the remains of numerous individuals of a camel belonging to the genus Protomeryx and by a rodent generically new. The tapir remains are of a young animal and are not complete enough to characterize specifically. They comprise fragments of a jaw with which three incisors and the second inferior premolar are preserved. The two large incisors, apparently the inferior median pair, are two-thirds as large as the corresponding teeth in P. robustus. They are spatulate in shape and slightly cupped. The anterior face is marked by delicate growth lines. The third incisor is an exceedingly small tooth with the crown 31 mm broad. Imperfect preservation of the symphysial region renders it impossible to make any statement regarding the canine. The second premolar of the right side is the only one of the cheek teeth perfectly preserved. This tooth is entirely unworn, and was just appearing through the gums at the time of the animal's death. In this tooth, the tetartoconid is much larger than in P. robustus and the junction of the metaconid with the tetartoconid is much more complete, forming a cross crest but slightly notched. A ridge

joins the former cusp with the middle of the anterior cross crest. The protoconid is considerably anterior to the deuteroconid and as in P. robustus is united with the paraconid by a ridge. The anterior cross crest is sharply notched, but this structure would probably assume the character of the anterior cross crest in P. robustus with the wearing down of the deuterocone by use. External cingula appear at the outer margin of the median valley and on the external side of the paraconid. A posterior cingulum is also developed.

MEASUREMENTS

Width of the crown of first inferior incisor

Width of the crown of third inferior incisor

Length of the first premolar crown, antero-posteriorly.

PALEONTOLOGICAL LABORATORY,
University of California.

WM. J. SINCLAIR.

THE FORMATION AS THE BASIS FOR GEOLOGIC

MAPPING

In a recent number of this JOURNAL Mr. Bailey Willis, in a paper on "Individuals of Stratigraphic Classification," has restated and rediscussed the problem which must be solved before cartographic work of any magnitude can be planned. This problem involves a careful consideration of the relative weights to be assigned, in any system of classification to be used on geologic maps, to faunal, lithologic, and chronologic (successional) characters. Mr. Willis discusses the question in its various aspects, and his final decision is that the lithologic unit (formation) is best adapted to the requirements of the cartographer.

While agreeing, in the main, with the conclusions reached by Mr. Willis, it seems desirable to call attention to certain arguments, not specifically mentioned by him, which may be adduced in support of those conclusions; and, further, to examine the results of the application of the proposed system of classification to some particular cases of interest.

Before commencing the discussion of this question I wish to acknowledge my indebtedness to Dr. F. J. H. Merrill, director of the New York State Museum, who has greatly aided me, with both criticism and advice, during the preparation of this paper.

THE NECESSITY FOR UNIFORMITY

Though the formation, defined primarily by lithologic characters, was officially adopted in 1889 as the cartographic unit of the United States Geological Survey, in practice it has not entirely superseded other units of classification. Great variety exists in the practice of the various state geological surveys, as is indicated by their official maps; and greater variety, as might indeed be expected, in unofficial maps accompanying papers on