OCR Text |
Show 127 ceases. The second molar has the anterior portion elevated, supporting three cusps and a large heel, with lateral and sub- median cutting edges. The last molar is smaller, elongate, oval, and two- rooted, with marginal posterior, intennarginal external, and two anterior tubercles, of which the inner is bifid. The ramns is slender, and the symphysis elongate. The angle is not incurved. First premolars one- rooted. Measurements. M. Length of dental series 0680 Length of four premolars 0340 Length of first molar 0105 Length of second molar 0100 Width of second molar 0055 Length of third molar 0080 Width of third molar in front 0040 Depth of ramus at third premolar 0130 Depth of ramus at last molar .0150 AtlJGATOK CHAMENS18, $ p. flOV. Represented by portions of the mandibular arch of a small crocodilian resembling in some respects the A. heterodon of the Wyoming beds. The posterior teeth have the same short, expanded, sessile, bean- shaped crowns, with a median longitudinal ridge, and more delicate lin^ s radiating close together from it to the border of the crown. The anterior teeth differ in being cylindric instead of compressed. There is a large canine preceded and followed by teeth of much smaller size. Measurements. M. Length of symphysis 019 Length of alveoli of six teeth from symphysis 022 Width of ramus just behind symphysis 010 Long diameter of posterior tooth 005 The specimens selected as type is one of the smallest. The surface of the bones is ronghened with pits. PLASTOMENUS LACHKYMALIS, « p. not. The largest species of the genus, and abnndantly represented in the Eocene of New Mexico. The costal bones are rather finely puncrate, the posterior as well as the anterior. The anterior costal bones are crossed by numerous ridges from side to side obliquely ; the obliquity increasing posteriorly. On the posterior bones, they are broken into vertical bars, separated by considerable intervals, and of linear form. The posterior costals reach a thickness of 0m. 006 and a width of 0m. 025. The pitting of the posterior part of the carapace distinguishes this species from the P. ( edemius. PART II. In addition to the investigations pursued in the regions already indicated, and of which some of the new species have been described, it may be stated that a careful examination was made of the extensive lacustrine deposits in the valley of the Rio Grande. These deposits are supposed to commence to the northward of Taos, N. Mex., and continue to an unknown distance southward, certainly at least fifty miles beyond Santa Fe\ and occupy that portion of the valley between the Rocky Mountains in the east and the Jemez range in the west, and have been stated as late Tertiary, but without special determination or co- ordination with the other known lacustrine formations of this continent.* Abundant material having been obtained by the party, it is easy to determine the fauna, whose remains are entombed in it, to be a part of that already described by Dr. Leidy and the writer as occurring in Dakota and Colorado under the name of Pliocene. This conclusion is indicated by the presence of the genera Hippotherium, Protohippus, Procamelus, Coeoryx, and Merychippus, and known Pliocene species of other genera, among which may be mentioned Canie, Aceraiherium, & c. In addition to species already known, a number new to science were obtained, of some of which descriptions axe here given. MAfcTEfi NAM BI ANUS, 8p. JtOV. Represented by a mandibular ramus, which supports three teeth. The anterior blade of the sectorial is rather obtuse. • The new species described from the valley of the Rio Grande were discovered from August 20 to September 1,1874. |