OCR Text |
Show 72 besides tb. 3 species mentioned, tbe Rhinoceros crass us, Leidy, aud the A, Jemezanus, first described below. These are, however, orfly referred to it provisionally, as the number of the premolar teeth is not yet known in either. The known species have only been found in the beds of the Loap Fork epoch. Tbe A. meridian** was established by a superior molar tooth from Texas. The corresponding molar in the New Mexican species does not differ from it. The general characteristics of this almost unknown species may then be learned from onr specimens. In general features it much resembles tbe A. megalodus, but there are numerous differences. There is a considerable protuberance of the anterior border of the posterior transverse crest, nearer the outer border of the crown than the protuberance of the posterior border of the anterior transverse crest. These give the transverse valley a sigmoid form, which is not seen in A. megalodus. There is no posterior protuberance of the anterior transverse crest of the last superior molar. There is a strong anterior basal cingulnm on the true molars, and a very strong elevated cingulum connecting the inner ends of the transverse crests. No external cingula. The mandible differs from that of A. megalodus in the contracted form of the symphysis, aud the small size of the outer tusk- like incisors, which are scarcely half as large as those of the former; but it is possible that this character is sexual. As compared with five mandibles of A. megalodus, the last molar originates closer to the base of the coronoid process; in the latter there is a considerable interval in frontTof tbe ascending process. The form of the dentary bone is that of A. megalodus, and not thick and massive as in A. crassus, Aphelops Jemezanus, Cope, sp. nov. That a second species of rhinoceros even larger than the other species of Aphelops formerly existed in the region of New Mexico is demonstrated by a right mandibular ramus obtained by Dr. II. C. Yarrow from near the town of Santa Clara, on the west side of the Rio Grande. The specimen in its present condition includes the condyle, angle, and ramus as far as the last premolar, and supports the three true molars. The latter are worn, indicating tbe full age of the animal. They still retain the enamel surface of the sinus between the posterior and median transverse crests, and the lower end of the sharp inner margin of the anterior transverse crest. While the ramus exhibits the compressed form seen in A. megalodus and A. meridianus, it differs from these and the A. crassus in many striking respects. Thus the inferior margin near the angle does not exhibit the protuberance and following contraction of the inner side seen in the first two species. In another feature it differs from all the other species, i. ?., in the form of the ascending ramus. This rises very gradually from the basis of tbe last molar, leaving a subhorizoutal edentulous space behind the latter as long as the second true molar; its anterior face, instead of being flat and bounded by strong lateral angular ridges, as is the case in A. crassus and the two other species, is rather narrowly convex. Instead of the usual ridge of the outer side, the anterior border of the area of insertion of the masseter muscle is marked by a prominent carved protuberant margin, which is wanting in the three other species; the surface in them being plane. Behind tbe condyle is seen the tuberosity characteristic of the Rhino-ceridie. The internal pterygoid fossa is well marked. Rugosities for insertion of the lower border of the masseter muscle are strong. The relations of the dentition of this species are also peculiar. The last molar is nearly half as large again as that of specimens of A. megalodus and A. meridian us of similar dimensions of ramus, and the teeth diminish in length anteriorly more rapidly than in width. Thus while the first true molar is as long as in the two species named, the width is between one- half aud one-third greater. There are no external nor internal basal cingula. Measurements. M. Length of ramus from fourth premolar ( behind) to middle of masseteric fossa 240 Length of series of true molars 144 Length of first true molar... 044 Width of first true molar 033 Length of third true molar .. .058 Width of third true molar 035 Diameter of ramus at first molar 080 Depth of ramus at third molar 093 PRODOSCIDEA. Mastodon productusf Cope, Proceedings of the Philadelphia Academy, 1874, p. 2* 21. Fragments of the skeletons of this species are quite abundant in the Santa Fe* marls, and, as it is the most striking species of the ancient fauna, was the first to become known. The dentition of both jaws was obtained. It belongs to the typical mastodons, and is nearly related to the M, yngustidene and M, longirostris of Southern Europe, |