HELALETES, Marsh.
Am. Journ. Sc. and Arts, 1872, p. 218.
Additional material enables us to give further characteristics of this genus, which may be thus defined: Mammals, allied to Lophiodon, having a third lobe to the last lower molar, short symphysis, and with the teeth of the lower jaw forming a continuous series. Astragalus has narrow, oblique condyles.
| Dental formula: I. | ? - ? | , C | 1 - 1 | , Pm. | 4 - 4 | , M. | 3 - 3 |
| 3 - 3 | 1 - 1 | 4 - 4 | 3 - 3 |
Synopsis of Species.
| A. | Teeth small; a small tubercle on the outer margin, between the cusps of last upper molar | H. boöps. |
| B. | Teeth much larger and proportionately broader; no tubercle on last upper molar | H. latidens. |
Helaletes latidens, sp. nov.
Lower Jaw.—The ramus is stout, and resembles in general form that of Hyrachyus, but the alveolar border is straighter than in that genus; the ascending portion forms a right angle with the horizontal portion, and the masseteric fossa is deep. The symphysis is comparatively short, and there is complete bony union between the rami, which do not diverge so much as in Hyrachyus. As in that genus, there are several small mental foramina beneath the premolar series. The dental series forms a nearly continuous line, the only diastema being a very short one between the first and second premolars. The incisors have compressed fangs, and are arranged in a slight curve. The canine is small and subcircular at base. The premolars also are small; they somewhat resemble those of Hyrachyus in shape, but are smaller, and have the posterior lobe not so well developed. The first is implanted by a single fang, the others by two. The molars (except the last) consist of two pyramidal lobes, which form transverse cutting-crests, as in Tapirus and Hyrachyus. The basal ridge is shown on the anterior and internal sides only. Externally the lobes meet at their bases, inclosing the valley on that side. The last molar is by far the longest of the series, and consists of three lobes, of which the anterior is the largest, and the posterior the smallest. The basal ridge at the anterior part of the tooth is very strongly marked.
Upper Jaw.—The molars increase in size from first to last with considerable regularity. The premolars are small, and, as in Hyrachyus, have one single internal cone, which is joined by transverse ridges from the two outer cusps; the anterior accessory tubercle is well developed. The first molar is considerably larger than the last premolar; it is much worn, and does not show anything more than that there are two internal cones. The anterior conical buttress is very largely developed throughout the true molar series. The second and third molars resemble almost precisely the corresponding teeth of Hyrachyus. Their shape, however, is more nearly square than is usual in that genus.