OCR Text |
Show 119 ternal as well as the external enamel- face, and the former possesses a longitudinal angle bounding its concavity. The grinding- face of the molars and some of the premolars is ao - shaped as in the other species, but the anterior limb of the figure is much thickened on the inner face, so as to have a triangular form, the base being inward. This base is notched by a second groove of that side of the tooth, which interruption is obliterated by prolonged attrition. This portion of the crown is elevated above the posterior, in consequence of the more rapid removal of the latter by trituration. The large internal and external grooves continne nearly to the base of the crown, as in the larger species. The last inferior molar is longer than the others, and is three- lobed, forming by its base nearly an isoceles triangle. The heel is formed by the backward production of the posterior convexity of the OQ , the central line of the figure forming » diagonal ridge across the middle of the tooth. The mandibular ramus is of a deep compressed form. Measurements. M. Length of three consecutive molars 0250 Length of last two molars 0210 Length of penultimate molar 00S4 Width of penultimate molar 0062 Length of last molar. 0112 Width of last molar 0070 Length of incisor, second form 0260 Diameter of incisor, second form 0050 Diameter of incisor, first form, transverse 0030 Diameter of incisor, first form, anteroposterior 0070 E8THONYX BURMEI8TERII, sp. ftOV. A species more nearly allied to the E. bisulcalus than to the type of the genus is represented by a portion of the right mandibular ramus, with the last molar tooth in perfect preservation. While the jaw is of depth similar to that of the E. bisulcatus, it is more slender in its proportions. The molar, also, while of nearly the same length, is relatively narrower, especially in its anterior portion. The crown of this tooth is worn in the specimen, and the anterior portion is elevated above the posterior, and displays . a trace of the notch of the inner margin already observed in the species last described. The composition of the tooth is similar in other respects. No ciugular; enamel smooth. Measurements. M. Length of last lower molar 009 Length of last lower molar from anterior tubercles 0060 w:,) ti> S anteriorly 0050 W l c U n $ posteriorly 0025 Depth of ramus at last molar 0240 This species is dedicated to Prof. Hermann Burmeister, director of the museum of Buenos Ayres, who has studied the group of Toxodontidce, and given us an excellent account of their osteology. ESTHONYX ACER, Sp. 710V. Char, specif.- Established on a portion of the lower jaw, in which the last four premolars remain. Tbey resemble those of the species already named, except in the anterior one of the series. This tooth in E. acer assumes the form of a premolar, the posterior V becoming a curved median cutting edge, and the anterior V opening into a crescentoid section ; it rises to an acuminate apex, having thus a rather sectorial character. In the last three molars, there is a small tubercle at the inner base of the posterior limb of the anterior V. Posterior Vmuch lower; enamel smooth. Measurements. Length of four last molars 035 Length of three last molars 026 Length of penultimate molars 008 Width of penultimate molare 005 Length of last molar 011 Width of last molar 005 Depth of jaw at last molar 020 This species differs from the E. bimhatus in the modified form of tbe last premolar; in the latter, it is relatively larger and more like the true molars. The last molar of E. acer is more like that of* the E. burmeisterii, but the mandibular ramus of that species is relatively much deeper and similar to that of E. bisuloatus. |