| OCR Text |
Show 250 MR. ST. GEORGE MIVART ON INDRIS DIADEMA. [Mar. 14, in 7. laniger, the third cusp of the external cingulum being more developed than in the first upper molar. The third upper molar is relatively smaller than in either of the other genera of Lndrisinee. It has indeed two anterior cusps, one external, and the other internal; but these are much smaller than are the principal cusps of the more anterior molars. Behind these the posterior part of the tooth has a slightly irregular surface and margin, but is without any distinct cusps. The inferior incisors and canines are quite like those of 7. laniger, except that the inner surface of each canine has a wider groove than even in 7. brevicaudatus, owing to the greater development of the lateral external prolongation of the basal cingulum. Fig. 2. Inside of left half of mandible. Scale, nat. size. The anterior lower premolar is very much like that of 7. laniger, but is more vertically and less antero-posteriorly extended than even in 7. brevicaudatus. The posterior lower premolar is quite like that of 7. laniger, except that the median longitudinal ridge does not extend upwards as far as the external margin of the tooth does, though it does so rather more than in the short-tailed form. The first lower molar is distinctly quinquecuspidate, the two processes of the antero-external cusp of 7. laniger being here distinct cusps. In other respects it quite resembles its homologue in that species. The same is the case, at least sometimes, in 7. brevicaudatus. This tooth has a great resemblance to the lower molars of many insectivora, the three anterior cusps together forming a triangular prism with one angle turned outwards; while the postero-internal angle of the prism is connected by a ridge with the molar's posteroexternal cusp. The second molar resembles the first, except that there are but four cusps (the most anterior of the three internal ones of the first molar aborting), that the antero-internal cusp is more vertically extended, and the antero-external one less so, and finally that (as in 7. laniger) the anterior half of the tooth is not narrower transverselv than is its posterior half. The third and last lower molar is like that of 7. brevicaudatus, and has its supplemental fifth (posterior) cusp rather more developed than it is in 7. laniger. |
