OCR Text |
Show 1889.] SPECIES OF HYRACODONTOTHERIUM. 69 in the former the space occupied by the four premolars exceeds that between the canine and the anterior border of the first incisor by the whole width of the latter, in the present specimen the first of these dimensions only slightly exceeds the second. Again, whereas in the type species the first premolar is not longer (antero-posteriorly) than the canine, and is much shorter than pm- 3, in the present specimen the length of pm. 2 is much greater than that of the canine, and its difference from that of pm. 3 less than in the type. Further, there is a larger interval between ij_2 and ^3 in the specimen under consideration. These differences are indicated by the following measurements :- H. primcevum. H. filholi. Ant.-post. diam. of i^l °>006 °-011 Transverse „ „ 0,006 0,010 Ant.-post. diam. of canine 0,007 0,008 pm.l 0.0071 0,0095 pm. 2 0,009* 0,010 Length of space occupied by premolars . . 0,030 0,039 Interval between canine and anterior border of ij. 0,022 0,035 Length of outer narial border 0,023 0,038 Interval between i_2 and ±8 0,003 0,007 There is of course the possibility of these differences being sexual rather than specific, in which case the present specimen would be the male, and the increase in the first incisor would be analogous to that of the canine in the male Pig. In the absence, however, of any known instance, except in the case of the Elephant, of such a difference in the incisors of the two sexes, I am disposed, at least provisionally, to regard the present specimen as indicating a second species of the genus, which may be known by the name of H. filholi. The present specimen is important as showing that pm. 4 differs from that of Meniscotherium in having only a single outer lobe. "Whether the resemblance of the anterior portion of the skull of Hyracodontotherium to Hyrax indicates a genetic relationship between the two forms, the evidence at present available is insufficient to decide. It is, however, significant that both the Hyracoidea and the Condylarthra have such a similar type of carpus and tarsus that they are bracketed together by Prof. Cope in a single group. It may be added that the presence of an entepicondylar foramen in the humerus of Meniscotherium is in favour of Cope's reference of that genus to the Condylarthra rather than to the Perissodactyla. Finally, I have to thank Dr. H . Woodward for permission to bring the specimen forming the subject of this communication under the notice of the Society. 1 These dimensions are taken from Dr. Filhol's figure, and differ somewhat from those given in the text. |