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Show 1886.] MR. R. LYDEKKER ON SCELIDOTHERIUM. 497 the nasals themselves are more pointed posteriorly and wider anteriorly, the width of the anterior expansion being greater than that at the frontal expansion, while the reverse condition obtains in 8. brongniarti. The resemblance between the two crania is, however, sufficiently close to render it probable that the two forms were closely allied, and that the premaxillae of the present form were similarly aborted. The dimensions of the present form are as follows : - Length of the facial portion of maxilla 0*122 Width of the two occipital condyles 0*099 Length from condyles to last tooth 0*238 Length of upper dental series 0*093 Length of mandibular symphysis 0*124 Interval between hinder border of symphysis and first tooth 0*012 Since the present form is decidedly distinct from all the species mentioned above, and since I cannot identify it with either of the other ill-defined forms referred to Scelidotherium and Platyonyx, I can only adopt the course followed in the case of the preceding species; and I accordingly propose to designate this form as Scelidotherium chiliense, since I shall immediately show that the genus Platyonyx ought to be merged in Scelidotherium. Platyonyx is stated by Lund (and his view is followed by Dr. Burmeister1) to be distinguished from Scelidotherium by the absence of an entepicondylar foramen to the humerus, and by the more flattened phalangeals; while, according to Messrs. H. Gervais and Ameghino2, the crochet of the last lower tooth is more prominent. Sir R. Owen3, who unites the two genera, is of opinion that the limb-bones referred by Lund to Platyonyx really belong to Glyptodon, I have no means of deciding which of these two views is correct; but the close general resemblance in the structure of the nasals of Scelidotherium chiliense to those of the so-called Platyonyx brongniarti leads m e to conclude that whether the humerus of the latter was, or was not, provided with an entepicondylar foramen, the species is not entitled to generic distinction from Scelidotherium, the alleged differences in the structure of the phalangeals and of the last lower tooth being characters which are certainly not more than specific ones. Taking the three species, S. leptocephalum, S. bravardi, and S. chiliense together, it will be seen that they form a sequence as here placed in regard to the length of the nasals-S. chiliense (together with S. brongniarti) being the least, and 8. leptocephalum the most removed from the type of cranium obtaining in Mega-tficpfutyii Affinities of the Genus. In conclusion, I may observe that Scelidotherium appears to be a 1 Monatsb. k. preuss. Ak. Wiss. 1881, pp. 374-380. 2 ' Mammiferes fossiles de TAmerique meridionale,' p. 151 (1880). 3 Memoir on the Mylodon, p. 170, note. PROC. ZOOL. Soc-1886, No. XXXIII. 33 |