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Show 1900.] GRYPOTHERIUM (NEOMYLODON) LlSTAI. 73 Generic and Specific Determination. The fortunate discovery of all parts of the skull and dentition renders the generic determination of this Ground-Sloth now quite certain. The teeth show that it belongs to the family Mylodon-tidse ; the presence of only four instead of five upper molars separates it from the genera Mylodon, Lestodon, and Scelidotherium; the forward production of the na?als and the ossification of part of the internarial septum place it definitely in the allied genus Grypotherium, as originally diagnosed by Reinhardt. The only question needing consideration is, whether the fragment of cranium described by O w e n in 1840 as the type of the genus Glossotherium1 is really identical with that subsequently described by Reinhardt under the name of Grypotherium darwini, as now seems to be commonly believed. Darwin's original specimen, on which the genus Glossotherium of O w e n was founded, is preserved in the Museum of the Royal College of Surgeons. It has thus been possible to compare it directly with the undoubted cranium of Grypotherium from the Patagonian cavern. The specimen is merely the left half of the hinder part of the cranium, and is therefore very inadequate for discussion ; but several features seem worthy of note. Compared with the new skull no. 1, the fragment named Glossotherium has (i.) tbe inner wall of the temporal fossa less flattened, (ii.) the digastric fossa deeper in proportion to its width, (iii.) the hinder border of the inflated pterygoid vertical, instead of sloping downwards and forwards, (iv.) a much larger and deeper pit for the articulation of the stylohyal, and (v.) a longer canal penetrating the base of the occipital condyle for the passage of tbe hypoglossal nerve. In all these respects the so-called Glossotherium agrees much more closely with the typical Mylodon; and Owen was probably correct in 1842 when he expressed the opinion that the two are at least generically identical2. I am therefore of opinion that Grypotherium is the correct generic name for the Ground-Sloth from the Patagonian cavern, while Glossotherium must be relegated to the synonymy of Mylodon. The specific determination of the new specimens is more difficult. As remarked by Roth, only two species of Grypotherium seem to be already known from the Pampa formation-G. darwini by three skulls3 and G. bonaerense solely by a maxilla4. The portions of skull and dentition now under discussion indicate an animal much larger than G. bonaerense (assuming the original maxilla to be that of an adult): while they are considerably 1 E. Owen, ' The Zoology of the Voyage of H.M.S. Beagle.-Part I. Fossil Mammalia' (1840), p. 57, pi. xvi. 2 E. Owen, 'Description of the Skeleton of an Extinct Gigantic Sloth, Mylodon robustus, Owen ' (1842), p. 154, footnote. 8 Described respectively by Bernhardt, Burmeister, and Lydekker, loc. cit. 4 F. Ameghino, ' Contribution al Conocimiento de los Mainiferos de la Bepublica Argentina : (1889), p. 738, pi. xliv. fig. 8. |
