1900.] GRYPOTHERITJM (KEOMTLODON) 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- 

 tidae ; the presence of only four instead of five upper molars 

 separates it from the genera Mylodon, Lestodon, and Scelidotherium ; 

 the forward production of the nasals and the ossification of part of 

 the internarial septum place it definitely in the allied genus 

 Grypotherium, as originally diagnosed by Bernhardt. The only 

 question needing consideration is, whether the fragment of cranium 

 described by Owen in 1840 as the type of the genus Glossotherium* 

 is really identical with that subsequently described by Eeinhardt 

 under the name of Grypotherium darwini, as now seems to be 

 commonly believed. 



Darwin's original specimen, on which the genus Glossotherium 

 of Owen was founded, is preserved in the Museum of the Eoyal 

 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.) the 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 down- 

 wards 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 the 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 identical '". 



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 Both, only two species of Grypotherium^ 

 seem to be already known from the Pampa formation— G. darwini 

 by three skulls 3 and G. bonaerense solely by a maxilla 4 . 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 robusfus, Owen ' (1842), p. 154, footnote. 



3 Described respectively by Eeinhardt, Burmeister, and Lydekker, loc. at. 



4 F. Ameghino, ' Contribucion al Oonocimiento de los Mamiferos de la 

 Eepublica Argentina ' (1889), p. 738, pL xliv. fig. 8. 



