1917] 



Stock: Structure of the Pes in Mylodon harlani 



277 



Ungual, Digit 2, Manus — 



Ungual, Digit 3, Pes — 



(Continued) 



(Continued) 



(5) Upper part of claw-process pre- 

 sents regular convexity from side to 

 side, flattened toward apex, and di- 

 vided by two sharp edges from less 

 convex under surface. 



(5) Claw-process convex above and 

 at the sides; under surface convex 

 transversely along its middle part, 

 concave on each side. Claw-process 

 for the extent of one inch and a half 

 from its apex is impressed above with 

 a shallow longitudinal groove. 



A comparison of the characters presented by the ungual, digit 3, 

 pes of M. harlani, with those above listed at once brings out a closer 

 agreement, especially in size, with the ungual, digit 2, manus, than 

 with the ungual, digit 3, pes, of M. robustus as interpreted by Owen. 



The conclusion, therefore, seems inevitable that in Owen's recon- 

 struction of the pes, as figured on plates 21 and 22 of the memoir on 

 Mylodon robustus, the second and third phalanges of digit 3 have 

 been interchanged with the corresponding phalanges of digit 2 of the 

 manus. So far as is known to the writer, Owen's interpretation of 

 these structures in Mylodon robustus lias never been questioned. 13 

 Rautenberg, 14 in a study of the greater part of a skeleton of 

 Pscudolestodon, describes and figures the pes and manus of that form. 

 Although he recognizes the terminal claw of the third digit of the 

 pes as the third largest of the ungual series, lie has not noted the 

 significance of this character when contrasted with M. robustus. In 

 comparing the feet of Pscudolestodon with M. robustus Rautenberg 15 

 states : 



Die Fussknochen bieten bei den beiden zum Vergleich herangezogenen Gravi- 

 graden nur geringe Abweichungen. Hervorzuheben ware, dass der Calcaneus 

 bei Mylodon etwas kiirzer imd weniger breit erscheint, und dass die zweite und 

 dritte Zehe bei Pseudolestodon nicht ganz die Grossenverhaltnisse des Mylodon 

 erreieht. 



Again, in comparing the manus Rautenberg"' writes as follows: 



. . . Ganz besonders in die Augen fallend ist die Grossenzunahme des zweiten 

 und dritten Fingers, dessen fast gleichlange Krallen die ubrigen inn das Drei- 



13 During the course of completion of this paper the writer learned from 

 Dr. W. D. Matthew that the changes necessitated by this new interpretation 

 were already made in the mount of Mylodon robustus in the American Museum 

 of Natural History. Mr. J. Z. Gilbert, who has studied the manus of Mylodon 

 harlani from Eancho La Brea, reaches the same conclusion (MS. in press) from 

 an interpretation of the second digit of the hand. 



14 Rautenberg, M., Ueber Pseudolestodon hexaspondylus, Palaeontographica, 

 Bd. 53, s. 1-50, 6 taf., 1906. 



15 Rautenberg, M., op. cit., p. 40. 

 i« Ibid., p. 41. 



