EDENTATA 353 



ference from its great size that it belonged to the imperial mammoth, a 

 tooth of which (plate 24) comes from the same gravel pit. 



Edentata 



megalonyx 



Some years ago Todd called attention to beds of sand and gravel below 

 drift in southwestern Iowa. A paper on the subject was read before the 

 American Association in 1889, 13 and the abstract states that "a large claw 

 of some gigantic mammal was shown, which was obtained from Mills 

 county, Iowa, in the sand below the drift." A footnote referring to the 

 specimen says that "this has been determined by Professor Leidy to be a 

 claw of a Megalonyx." The "sand below the drift" in Mills, as in all 

 the other counties of western Iowa, is interglacial. It lies below the Kan- 

 san drift, but there is another sheet of drift, the pre-Kansan, below it. 

 On the basis of Leidy's determination, however, the Megalonyx may be 

 accepted as a part of the Aftonian mammalian fauna. 



MYLODON 



From the noted Cox pit at Missouri Valley there comes an imperfect 

 terminal phalanx of Mylodon (plate 26). The tip of the ungual process 

 is broken off ; otherwise it is practically complete and shows the character- 

 istics of this part of Mylodon very clearly. The claw as a whole is pro- 

 portionately much thicker, is less falcate, and tapers less rapidly toward 

 the point than do the claws of Megalonyx. The ungual process is regu- 

 larly rounded on the upper side instead of being compressed to a rela- 

 tively sharp ridge. All the characteristics coincide with Owen's classical 

 description of the distal phalanges of Mylodon. 14 



Correlation 



The Aftonian fauna is as yet very incomplete. Additions to the list of 

 species must wait on the further development of the sand pits and gravel 

 beds. Besides the sloths, the forms thus far discovered and recognized 

 are all large herbivores. An attempt to correlate the Aftonian beds with 

 Pleistocene faunal zones which have been established in regions lying out- 



13 J. E. Todd : Evidence that lake Cheyenne continued till the Ice age. Proceedings of 

 the American Association for the Advancement of Science, vol. xxxvii, 1889, pp. 202-293. 



"Richard Owen: Description of the skeleton of an extinct gigantic sloth. Mylodon 

 robustus Owen, pp. 94, 95, 107, 122. Leidy's work, A memoir on the extinct sloth trihe 

 of North America. Smithsonian Contributions to Knowledge, accepted for publication 

 December, 1853, p. 37, describes the ungual phalanges of Megalonyx. The plates in 

 both of these publications assist in making clear the differences between the claws of the 

 two great sloths mentioned. 



