RODENTS 215 



embracing the occipital and basal parts of the cranium, including the 

 foramen magnum. These all show the usual stain and the usual Aftonian 

 phase of fossilization. 



In addition to the Aftonian specimens noted above, there are probos- 

 cidean bones from gravels belonging possibly to other horizons. Within 

 the year there has been received an imperfect ilium, but with the acetab- 

 ulum complete, from Le Mars ; the lower end of a scapula, with glenoid 

 fossa and part of the acromion spine, from Lake View, and a large, fairly 

 perfect atlas comes from gravels at Eock Eapids. These are not silicified 

 to the same extent as fossils from the Aftonian, and it is probable they 

 represent faunas of later stages. About 1876 a complete skeleton of Mas- 

 todon americanus was found near Adel, in Dallas County, imbedded in 

 peat that partly filled a "kettle" in the surface of the Wisconsin drift. 

 This fact may be cited as part of Iowa's contribution to the great volume 

 of evidence that the mastodon was here in post-Glacial time, and may 

 have been present during each of the post-Aftonian interglacial stages. 



EODENTS 



The great Pleistocene beaver, Castoroides, is represented by a part of 

 an incisor from the Elliott pit at Turin, Iowa, and a molar from the 

 Collins pit, near Sioux Falls, South Dakota. In 1907 a nearly perfect 

 incisor (plate 23) was found in sand pumped from the Nishnabotna 

 Eiver, near Oakland, Iowa. There is fairly clear evidence that the sand 

 of the Nishnabotna Valley is Aftonian. It occurs in a region that was 

 not reached by the streams which deposited the younger sands and gravels. 



Edentates 



Additions to our knowledge of the Aftonian ground sloths are limited 

 to a few parts of the skeleton of Megalonyx. There is a patella from the 

 Anderson pit at Sioux City, a right radius (plate 24) from the Elliott pit 

 at Turin, and a right tibia from the Cox pit at Missouri Valley. . The 

 radius is complete and unabraded, and, except that it is a trifle smaller, it 

 agrees almost perfectly with Leidy's figures and descriptions of the radius 

 of Megalonyx jeffersoni.^ The ulnar articular facet is more nearly circular 

 than in the specimen described by Leidy, if judgment may be based on the 

 descriptive term "demi-circular," which is applied to this feature of the 

 bone in the text. The bicipital tuberosity is somewhat more prominent 

 in ours than in Leidy's specimen, and the rugosities of the anterior sur- 

 face are more pronounced. In all essential particulars, however, the cor- 



« A memoir on the extinct sloth tribe of North America, by Joseph Leidy, M. D., p. 27 

 et seq. Illustrations of the left radius are given on plate Ix, figure 5, and plate x, 

 figure 1. 



