Mylodon harlani, from Bock Greek, Texas. 385 



materials are still lacking to give us any real knowledge of the 

 suborder in that or the more ancient stages." 



The map which has been compiled (fig. 16) indicates no 

 fewer than sixteen distinct localities wherein remains of the 

 genus Mylodon have been found in North America, while the 

 arrow points to the probable migratory route during early 

 Pleistocene or late Pliocene time. Mexico should give evidence 

 of this migration, but except for the questionable Austin Co. 

 occurrence I am at present unaware of the discovery of Mylo- 

 don south of the Texas panhandle. 



The northernmost limit of distribution coincides with the 

 southern extent of maximum glaciation, two localities, the 

 Port Kennedy bone cave and Big Bone Lick, being right on 

 the line of demarcation ; while Seneca, Kansas, Tecumseh, 

 Nebraska, and Harrison Co., Iowa, are within the limits of the 

 ice. In Oregon the localities follow the outline of the project- 

 ing glacial spur most curiously. This northern limit of distri- 

 bution is open to two interpretations, one, that of a climatic 

 limit for warmth-loving beasts, being the first to be suggested 

 by the map. On the other hand, the genus may well have had 

 a more northerly limit during a warm interglacial period, their 

 remains being destroyed by the subsequent advance of the ice. 

 This is the only explanation in my mind for the distribution in 

 Oregon, while in the Kansas locality, actually within the limits 

 of glaciation, the specimen came from a well, implying a depth 

 sufficient to guard the remains from destruction. 



The Texas Mylodon is associated with warm climate animals 

 — horse, elephant, camel, peccary and Glyptodon — representing 

 what Osborn calls the first Pleistocene fauna. The Seneca, 

 Tecumseh, and Iowa Mylodons lay within the limits of the Kan- 

 san drift* and as they were buried deep within it the assumption 

 is that the genus lived not later than the Aftonian interglacial 

 period which preceded the Kansan glacial period at the very 

 beginning of Pleistocene time. The Texan fauna embraces 

 several Aftonian forms as given by Calvin, f which include 

 Mylodon. On the other hand, Calvin's list contains some 

 forms which apparently had not yet put in their appearance in 

 Texas, as, for instance, Mammut americanam, but this may 

 be due to geographical and environmental rather than to time 

 distinction. This evidence serves to check the inference 

 derived from the specimens found within the limits of the ice. 



*See Hay, 0. P., Smithson. Misc. Coll., vol. lix, No. 20, fig. 7 on p. 9. 

 1912. 



f Calvin, S. E., Iowa Geol. Surv.. vol. xx, p. 316, 1910. 



