1918] Stock: The Pleistocene Fauna of Hawver Cave 



489 



amount of material preserved. Of the genus Nothrotherium two 

 individuals are known and this fonn is best represented in amount 

 of skeletal material. Much of the rolled and otherwise weathered 

 material belonging to the edentates seemingly pertains to this small 

 ground-sloth. Mylodon is known only by three specimens, a tooth 

 and two phalanges, while Megalonyx is questionably represented by 

 a single phalanx. It is a significant fact that in both Potter Creek 

 Cave and Samwel Cave, Nothrotherium and Megalonyx are the prin- 

 cipal representatives of the Gravigrada. The genus Mylodon is 

 conspicuous by its absence in these deposits. Again, from Mercer's 

 Cave near the town of Murphys, Calaveras County, California, Sin- 

 clair has described Megalonyx sierrcnsis. Thus we see that in the 

 cave accumulations of California, the megalonychid ground-sloths are 

 by far the more important types present, while the mylodonts occur 

 but rarely. 



In contrast to the ossiferous accumulations in caves are those 

 deposits containing remains of a typical plains fauna, or, at any rate, 

 an assemblage in which the larger herbivores, usually associated with 

 extensive stretches of level or rolling country, predominate. At 

 Rancho La Brea, for example, the mylodont sloths greatly overshadow 

 in numbers both Nothrotherium and Megalonyx. Nothrotherium 

 occurs at that locality more abundantly than does Megalonyx. Thus 

 the relation between mylodonts and megalonychids, so far as actual 

 numbers are concerned, is exactly the reverse of that obtaining in the 

 cave deposits. Again, in the Pleistocene fauna of the Fossil Lake 

 Beds of eastern Oregon a number of forms are included, such as horses, 

 camels and antelopes, which are to be associated with extensive open 

 stretches of country. In this fauna Mylodon sodalis (Mylodon har- 

 lani?) occurs, but the megalonychid sloths are entirely absent. 



MYLODON HAELANI Owen 



Three specimens indicating the presence of mylodont sloths so 

 closely resemble corresponding elements of Mylodon harlani from 

 Rancho La Brea that they are determined as pertaining to this genus 

 and species. 



The cross-section of the first inferior tooth, no. 19891, from Haw- 

 ver Cave, is almost identical with that of Mylodon harlani Owen as 

 figured by Leidy. Actual measurements show, however, that the cave 

 specimen is smaller in anteroposterior diameter and larger in trans- 

 verse diameter. Unfortunately the first tooth in the type specimen 

 is fragmentary and comparison is limited to the outline of the tooth. 



