168 MATTHEW— RECENT DISCOVERIES OF 



Edentates. — The edentates are all ground sloths related to Mega- 

 lonyx, but belong to four distinct genera. The largest and most 

 abundant is Megalocnus, about the size of a black bear. The tusks 

 are flattened into a meniscus cross-section, and set near together, 

 especially in the lower jaw, so that it has a curiously rodent-like 

 effect. The cheek teeth are exceptionally long, and in consequence 

 the palate is depressed below the level of the cranium, and the jaw 

 extremely deep. This is like the gigantic Megatherium, but the 

 form of the cheek teeth is almost exactly as in Megalonyx. De- 

 tailed comparisons show that the Cuban genus is most nearly related 

 throughout to Megalonyx. 



Mesocnus is a smaller and more primitive genus, which is about 

 the size of the Miocene ground sloths of Patagonia, and like them 

 has a long tongue of bone projecting forward between the tusks. 

 The cheek teeth are not so long in this genus, but they have almost 

 the same form as in Megalocnus or Megalonyx, different from the 

 more primitive form of the cheek teeth in all the Miocene Mega- 

 lonychidse. The tusks are rather small and not so broad or menis- 

 coid in section as in Megalocnus. On the whole this is a more 

 primitive genus, except the humerus, which has lost the entepicon- 

 dylar foramen, as in Megalonyx. 



Miocnus is of about the same size as M^.jocn«.y but quite distinct. 

 It is very closely related to Acratocnus of Porto Rico, perhaps the 

 same genus. It has a short wide jaw and stout triangular tusks 

 with a short, bony tongue between. 



Microcnus is the fourth genus of ground sloths, an animal about 

 the size of a cat, smaller than the living two-toed sloth. It resem- 

 bles Megalocnus in the form and position of the tusks, but the 

 molars are not so long-crowned and differ considerably in form, 

 with a marked suggestion of the square cross-section of the INIega- 

 theriidcC. I have not seen the skull or upper teeth ; a couple of foot 

 bones doubtfully referred to this genus come nearer to the living 

 tree-sloths in proportions than they do to any of the large ground- 

 sloths. It would be very interesting to know more about this little 

 animal. 



There is so much individual and age variation in ground sloths 

 that it is difficult to say how many species of these genera are prcs- 



