40 EXTINCT AND VANISHING MAMMALS 



in greatest length. Three calcanea are essentially similar to 

 the calcaneum of Mylodon. 



While Acratocnus and Parocnus did not perhaps become ex- 

 tinct till fairly recent times, possibly not until after the dis- 

 covery of the West Indies by Europeans, the Cuban ground 

 sloths may have died out at an earlier time. Their remains are 

 known in some abundance in deposits around a warm spring 

 at Ciego Montero, associated with bones of a crocodile and a 

 giant tortoise. Another important locality is the Casimba 

 in the Sierra de Jatibonico, in central Cuba, a fissure spring 

 at the bottom of a ravine, where many bones have been 

 found. Although a full account of these remains was in 

 preparation by the late Dr. W. D. Matthew and Prof. Carlos 

 de la Torre, this seems to have been indefinitely postponed 

 through the death of the former. Nevertheless, in pre- 

 liminary papers (Torre and Matthew, 1915; Matthew, 1918, 

 1931) they distinguish no less that four genera, to which names 

 are given. Matthew (1918, p. 660) restricts Megalocnus to the 

 largest of these, "about the size of a black bear"; the smallest 

 is Microcnus, "about the size of a cat, and there are two of 

 intermediate size, Mesocnus, with a rather long, narrow muzzle, 

 and Miocnus, with a broad, square muzzle." To this last 

 genus Acratocnus of Puerto Rico and Hispaniola is said to be 

 related. Possibly, too, Parocnus may be found to be closely 

 related to one of the two intermediate genera or even identical 

 with it, when better material is assembled and restudied. The 

 three other genera, Megalocnus, Microcnus, and Mesocnus, 

 have large tusks of a "peculiar dished shape, with a tendency 

 to approach toward each other like the incisors of rodents. " 

 Matthew regards the Cuban ground sloths and the Puerto 

 Rican Acratocnus odontrigonus as descendants of a common 

 ancestral type of Upper Miocene or Lower Pliocene age, related 

 to that of Megalonyx. Matthew adds that "there is so much 

 individual and age variation in ground sloths that it is difficult 

 to say how many species of these genera are present. Mega- 

 locnus occurs abundantly both at Ciego Montero and the 

 Casimba, but apparently only one species at Ciego Montero, 

 while at the Casimba there may be two or three. The species 

 found at the eastern end of the island agree better with the 

 Casimba forms than with the Ciego Montero species. Of the 

 smaller forms there are clearly two species of Mesocnus, but I 



