498 MR. R. LYDEKKER ON SCELIDOTHERIUM . [NoV. 16, 



genus occupying in some respects an intermediate position between 

 Megatherium and MyloJon, but also showing evidence of a still 

 more widely extended affinity. The dentition is decidedly nearest 

 to that of Mylodo7i, while the hind foot approximates to that of 

 Megatherium, The crania of species like S. chiliense and S. 

 bravardi are those least removed from the Megatherium type, and 

 it is these species which come nearest to that genus in the structure 

 of the astragalus. All those forms in which the pes is known 

 exhibit the anchylosis of the first and second phalangeals of the third 

 digit, and the large claw of the same, which are such characteristic 

 features of the type genus of the ftimily. The peculiar Mylodon 

 darwini (generically separated by Reinhardt luider the name of 

 Grypotherium') is the form by which Scelidotheriuin is connected by 

 cranial characters with Mylodon ; and the connection is so close that 

 it becomes somewhat difficult to give a clear differential diagnosis. 

 In its extremely elongated facial region and peculiar astragalus, >Si. 

 leptocephalum is the species departing most widely from the Mega- 

 therium type, and it is probable, from the structure of the last-named 

 bone, that in this animal the pes was not everted as it is in Mega- 

 therium. In both its peculiar features S. leptocephalum makes such 

 a very marked approach to the Myrmecophagidce, that it is quite 

 easy to imagine how that family may have taken origin from some 

 member of the Megutheriidce ; while the remarkable resemblance in 

 dental characters existing between those members of the genus 

 Mylodon which have been separated by some writers under the 

 names of Pseudolestodon and Lestodon and the JBradypodidce 

 suggests that the modern arboreal Sloths may also originally have 

 sprung from some early member of the same great iamily of Ground- 

 Sloths. 



EXPLANATION OF THE PLATES. 



Plate XLVL 



Scelidotherivm Iqjfocephahcm, Of^en. Frontal aspect of the cranium ; from the 



Argentine Eepublic. British Museum, No. 37308. The occiput has been 



restored from another specimen. ^. la, lachrymal ; na, nasal ; nia; 



maxilla. 



Plate XLYII. 

 Scelidothernim. hravardi, Lydckker. Froutal aspect of the imperfect cranium ; 



from the Argentine Eepublic. British Museum, No. 37626. i. Letters as 



in Plate XLVI. 



Plate XLYIII. 

 Scclidofhcmim chiliense, Lydckker. Frontal aspect of the cranium, British 



Museum, No. M. 2819. ^. Letters as in Plate XLYI. 



Plate XLIX. 

 Fig. 1. Scdidofhcrium bravardi, Lydekker. The mandible associated with the 

 cranium figured in Plate XLVII. British Museum, No. 37649. ^. 



2. SceKdoiherium chiliciise, Lydekker. The anterior part of the mandible; 



from Chili. British Museum, No. M. 2821. J. 



3. Scelidofheriimi Icptoccphalian, Owen. The left astragalus ; from Pata- 



gonia. Mus. Eoy. Coll. Surgeons, No. 3520. ^. a, external trochlear 

 ridge for tibia ; b, internal tuberosity. 



4. (?) Scelidotherium bravardi, Lydekker. The left astragalus ; from 



Brazil. British Museum, No. 18620 A-. ;^. Letters as in fig. 3. 



