498 MR. R. LYPEKKER ON SCELIDOTHERIUM. _ [Nov. 16, 
genus occupying in some respects an intermediate position between 
Megatherium and Mylodon, but also showing evidence of a still 
more widely extended affinity. The dentition is decidedly nearest 
to that of Mylodon, 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 family. The peculiar Mylodon 
darwini (generically separated by Reinhardt under the name of 
Grypotherium) is the form by which Scelidotherium 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, S. 
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 J/yrmecophagide, that it is quite 
easy to imagine how that family may have taken origin from some 
member of the Megatheriide ; 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 Bradypodide 
suggests that the modern arboreai Sloths may also originally have 
sprung from some early member of the same great family of Ground- 
Sloths. 
EXPLANATION OF THE PLATES. 
Puate XLVI. 
Scelidotherium leptocephalum, Owen. Frontal aspect of the cranium; from the 
Argentine Republic. British Museum, No. 37308. The occiput has been 
restored from another specimen. 4. Ja, lachrymal; za, nasal; mz, 
maxilla. 
Pruate XLYII. 
Scelidotherium bravardi, Lydekker. Frontal aspect of the imperfect cranium ; 
from the Argentine Republic. British Museum, No. 37626. 4. Letters as 
in Plate XLVI. 
Prater XLVILII. 
Scelidotherium chiliense, Lydekker. Frontal aspect of the cranium, British 
Museum, No. M. 2819. 4. Letters as in Plate XLVI. 
Puatze XLIX, © 
Fig. 1. Scelidotherium bravardi, Lydekker, The mandible associated with the 
cranium figured in Plate XLVII. British Museum, No. 37649. 3. 
2. Scelidotherium chiliense, Lydekker. The anterior part of the mandible; 
from Chili. British Museum. No. M. 2821. 3. 
3. Scelidotherium leptocephalum, Owen. The left astragalus; from Pata- 
gonia. Mus. Roy. Coll. Surgeons, No. 3520. 4. a, external trochlear 
ridge for tibia ; 4, internal tuberosity. 
4. (?) Scelidotherium bravardi, Lydekker. The left astragalus; from 
Brazil. British Museum, No. 186204, 43. Letters as in fig. 3. 
Fi iit 
