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the zygoma, the supratemporal process rising obliquely ; pterygoid 
bones thin and compressed ; crotaphite impression approaching near 
to the occipital ridge; tympanic bone reduced and separate; (the 
foregoing characters can of course apply only to the Mylodon robustus, 
it being the only species of which the cranium is known ;) lower jaw 
broad and more or less prolonged in front, the lower outline straight, 
the condyle depressed ; teeth —, the anterior ones rounded or tri- 
gonal, the posterior ones larger, trigonal in the upper jaw, gradually 
becoming bilobed in the lower. The species can only be characterized 
by the lower jaw, as it is the only part that is known in all of them. 
The characters are taken chiefly from Prof. Owen’s works. 
M. Darwintt. 
Lower jaw much produced anteriorly, with a double mammelliform 
tuberosity upon the symphysis below. The first tooth rounded or 
subtrigonal, the second subelliptical, with a slight depression on the 
inner side; the third subquadrate, grooved on the inner side; the 
posterior internal angle produced ; the fourth bilobed, sharply grooved 
on the inner side. 
M. Harvant. 
Lower jaw with the symphysis short; the second tooth sub- 
quadrate, grooved on the inner side, with the posterior internal angle 
produced ; the third trapezoid, obliquely placed, with the inner side 
rounded ; the fourth bilobed, the inner groove biangular, and a small 
shallow one anterior to it. 
M. ropvustus. 
Lower jaw produced and very broad anteriorly, the first tooth 
round, the second subtrigonal, grooved internally, the third sub- 
quadrate, oblique, the fourth bilobed, with a deep scallop on the 
inner side and a smaller one anterior to it. 
GLossoTHERIUM, Owen. 
Crotaphite impression approaching near to the occipital ridge ; 
tympanic bone reduced and separate. The general cranial characters 
are unknown, but the fragment is recognizable by the great size of 
the surface for the stylohyal bone, and of the precondyloid foramen. 
ScELIDOTHERIUM, Owen. 
Malar bone with a well-developed zygomatic process; the cha- 
racter of its frontal process cannot be determined through mutilation 
of the specimen ; crotaphite impression approaching near to the occi- 
pital ridge ; tympanic bone reduced and separate ; lower jaw greatly 
curved below, its condyle depressed ; teeth —. transversely extended, 
the anterior ones fully as large as the others, the first in each jaw 
elongate trigonal, the others gradually becoming bilobed, the last 
upper one trigonal. 
S. leptocephalum. 
