338 A NEW MYLODON. 
considerably more compressed instead of being nearly the width of the articular 
head. The distal condyles are of about the size of those in the South American 
species, but in end view the concavity at the knee for the reception of the patella 
and its ligaments, is much flatter and apparently a little broader. The femur 
presents the following measurements :— 
Antero-posterior diameter of proximal condyle, circa 125 mm. 
Lateral diameter of same 118 
Depression for ihgamentum teres, base, 38; height, 58 
Breadth of femur across middle of shaft 165 
Width of articular surface for patella (anterior face of knee) 107 
Greatest width across distal condyles (posterior view) 198 
Greatest width of outer posterior condyle 68 
Greatest vertical height of same 58 
Greatest width of inner posterior condyle 82 
Greatest vertical height of same 97 
Ventral width of isthmus between distal condyles 58 
The patellae are almost squarely truncate across the top, but at the outer 
upper corner are bordered by a thick ridge of bone that projects above the general 
dorsal outline. Ventrally the sides of the bone converge to a blunt point. 
In M. robustus there is a raised portion of bone visible along the entire dorsal 
edge of the articular facet, as seen in posterior view. This facet is of different 
shape in the two patellae of the specimen studied. In one it is slightly narrower 
and longer than in the other, 39 to 44, and 113 to 102 in comparative diameters. 
The remarkably short and broad tibia is nearly identical with that of the 
South American Mylodon. That of the left side measures in extreme length 
between uprights 255 mm.; in extreme breadth across the proximal facets, 171 
mm. The broad thick shaft contracts to a width of 100 mm. at the middle 
and expands distally to 131 mm. across the malleoli. Of the two articular 
facets at the proximal end, the external has a practically flat surface, separated 
by a depression from the slightly hollowed and larger internal facet. The long 
axes of both are nearly parallel and at about 45 degrees to an antero-posterior 
line. In M. robustus the smaller facet is of slightly more oval outline with its 
axis nearly at right angles to that of the larger. These peculiarities are no doubt 
subject to much individual variation. The outer facet is the upper surface of 
a projecting shelf whose lower portion forms an articulation for the proximal 
end of the fibula, of roughly elliptical outline, transversely placed. The inter- 
nal malleolus at the distal end of the tibia is slightly less expanded than in 
