A NEW MYLODON. 333 
Of the remaining sternebra there are five preserved, four of which are appar- 
ently consecutive and at the posterior half of the series. These are more or less 
squarish in dorsal view, with a demifacet at each corner ventrally, the two larger 
at the anterior corners. As in M. robustus the articulation of each sternal rib 
except the first is by means of these demifacets, and two others borne by a 
median ventral keel on each sternebrum. In two of the pieces this keel is nearly 
as long as the sternebrum, in another it is much shorter. The fifth sternebrum 
has no demifacets at the posterior corners, and so was probably the last to articu- 
late with the ribs. The hinder part of its keel is lost. This piece differs further 
in its narrowness and greater proportional length. It articulated with yet an- 
other posterior piece, which seems to be lost. In M.robustus the last piece of 
the sternum is similar to the one here believed to be the penultimate segment. 
Following are the measurements of these five pieces :— 
Ist 2d 3d 4th last 
Median length of dorsal surface 52 56 59 56 63 
Greatest anterior width across demifacets GO) iy G3 Sr 0 
Least transverse width (near middle) 51 49 49 40 33 
Greatest posterior width 0) Gy i) 4 al 
Greatest length of ventral keel 36 386 5 5 44? 
Greatest depth (tip of keel to dorsal border of sternebrum) — 69 53 55 —’ 
In a mounted skeleton of M. robustus in the Museum, there are eight sterne- 
bra. 
But five of the sternal ribs are entire, and these seem to be of the same type 
as in M. robustus. Two of the smaller measure 157 and 146 mm. respectively 
in greatest length. Distally there are two oval facets, their tips meeting, which 
articulate with the facets on the keels of two consecutive sternebra. A short 
distance proximal to these is a single rounded facet with more or less indication 
of two faces for articulation with the demifacets at the dorsal corners of the 
sternebra. The largest sternal rib preserved is 282 mm. long, and differs in 
having a single large terminal facet instead of two. It has also an oval elevated 
rugosity 38 < 18 mm., at the first third of its length dorsally, which probably 
served for muscle attachment. In the middle portion of their length these sternal 
ribs show a T-shaped or Y-shaped cross section, the stem of which forms a ventral 
keel. Two other small sternal ribs are flattened and without the keel. In one 
of these the terminal facets for four articulations are continuous, forming a closed 
ring. The distal portions of those ribs that did not articulate with the sternum, 
ended in tapering bony points, one of which is preserved. 
