108 
FOSSIL JAWS OF MACHOPODIDJJ, 
mere, but decided, bulging of the base. The hind lobe of m 4 is 
in the mean of ten examples narrower than the fore lobe in the 
ratio 11 : 12. 
The contour of the mandible forward of the hinder molars is 
nearly straight. The upward curve beneath the anterior molars, 
always faint, is occasionally reversed and a continuous curve 
produced from the inflected angle to the symphysis. 
Maxillary. — P. 4 (PI. xvn. fig. 8). In a tooth recently come into 
position the general form is an isosceles triangle with the inner 
side irregular and the angles rounded. Diameters 191 : 100. 
crest subcentral, parallel with the outer side of the base. Mesial 
two-fifths of the outer side of the crown deeply impressed, with 
three strong vertical folds rising to the crest. Ledge occupying 
mesial two-thirds of the inner side of the crown, with a raised 
basal rim commencing at the hinder end of the anterior cusp; 
within the rim the ledge is deeply concave and is traversed by 
four ribs ascending on the lobe to the crest. Intero-posterior cusp 
wide, joined to the side of the lobe; behind it to the outer side a 
deep transversely elongate pit, which is enclosed behind by the 
posterior surface of the lobe. 
By contraction of the intero-posterior cusp the form may become 
regularly oblong, the tooth being then scarcely broader behind 
and its diameter 178:75, or the like form may result from a 
dilatation of the fore end of the basal rim to an equality with the 
extent of the intero-posterior angle; the tooth in this case may 
present a gibbosity near the fore end of the inner side. The ribs 
of the outer side of the crown may be reduced to two in number. 
The basal rim of the inner side is generally broken up into from 
two to five tubercles, usually one at the base of each vertical rib. 
P. 8 (PI. xvii. fig. 7) in a fresh condition is irregularly sub- 
triangular, with the fore end rounded. Mesial diameter 133 : 77. 
Crest well to the outer side of the central line, parallel with the 
outer side of the base. Mesial half of the outer side of the crown 
impressed, with two strong vertical folds. Ledge as in p. 4 but 
gradually dilating as it nears the intero-posterior cusp, which is 
