108 FOSSIL JAWS OF M ACllOPODID.K, 



mere, but decided, bulging of the base. The hind lobe of m* is 

 in the mean of ten examples narrower than the fore lobe in the 

 ratio 11: 12. 



The contour of the mandil)le 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 f'^om the inflected angle to the symphysis. 



Maxillary. — P.^ (PL xvii. 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 tlie crown deeply impressed, w^ith 

 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 ma}^ 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 crow^n may be reduced to two in number. 

 The basal rim of the inner side is generally Ijroken up into from 

 two to five tubercles, usually one at the base of each vertical rib. 



P."^ (PL 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.* but 

 gradually dilating as it nears the intero-posterior cusp, Avhich is 



