BY C. \V. 1)E VIS. 107 



Form. 



}faiidlhidar. — P.^ (PI. xvii. fig. (}) as it appears in a worn con- 

 dition is elongate with mesial diameters 178: 56, oblong tectiform, 

 ol)tusely pointed in front and not dilated posteriorly. Crest 

 central, nearl}^ level, obtusely serrated. The mesial two-thirds of 

 the crown compressed, l)ut more deepl}^ on the outer side, the 

 surface of which has corrugations with much fainter ribs in the 

 intervals; the inner surface similarly corrugated. Anterior cusp 

 distinctly defined by the mesial compression, its point low and 

 obtuse. Over the intero-posterior angle the crown is more tumid 

 than over the outer angle. 



The tooth varies much in proportions and other respects. The 

 diameters may V)ecome 161: 72 and the intero-posterior part of the 

 crown so tumid as to cause the inner surface of the crown to be 

 concave longitudinally, the tooth being then distinctly broader at 

 its hinder end. The number, strength and disposition of the 

 corrugations are all subject to varia.tion, and frequently under 

 stress of wear disappear altogether. 



P.'^ (PL XVII. tig. 5) in its maiden state is irregularly oblong, 

 with mesial diameters 103 : 51; its basal contour is arched on the 

 outer side, nearly straight on the inner, its fore end obtusely 

 pointed. Crest with tive low obtuse cusps, subcentral, curving on 

 to the intero-posterior angle, which is sufficiently tumid to render 

 the crown vertically concave on that side. Crown compressed, 

 with three ribs on the outer and two on tbe inner side, the outer 

 ribs graduated in length posteriorly. Anterior cusp moderately 

 distinct. 



This tooth also \'aries in shape, jDroportions and corrugation. 

 The intero-posterior angle may dilate sufficiently to render the 

 general form subtriangular, the mesial diameters may vary to 106 : 

 66, 89 : 86, the ribs maybe fewer in number or become indetinite. 

 Under wear the ribs quickly vanish. 



Molars.— {V\. xvii. tig. 9). The longitudinal linking ridges are 

 weak, the lobes but lightly convex posteriorly. Posterior 

 basal talons are generally present as erect plates, raised rims or a 



