338 MESSRS. HANCOCK AND ATTHEY 



anterior and posterior : the former is a wide, hollow, arched, 

 scoop-like cutting-margin, which in some specimens is obscurely 

 and minutely crenulated or denticulated, and is usually quite 

 sharp. This portion occupies the anterior third of the crown ; 

 the posterior two-thkds is shield-formed, somewhat convex, with 

 the point directed backwards and the sides evenly arched out- 

 wardly. This is the crushing or grinding- surface, and is tra- 

 versed by strong transverse undulated ridges imbricated forward, 

 and divided by wide deep grooves. In fully developed specimens 

 there are six such ridges ; but the number varies, some having 

 four, others five ; and in the small, second lateral, oblique indivi- 

 duals there are only three. The ridges bend upwards at the 

 sides, and usually arch a little forward at the centre, where they 

 are most strongly undulated, and sometimes deeply notched and 

 angulated, roughened and granulated. But they vary consider- 

 ably in these respects, some being almost smooth ; and in one 

 of our specimens all the ridges are comparatively even, though 

 here and there slight undulations are perceptible. From this 

 comparatively smooth state there is every degree of undulation 

 to the most rugged. In fact, the smoothness is very much owing 

 to wear ; and in such specimens this portion of the crown is 

 generally much reduced in thickness. The form of the grinding 

 division of the crown also varies considerably. We have said 

 that the sides arch outwards ; they are, however, not unfre- 

 quently quite straight, and when this is the case, and the ante- 

 rior ridge is free from undulations, the area assumes the form of 

 an equilateral triangle, with one of the angles directed back- 

 wards : in two or three specimens the area is even wider than 

 long, with the lateral angles more acute than usual. In such in- 

 dividuals the scoop-like cutting-margin occupies half the crown. 

 The root is a wide plate as broad as the tooth, and tapers 

 slightly backwards ; behind, it is rounded, convex above and 

 concave below, and projects backwards on a lower plane, the 

 crown being elevated above its upper surface. 



The second primary or lateral oblique teeth are very inequila- 

 teral, one side being concave, the other convex ; they have only 



