2o2 JOURNAL, BOMBAY NATURAL HIST. SOCIETY, Vol. XXV. 



behind this central portion. Viewed in profile from the inner side 

 (u' and b') cusps 4 and 5 are seen to be distinctly lower than in 

 the first stage ; the height of cusp 4 is now hardly equal to (in 

 stage I rather more than) the distance between the tips of cusps 4 

 and 5 ; the height of cusp o is still equal to or a little more than 

 (in stage I eonspicuoiisly more than) the same distance. 



Twelve individuals in this stage have been examined. Figs. 

 Ila, a' and lib, b' represent the minimum and maximum of wear. 



Third stcKje (fig. III). — The worn surfaces of the commissures 

 are considerably increased in area ; the breadth of cusp 5 is now 

 between 1/2 and 2/3 of the total length of commissure 2-5. 

 Equally, if not more, characteristic is the shape and enlargement 

 ofthe\vorn surface of cusp 6 ; the '-'triangle" occupies now not 

 merely the central portion of the ridge, but extends forward to the 

 very Ijase of cusp 4. Cusps 4 and 5 are worn considerably lower 

 (Ilia' and Illb'); the height of cusp 4 is much less than (about 

 1/2-2/3) the distance between the tips of cusp 4 and 5, the height 

 of cusp 5 is somewhat less than the same distance. 



There are seven individuals in this stage in the material from 

 October and November. The minimum and maximum of wear are 

 shown in fig. Ill a, a' and b, b'. 



Foiirth stage (fig. IV).— Easily distinguished from the third stage 

 by the increased breadth of the worn surfaces of the commissures, 

 the much enlarged triangular surface of cusp 6, and the consider- 

 ably lower cusps 4 and 5. The breadth of the worn surface of the 

 commissures at cusp 5 is now 3/4, or more than 3/4, of the total 

 length of commissure 2-5. The triangular surface of cusp G 

 tapered in stage III to a point at the foot of cusp 4, now it is quite 

 bi-oad in front, and the tooth worn quite thin at its antero-interior 

 corner. Cusp 4 is now so low that it only rises a little above the 

 worn surface of cusp 6, its height being about 1/3-1/4 the distance 

 between the tips of cusps 4 and 5 ; cusp 5 is correspondingly lower 

 its height about 1/2, or less than 1/2, of the same distance. 



Six individuals show this stage. Fig. IV represents as usual the 

 maximiim and minimum of wear. 



Fifth stage (fig. V).— The final stage, at least so far as my mate- 

 rial goes ; the molars are now worn down to the level of the gums. 

 The characteristic features of this stage are these :— Cusp 4 has 

 disappeared, having been worn completely down to the surface 

 level ; the worn surfaces of commissures 1-4 and 2-4 are therefore 

 now perfectly confluent with the " triangle " representing the 

 worn surface "of cusp 6. Cusp 5, which from the very beginning 

 is higher than cusp 4, has either nearly or quite disappeared. 

 Although these differences iu the degree of wear of cusp 5 are only 

 individual (not indicative of different " stages ", as the word is here 

 understood) it is important to note them, as they happen to give a 



