564 MB, M. F. wooDWABD ON [May 5, 



attained equal importance with the trigou and developed two 

 large cusps, an internal entoconid and an external hypoconid. 

 This tooth is further specialized in the partial suppression of the 

 paraconid, the antero-interual cone of the trigon, while the pro- 

 toconid (antero-external) and the inetaconid (postero-internal) are 

 very large. 



Taking the case of the upper molar first, in both my specimens 

 m. 1 was fairly advanced, sliowiug indications of four cones, viz., 

 the para-, meta-, proto-, and hypo-cones, here mentioned in order 

 of size ; the hypo-cone was obviously the last of the four to develop, 

 as it is only just recognizable in the younger specimen ; in the 

 older stage these cones are larger, and the iirst trace of the meta- 

 conule is here apparent. Thus in '"• 1 we can say for certain that 

 the metaconule appears last and the hypocone next to last, but 

 the trigon was too advanced in my S|)eciniens to determine the 

 developmental order of its cones. But where ■"■ 1 fails us m-3 

 comes to our rescue : in the younger stage two cones only were 

 apparent, viz., the two external ones, the para- and metacones, 

 and of these the former was much the largest and must obviously 

 have developed first ; immediately internal to this was a low shelf, 

 in the position of the iuture j^rotoeone, but at present no cone was 

 recognizable. In the older stage of this tooth the protocone has 

 appeared in this position, and a faint indication of the heel is 

 visible. We may thus state with certainty that the order of cusp 

 ontogeny is as follows : — 



1. Paracone l 



2. Metacone > Trigon. 



3. Protocone J 



4. Hypocone. 



5. Metaconule. 



In the lower jaw, as in the upper, the first molar was too far 

 advanced, all five cones being recognizable, but nevertheless 

 differing greatly in their relative sizes ; tlie following is their ordoi- 

 according to size, viz., proto-, meta-, ento-, hypo-, and paraconid, 

 the last being only just recognizable. An examination of m. 2 

 throws more light on the subject, for here only three cones are 

 developed as yet, viz., the proto-, meta-, and entoconid, a slight 

 antero-internal extension of the tooth-germ indicating the position 

 of the future paraconid, while a similar but larger postero-external 

 platform marks the hypoconid. The protoconid is larger than the 

 metaconid at this stage, and the metaeonid than the entoconid, 

 the probable order of development being : — 



1. Protoconid. 



2. Metaconid. 



3. Entoconid. 



4. Hypoconid. 



5. Paraconid. 



The ordinal position of the paraconid in the ontogeny may 



