TETEACONODON OR CIKEEOTHERIUM. 151 



The external outline of the crown viewed in profile gives a 

 sweep of salient and re-entering angles getting more and 

 more obsolete forwards, from advanced detrition, with a 

 small prominence in the open angles or swell in the col- 

 liculi, marking the commencement of the transverse ridges. 



The vertical outline externally of the outer coUiculi, from 

 the root to the apex, is but slightly convex. 



Besides the complication of the spur in the last tooth 

 there are other diEFerences between the two, dependent on 

 form and detrition. 



To begin with the last, which is the more perfect and least 

 worn : — 



This tooth, exclusive of the spur, is a little longer than 

 broad ; and the distinction of the crown into two pairs of 

 processes, and of each pair into separate coUiculi, is well 

 marked. 



The two outer processes have the same form, differing only 

 from wearing, the posterior being more pointed, and their 

 outer surface rises to the apex with little of a curve ; they are 

 flattened laterally, sloping right and left. Their inner surface 

 inclines from the point, downwards, at a considerable angle ; 

 the anterior one is worn down to a disc, which is oblong 

 transversely, and surrounded by a complete belt of enamel ; 

 in the posterior one, the enamel is scarcely touched, the 

 surface is marked with slight inequalities, the disc is very 

 small, and the posterior edge of the process is notched into a 

 few tubercles. Around the base, at their connected aspect, 

 both processes are bounded by a fissure, which separates them 

 from the rest of the crown. 



In the angle between these coUiculi lies the middle trans- 

 verse crest or ridge of enamel. It is notched, narrow, and 

 little prominent. It arises by a slender pUlar in the external 

 fossa, where the shaft is contracted, runs forward a short way, 

 and is then lost in detrition. The posterior crest arises in a 

 considerable lobule or swelling of the hind process at its base. 

 It is well notched, and runs forward in a sweep between the 

 process and the spur, terminating at the outer third of the 

 latter. The anterior ridge arises also in a swelling of the 

 corresponding process. It is partly worn and has a flattish 

 surface. It stretches across (with an accidental breach of 

 continuity in the fossil) along the margin of the crown, and 

 descends in a curve, so as to turn roimd a little way on the 

 shaft. 



Now, in description of the inner divisions : — The protube- 

 rance of the coUiculi has disappeared ; they are trimcated 

 from wearing down to a flat disc. The corresponding por- 

 tions of the shaft, from which the processes rise, are more 



