1896.] MAMMALIAJf DENTITION. 573 



very late eJongation of the jaw, not to the retention of a primitive 

 character. 



The Molar Teeth. 



In the younger of my two specimens m. 1 alone was developed, 

 while in the older stage two molars were present above and below ; 

 iu the latter specimen a very strong lingual development of the 



dental lamina was noticeable in relation to —^. that connected 



m. 1' 



with ra^ being specially large (Plate XXV. fig. 26, d. I.), and a less 

 marked but similarly related structure was observable iu connec- 

 tion with ra. 2. 



, The Cusps. 

 The posterior premolars and all the molar teeth belonging to 

 the upper jaw of this genus exhibit a high triangular crown 

 surrounded by a low cingulum, this latter being most marked in the 

 postero-iiiternal region of the toolh (Plate XXVI. flg. 34) ; the 

 trigon is characterized by the presence of 3 cusps, of which the 

 antero-interual (s) is the dominaut and is connected by an oblique 

 ridge with the cusps usually regarded as the paracone and metacone 

 respectively (2, 3) — this tooth apparently presenting an almost pure 

 tritubercular type'. On examining i£j^ in my oldest specimen, 

 this tooth was found to be composed of a prominent main cone 

 slightly inclined inwards, undoubtedly the protocone of the 

 adult tooth ; while growing out low down from the external surface 

 of this main dental germ were two smaller cones — a slightly more 

 pronounced anterior one occupying the position of the future 

 paracone, and a less developed postero-extenial cone situated well 

 behind the main cone, i. e. the exact position of the metacone. 

 The order of cusp-development is given below : — 



1. Protocone. 



2. Paracone. 1 ivr 1 • li. 



3. Metacone. | ^^'''^^ simultaneous. 



In the deciduous 4th premolar likewise the protocone develops 

 first, but here the metacone is in advance of the paracone. 



The lower molars and posterior premolar are beautiful examples 

 of the trituberculo-sectorial tooth, consisting of a high trigon and 

 a low slightly developed heel ; the three cusps of the trigon are 

 pronounced — the protoconid (antero-external) being the largest, 

 the metaconid is next in size and almost hidden by the former as 

 it lies immediately internal to it, the paraconid being the smallest 

 and most anterior cusp. 



The development of these cones is well seen in m. 1 &m. 2 of my 

 older specimen, and it is at once obvious that the protoconid is the 

 origiual dentine germ, the other cusps being later outgrowths from 



' The upper cheek-teeth of Hemiccntetes should be examined by tvituber- 

 culists, for in this genus a complete transition between the tricouodont 

 premolars and the trituberculate molars can bo seen. 



