An Almost Perfect Skull of a New Primitive Theriodont. 201 



Dentition. 



On the ]'ight side the teeth are fah'ly well preserved, but badly on 

 the left. The teeth are more UTegular than is usual in Theriodonts, 

 and it is difficult to be quite certain of their determination. 



Beginning in front, we find exposed on the right side of the skull 

 the point of a rather small but probably fully formed tooth (fig. 6, i'). 

 This is doubtless one of a pair which may be regarded as the first 

 incisors. This tooth is follow^ed by a larger pointed tooth, which is 

 seen on both sides of the skull, and which may be regarded as the 

 2nd incisor. On the right side, between this 2nd incisor and the 

 next developed tooth, is a diastema of sufficient size to have accom- 

 modated a third tooth as large as or slightly larger than the 2nd. 

 This tooth, however, has disappeared, and the point of apparently a 

 young tooth is seen coming down to fill the gap. On the left side 

 we find the remains of the root of the old 3rd incisor, while behind 

 it and slightly internal to it is the root of the succeeding 8rd incisor^ 

 The 4th incisor is to be seen on both sides, as a well-developed 

 pointed tooth, slightly larger than the 2nd incisor. Behind the 4th 

 is present on both sides a 5th incisor. This 5th is somewhat 

 smaller than the 4th, though possibly this may be due to its being 

 " a younger tooth which has replaced a lost older 5th incisor* 

 Though on the outer surface of the skull the suture between the 

 maxillary and the premaxillary is in a line with the anterior border 

 of the 4th incisor, the root of the 4th incisor is undoubtedly, and 

 that of the 5th almost certainly, fixed in the premaxillary bone. 



So far, then, as the premaxillary teeth are concerned we may safely 

 assume that there are 5 incisors, and also that there is a dental 

 succession. But whether a definite deciduous dentition is replaced 

 by a single permanent set, or whether each tooth when lost is 

 replaced by another indefinitely it is impossible to decide with 

 certainty. 



Those incisors which are w^ell displayed show the posterior borders 

 finely serrated. 



Immediately behind the last incisor in most of the Theriodonts 

 hitherto discovered there is present a large canine, but in this skull 

 the 5th incisor is followed by tw^o large teeth, either of which, if 

 alone, would unhesitatingly be regarded as the canine. The first of 

 the two is not very much thicker than one of the incisors, but is 

 about twice as long. It is only very slightly curved, and is 

 remarkable for being, unlike the other teeth, serrated both in front 

 and behind. The second of the large pair is situated a little behind 

 the first, and slightly external to it. It is a powerful tooth — about 



