PURBECK FORMATIONS. 73 



is higher, and it is followed by a minute basal ' talon,' probably the termination of an 

 internal ' cingulum.' 



This tooth is followed by jo 4 or d 4, approaching the Triconodont or true molar type ; 

 but with the basal cusps, especially the front ones, better developed than in any of the 

 succeeding true molars. The mid cone is also relatively higher in proportion to the first 

 and third cones ; but the whole crown is lower in proportion to its fore-and-aft extent 

 than in the succeeding molars. The apex of the mid cone reaches only to half the height 

 of the main cone of the antecedent premolars. The crown is entire ; no main cone is 

 worn or broken away. If it be the homologue of jy 4 in Triconodo7i it shows widely 

 difierent proportions and form. The superiority .of the middle to the fore and hind cnsps 

 favours its reference to the premolar series ; unless, indeed, it may belong to the deci- 

 duous series ; the symbol of d 4, in fig. 8a, is to be taken suggestively in reference to the 

 alternative above proposed. I have not felt justified to hazard this unique and brittle 

 evidence by burrowing after a possible hidden germ of a successional tooth. Behind 

 }j 4 or (/ 4 is a tooth (y« i) of the more usual Triconodont or Triacanthodont type, the 

 anterior and posterior cones, especially the latter, rising more nearly to equality vyith the 

 mid cone : there is neither fore nor hind talon. The crown of this tooth stands at a higher 

 level than that of the preceding, but rises not quite to a level with the apex of yj 3. 



The next tooth {m, 2), of the same type as in 1, slightly exceeds it in size ; it is equally 

 devoid of trace of ' cingulum' on the outer side here exposed. A minute tubercular pro- 

 minence at the fore part of the base may be the anterior end of an inner ' cingulum :' 

 thei'e is no trace of hinder talon. The next two molars (in 3, tn 4) are indicated by 

 impressions of their crowns in the present slab, that of the hindmost {m 4) being wholly 

 within the impression of the coronoid process. It is preserved in the opposite slab, with 

 that process (fig. 7 a, m 4). The penultimate molar, with the supporting part of the jaw, 

 as before stated, has been lost. 



Before quitting the survey of the slab (fig. 8), I may note that the outer wall of the 

 socket of the canine is prominent, and that in the depression between it and the less pro- 

 minent alveolus of the succeeding premolar the foremost and largest of three outlets of the 

 dental canal opens. These three foramina are in the same longitudinal line, midway between 

 the upper and lower borders of the ramus, pretty closely following each other. The outer 

 surface of the bone is finely punctate and longitudinally striate. The outer alveolar 

 border is serrate through the low angular processes rising into the intervals of the teeth 

 and their fangs ; the wall sinks at once from the alveolar outlets a short way, then slightly 

 swells outward before inbending to the thick lower border of the ramus, making the lower 

 half convex vertically. The symphysial contour forms, as in Triconodon mordax, an open 

 angle with the lower border of the ramus ; but this is continued in an uninterrupted 

 gentle curve to the condyle {b). 



In the opposite slab (fig. 7) the crown of the last molar {m 4) is exposed, incom- 

 pletely developed, in a formative alveolus at the fore part of the base of the coronoid pro- 



10 



