﻿1S60.] 



HUXLEY MACKAITCHENIA BOLTVIENSIS. 



81 



the surface appears, however, to have been more evenly flat. The 

 inner perpendicular face of the impression presents two concavities, 

 separated by a slight ridge. 



More of this tooth is preserved than of any other ; the outer wall 

 of the maxilla is, for the most part,' preserved over it, and encloses the 

 alveoli of two external fangs. There is evidently at least one, and 

 perhaps two, internal fangs. The whole thickness of the inner and 

 posterior part of the crown is preserved, and the posterior and inner 

 half of its worn face ; the rest of the tooth is broken away. The 

 posterior and outer fang, partially exposed, is 0*3 of an inch long, 

 conical, and slightly inclined backwards, as well as upwards and 

 inwards. The crown, where it joins the fang, is 0*4 of an inch long ; 

 so that it must have widened a little below. The vertical height of 

 the crown of the tooth posteriorly and internally is hardly more than 

 0-15 ; anteriorly and internally it is broken ; but, when entire, it had 

 a height of at least 0-2. The inner surface of the tooth is divided into 

 two tolerably well-marked subcyHndrical faces, which correspond with 

 the impressions on the inner wall of the coronal impressions. 



The outer moiety of the crown is altogether broken away ; the inner 

 moiety, broken anteriorly, exhibits in its posterior half a smoothly worn 

 facet, concave from before backwards, and inclined not only down- 

 wards but slightly backwards. A narrow fringe of enamel appears to 

 surround the worn dentine of this face, which is wider in the middle 

 than at the two ends. The true outer face of the enamel can be 

 traced from the inner face of the tooth, continuously, round the pos- 

 terior boundary of this worn facet, and as far as its most dilated 

 portion on the inner side. It is concave outwards, and presents a 

 slight inflexion midway between the posterior end of the facet and 

 its middle dilatation. Beyond the dilated middle of the facet, its 

 enamel- wall seems to have been united with that of the opposite 

 half of the tooth ; but it is traceable forwards, becoming concave 

 externally, past the anterior end of the worn facet, to the anterior 

 margin of the tooth, where it bends round and again becomes con- 

 tinuous with the enamel of the inner face. 



This tooth, therefore, appears to have possessed an internal divi- 

 sion, elongated from before backwards, surrounded by a narrow band 

 of enamel, — having its inner contour produced into two convexities, 

 separated by a slight vertical depression, while its outer wall pre- 

 sents two concavities, separated by a slight ridge which lies rather 

 behind the level of the depression on the inner face. By use, the 

 posterior part of this division wore down into a facet, concave from 

 before backwards, and separated, by a transverse ridge, from the facet 

 in front of it. A longitudinal fossa separated the posterior moiety, at 

 least, of this division of the tooth from the outer division. 



Imperfect as is this fragmentary grinder, certain important con- 

 clusions may, I conceive, be very safely drawn from its structure. 

 The predominance of the longitudinal, to the exclusion of transverse 

 valleys and ridges in the crown of the tooth, the distinct, though 

 not strongly marked, crescentic form of the internal division of the 

 tooth, and its short crown, remove it from the teeth of any known 



vol. xvri. — part i. e 



