Mr. T. Attliey on Autliracosaurus Russelli. 163 



for two thirds of the length of the light-coloured spindles ; it is 

 tlierefore longer, is more distinct, and very sinuous. 



The dentinal tubes radiate as before from the whole margin 

 of the pulp-cavity into both the light and dark dentine ; those 

 passing into the former, after the most beautiful wavy Avind- 

 ings, end in the sides of the infolded peripheral band ; those of 

 the latter radiate to the periphery. No granular layer of den- 

 tine is seen in this section. 



Fig. 4 is a transverse section a little below the alveolar 

 border, a portion of which is attached to the section. The 

 tooth has at this part been crushed, and parts of the dentine 

 are here and there displaced ; Irat it can be seen that the full 

 complexity of the tooth is here displayed, and that the cavity 

 is elliptical. The dark dentine of the exterior of the tooth is 

 much less in proportional size than the light. The spindle- 

 shapes of the latter are no longer visible, but are represented 

 by tracts passing in from the dark exterior and folding upon 

 themselves as they pass towards the pulp-cavity, the outline 

 of which is far from distinct, owing to the breakage of the 

 parts around. Into each of these tracts enters, from without, 

 the narrow peripheral band noticed under fig. 3 as being very 

 light-coloured and sinuous. In fig. 4 this narrow band is much 

 more sinuous, and follows the windings or convolutions of the 

 light dentinal tracts to near their extremities, which are fre- 

 quently continuous with each other ; but the infolded narrow 

 tracts are not so, keeping separate. The narrow bands are 

 here dark instead of light in colour, and granular. The folded 

 tracts are here and there separated from each other by clear but 

 irregularly shaped spaces, which are parts of the offsets of the 

 pulp-cavity. 



There are, intervening between the commencements of these 

 long winding tracts at the peripheral layer of dentine, others 

 which are very short, rudimentary, and mammillary, projecting 

 into the outer ends of the divisions of the pulp-cavity. These 

 also have a narrow dark band of granular dentine in their in- 

 terior. The same arrangement occurs in the teeth of Loxomma. 



The dentinal tubes all radiate from the margins of the central 

 pulp-cavity and its ramifications ; most of them pass through 

 the light-coloured dentine of the sinuous tracts, and end in the 

 narrow dark band running through them ; those, however, 

 which radiate outwards from the ends of the offsets of the 

 pulp-cavity are spread out in a fan-like expansion, and, after 

 passing through a series of finely arched lines crossing them, 

 reach the exterior of the tooth. 



The teeth of Anthracosaurus are, in fact, like those of 

 Loxommoj formed of a series of toothlets surrounding the pulp- 



