524 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [June 25, 



to be the edentulous beak-like part of the prsemaxilla, known to us by 

 Mr. Fox's skull. That which I judge to be the trenchant border has 

 the same length as the edentulous part of the mandible. 



Teeth. — The other remnants of upper and lower jaw, though very 

 fragmentary, thrownew light on the dentition of Hypsilophodon, sothat, 

 with this and several teeth which had fallen out and were recovered 

 from the clay by washing, I can now illustrate nearly every phase 

 in the life of a tooth, from the immature crown, which had not come 

 into use, to the worn-out stump. 



The right mandible just described had at least ten mature teeth 

 in use, of which the crowns of four only remain ; and these exhibit 

 the characters of the maxillary teeth of Mr. Pox's skull. The last 

 tooth is smaller than those immediately before it. The 2nd-6th, 

 counted from behind forwards, were larger than the four next pre- 

 ceding them. The crowns of three of these are broken off and lost ; 

 but one remains. It is worn nearly to the root ; and a young unused 

 crown rising up at the inner side of this stump shows these teeth to 

 have corresponded in shape and size to the anterior smaller maxillary 

 teeth in Mr. Fox's skull. Between the foremost of these teeth and 

 the edentulous extremity of the jaw, the outer parapet of the den- 

 tary bone has been broken away : no teeth remain here ; but I fancy 

 I can discern traces of three alveoli suitable for the reception of the 

 roots of teeth of the cylindrical form, such as are present in the hinder 

 part of the prsemaxilla. In the clay, at a short distance, lies one such 

 tooth ; and near this is the impression of another. As in Mr. Fox's 

 skull, so here, there are two forms of tooth — one simple and cylin- 

 drical, the other ornate and strongly compressed. 



Cylindrical teeth (fig. 7). — A perfect, mature tooth of this sort mea- 

 sured *4 inch ; of this, nearly -15 belong to the crown, which is sepa- 

 rated from the root by a slight constriction or neck. The root is 

 slightly contracted towards each end, and dilated in the middle ; its 

 cross section is nearly circular, and its surface is smooth. Two, which 

 I slit longitudinally, had a very large pulp-cavity filled with spar. The 

 crown is slightly and unequally compressed, the inner contour of its 

 cross section being slightly more convex than the outer. Its apex 

 is acuminate, and is slightly inflected, which renders the outer 

 longitudinal outline convex, and makes the inner one sinuous, con- 

 cave near the point, and convex towards the root. The outer and 

 inner surfaces meet angularly, making a low wing, within which and 

 parallel with it, upon the inner surface, is a minute shallow longitu- 

 dinal groove. In very perfect unworn crowns, the marginal wing 

 bears a row of minute tubercles, just visible in a strong light to the 

 unaided eye. Both surfaces are highly polished and smooth ; upon 

 the outer a few very minute longitudinal striae are discernible. 

 Towards the neck the surfaces are beset with excessively minute 

 tubercles (not recognizable as such without a magnifier), the collective 

 effect of which to the unaided eye is an extremely fine wrinkling. 



Compressed sculptured Teeth (figs. 4, 5, 6). — Both the varieties de- 

 scribed by Prof. Huxley from Mr. Fox's skull are amply illustrated by 

 my specimens, the smaller variety occurring in the front of the maxil- 



