of Amphicentrum granulosum. 275 



abruptly projecting labial mass, whose oral margin forms a 

 ridge separated by a shallow groove from an inner ridge. 

 Seen from below, this groove terminates sharply behind by 

 the approximation of the outer and inner ridges, but is closed 

 in front by the prsemaxilla. On the outer ridge the dental 

 tubercles are few ; on the inner, which is more prominent, 

 they are more numerous, — less so, however, than on the 

 mandible, which is the converse of the maxilla, in that the 

 ridges approximate in front, the tubercles ceasing before their 

 coalescence, while the groove is open posteriorly ; the outer 

 ridge is also the more prominent "*. 



Now, few things are more clearly shown in the specimens 

 before me than that the maxilla is, on the contrary, a thin 

 plate, whose oral margin is quite edentulous, like that of the prae- 

 maxilla. It forms a somewhat triangular or, rather, trapezoidal 

 plate (mx, PI. IX. figs. 1 & 2), whose upper margin slopes 

 gently downwards and forwards, the posterior more rapidly 

 downwards and backwards ; the anterior margin, very short 

 and a little bevelled off, is in contact with the prsemaxilla, 

 which slightly overlaps it; finally, the oral margin, the 

 longest, forms a simple and rather sharp edge, along which 

 not the slightest trace of teeth or of dental tubercles can be 

 seen. The external surface of the maxilla is beautifully 

 ornamented with wavy ridges and wrinkles, which, save quite 

 in front and near the upper margin, where they are more 

 irregularly disposed, assume a general direction perpendicular 

 to the oral edge of the bone, stopping short, however, just 

 before reaching it, so as to leave here a very narrow smooth 

 border. Both in form and in external sculpture this bone 

 bears a great resemblance to the maxilla of Eurynotus, ex- 

 cepting, of course, that the obtuse rounded teeth with which 

 the latter is garnished are here totally absent. 



It is therefore clear that the bone reckoned as " maxilla " 

 by Dr. Young, and of which the original specimen from 

 Mr. Ward's collection, represented in his figure "j", is now 

 before me, cannot be that bone ; and the question next arises 

 as to Avhat it is. 



The twenty-six specimens of detached bones bearing tooth- 

 tubercles, submitted to me by Mr. Ward, easily fall into two 

 distinct sets. In the one, which includes the type specimen 

 of the so-called maxilla (PI. IX. figs. 5 & 6), the surface 

 exhibiting granulations is more flat, the dental tubercles less 

 prominent, and, indeed, quite obsolete on one of the two mar- 

 ginal ridges ; while in the other (figs. 9 & 10), the dentigerous 



* Op. vit. p. 300. t Op. eit. pi. xx. fi<r. 2. 



