﻿MYRIACANTHIDiE. 47 



slightly concave inner face, and consisting of tubules 

 arranged at right angles to that face (PI. II. fig. 2 b). The 

 palatine tooth, so far as preserved, exhibits a gently tumid 

 oral surface, completely covered by the tritoral area, 

 which is again enveloped by a thin layer of hard dentine 

 inwardly. Egerton Coll. 



P. 4664. Type specimen of Prognathodus guentheri, described and 

 figured by Egerton, loc. cit. The fossil exhibits the 

 anterior aspect of the mandible and all the teeth, except 

 the right palatine, the mouth being opened and the upper 

 dentition displayed from the oral aspect. The mandibular 

 cartilage is flattened, so that both rami lie in one plane, 

 and there is no suture at the symphysis. Two small 

 labial cartilages rest upon its median portion, and at the 

 left extremity is a triangular dermal plate, ornamented 

 with tubercles and provided with two large marginal 

 processes, as shown in Egerton's figure. The dentition is 

 re-figured in the accompanying PI. II. fig. 1. The mandi- 

 bular teeth (" maxillary, "Egerton) are considerably broken 

 (mdi) and the oral face is evidently abraded, so that the 

 punctate tritoral areas appear as if confined to the promi- 

 nences. The presymphysial tooth (ps.) displays the outer 

 convex face, coarsely striated longitudinally ; and the 

 irregularity of its inferior extremity suggests that that 

 was its point of insertion. Only the anterior half of the 

 oral face of the left palatine tooth (" mandibular tooth 1," 

 Egerton) is exposed (pi.) ; but the whole of the attached 

 surface of this tooth has been extricated from the matrix 

 since its description by Egerton, and its precise outline 

 can thus be ascertained. It exactly agrees with the 

 corresponding tooth of the new specimen (No. P. 151) 

 described below ; but the only detail that can be 

 observed upon the oral aspect is the presence of a broad 

 depression extending obliquely backwards from the antero- 

 external angle, and this was perhaps not covered by the 

 tritoral area, which seems to extend over all other parts. 

 The abruptly deflected anterior margin of the palatine 

 tooth abuts against the small triangular vomerine tooth 

 (" mandibular tooth 2," Egerton), in advance of which is 

 the still smaller tooth (" mandibular tooth 3," Egerton), 

 either as a separate element or merely an accidental dis- 

 memberment. The principal vomerine tooth (v.) has a 

 gently tumid oral surface, with one large tritoral area and 



