MYRIACAXTHIDJE. 
47 
slightly concave inner face, and consisting of tubnles 
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. 
4664. Type specimen of Prognathoclus guentheri , described and 
figured by Egerton, loo. 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 
(md.) 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 (Xo. 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 3Egerton), 
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 
