278 Mr. A. 8. Woodward on the Myriacanthide. 
suggests itself as worthy of consideration; but, since the 
type specimen was entirely misinterpreted by Egerton, and as 
a new specimen in the British Museum (no. P. 6095) is now 
available for study, it is necessary, in the first place, briefly 
to recapitulate the principal features of this singular group of 
teeth. 
As pointed out by Dr. von Zittel *, the mandible of the 
type species, Prognathodus Giuenthert, was mistaken by Eger- 
ton for the upper jaw, while the upper dentition was ascribed 
to the lower; and thus arises the necessity for a complete 
revision of the subject. ‘The mandibular cartilage precisely 
resembles that of modern Chimeroids in exhibiting no sym- 
physial suture; and there is likewise a pair of small inferior 
labials. The right and left lower dental plates (m in Eger- 
ton’s figure) are of the form ordinarily observed in Chime- 
roid fishes and meet in a narrow facet at the symphysis ; 
but in advance of these is a median, bilaterally-symmetrical, 
incisor-like element (p, Egerton), also without doubt to be 
assigned to the mandibular dentition, and hitherto unparalleled 
in the order or subclass to which the fish belongs. ‘The pala- 
tine plates (1, Egerton) are large, expanded, and thin, elon- 
gated antero-posteriorly, and irregularly triangular in shape ; 
the outer margin of each is somewhat thickened, while both 
the outer and anterior margins are sharply deflected; the 
inner and posterior margins are thin edges, and there is no 
appearance of the close apposition of the right and left plates 
in the median line. ‘The vomerine dental plates (2, Egerton) 
are, as usual, much smaller than the palatines and in direct 
contact both with the latter and with each other; they are 
triangular in form and comparatively thin, and owe their 
robust aspect to the sharp deflexion of the margins. Still 
more anteriorly, in the known specimens, is a pair of small 
quadrangular, transversely ridged teeth (3, Egerton), which 
may be either independent elements or merely the accidentally 
detached front processes of the vomerine dental plates. 
Thus interpreted, it is obvious that the dentition of Progna- 
thodus Guenthert repeats the two most peculiar features noted 
above in the new specimen of ‘‘7schyodus orthorhinus.” 
There is the same incisor-like median tooth, referable to the 
lower jaw; and the front portion of each vomerine dental 
plate is transversely ridged in the same manner. Moreover, 
“Prognathodus”’ possesses tuberculated dermal plates upon 
the head, resembling the exampie alluded to above in the 
second specimen of “IJschyodus orthorhinus ;” and a careful 
comparison of all recognizable characters appears to the 
* Op. cit. vol. iii. p. 115, 
