AVOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 329 
and rather coarse tubercular ornament ; but the relative proportions 
of these elements seem to be approximately similar to those of the 
specimen already described. The margin of the orbit (orb.) is clear 
on the right side, being defined as usual by a complete ring of 
circumorbital plates {c. o.). The uppermost circumorbitals, which 
are in contact with the frontal margin, seem to be the largest, 
and two are especially well preserved on the left side, where 
the tuberculated extei'nal surface is shown. The foremost of 
these upper plates is trapezoidal in shape, not only forming the 
antero-superior part of the circumorbital ring, but also extend- 
ing forwards above the hinder of the three antorbital plates 
(a. o.). Each of the latter is deeper than broad, with a com- 
paratively smooth external surface ; and the three plates together 
completely fill the space on the cheek between the cranial roof, the 
upper jaw, and the circumorbital ring. Of the comparatively 
large hinder cheek-plates or suborbitals, only the two lower 
elements remain on the right side (.s. o.) These are irregularly 
trapezoidal in shape, as indicated in the figure, and their external 
surface seems to be rugose rather than tuberculated. The removal 
of the upper suborbitals lias exposed the greater part of the 
hyomandibular (hm.) ; but both this and the jaw are too imperfectly 
displayed for precise description. Remains of a delicate lamina 
of bone, with traces of a close series of relatively small and slender 
styliform teeth on its oral border, may doubtless be interpreted as 
representing the maxilla {nix.), and this bone is clearly deeper 
behind than in front. The premaxillse are lost, and the maxilla is 
also destroyed on the left side, where is exposed a thick, tooth- 
bearing bone, evidently to be regarded as the vomer (fig. All 
the teeth borne by this element are broken except two, and these 
are both stouter and larger than those of the maxilla ; they have 
a tumid crown on a styliform base. The mandible is very much 
broken and exhibits no special features of interest. Adjoining the 
posterior border of the two lower suborbital plates, the inferior 
slightly expanded and rugose end of the preoperculum {p. op.) is 
well shown, and fractured remains of this element are traceable 
upwards as far as the hinder angle of the squamosal. Although, 
