166 WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 
been for the most part removed and an impression of its inner face 
alone remaining. Further back the cranial roof is preserved on the 
left side, and where the outer face can be observed it is shown to be 
very finely granulated. The hinder region of the cranial roof is 
raised in the manner characteristic of the genus ; while the sutures 
between the frontal, postfrontal, and parietal elements can be dis- 
tinguished as shown and described in the next specimen below. The 
indent along the base of the triangular occipital eminence is also 
conspicuous on the left side. The form of the two large post- 
orbital cheek-plates is almost completely shown, but the actual bone 
is preserved only in patches. Where the outer surface remains it is 
ornamented with very fine, closely arranged and flattened rugae and 
tuberculations, which exhibit a tendency to radiation at the margins. 
The impression of the inner surface of these plates seems to bear the 
imprint of numerous vascular pores ; and the well-preserved sub- 
orbital already mentioned on the right side shows that these pores 
penetrate to the outer face of the bone. The upper posterior sub- 
orbital (s. 0. 1) is trapezoidal in shape, a little broader than deep, and 
sharply bent inwards above. The lower posterior suborbital (s. o. 2) 
is almost triangular in shape, the apex turned forwards and partly 
excavated. The remainder of the cheek is so much fractured that 
fragments of only four plates of the circumorbital series (c.o.) are 
observable behind the eye. These, as usual, are small and must have 
been much broader than deep. One shows an extremely fine super- 
ficial granulation. The ossified sclerotic (scl.) is also imperfectly 
preserved. The long, slender maxilla (mca.) is shown in fragments, 
very finely rugose externally, and bearing traces of small, stout, 
smooth teeth. The form and proportions of the left mandibular 
ramus are indicated, but the teeth and the outer surface of the bone 
are almost completely destroyed. The limits of the relatively large 
dentary (d.) and the small angular (ag.) are approximately indicated 
by the direction of the structural lines of growth. The gular plate 
is well preserved, of the form and proportions indicated in fig. 2a, 
but the bone itself is much flaked. It seems to have been orna- 
mented with radiating rugae as fine as those of the other external 
elements. The branchiostegal rays are represented only by the 
