WOODWARD : FOSSIL FISHKS OF THE UPPER LIAS OF WHITBY. 167 
merest fragments ; but the displaced operculum is nearly complete 
and shown to be as broad as deep. 
A second specimen in the British Museum (No. P. 884b) exhibits 
the opercular and branchiostegal apparatus and a great part of the 
cranial roof. The outer cranial bones are not so much flaked as in 
the last specimen, and the fine granular ornament is beautifully 
displayed. The total length of the skull must have been twice as 
great as its maximum width, and the snout, though imperfect, is 
shown to have been remarkably acute. There is no trace of a median 
frontal suture, while it is not clear where the frontals end and the 
dermal ethmoidal armature begins. The long and narrow post-frontal, 
however, is distinct on the left side, extending from above the middle 
of the orbit to the front border of the posterior suborbitals. The 
wavy and well-defined hinder border of the frontal element is con- 
spicuous on the left side, not so far back as that of the post-frontal, 
directly transverse on the lateral part of the skull, directed some- 
what forwards as it is traced up the side of the median triangular 
eminence. The whole of this border is in contact with the parietal, 
which is of longest extent in its flattened outer lateral portion and 
becomes narrowed as it rises to meet its fellow of tlie opposite side in 
the median eminence. This line of meeting is unfortunately broken 
and displaced. The squamosal seems to have been removed and 
destroyed. The fragmentary remains of the cheek do not add any- 
thing to the information obtained from the previous specimen, except 
that the large supramaxillary plate is indicated at the back of the 
maxilla on each side. This element, however, is better shown in the 
next specimen. The opercular apparatus is more worthy of descrip- 
tion, and that of the left side is shown of the natural size in pi. xxi., 
fig. 4. The operculum (np.) is triangular in shape, and seems to be 
about as deep as broad, the preoperculum being obviously displaced 
somewhat backwards and covering its anterior border. The sub- 
operculum (s. op.) is irregularly rhombic in shape and much broader 
than deep, but the preoperculum also covers an undetermined extent 
of its anterior border. Both these bones are much abraded, but 
show distinct traces of the characteristic external ornamentation. 
The preoperculum {p. op.) is semi-lunar in form, much extended, and 
