156 WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 
(fig. la) is proved to be twice as broad as its maximum length at the 
outer end, but is preserved chiefly in impression ; the external 
face of the portion of the bone remaining is not ornamented 
by tuberculations. That of the left side (fig. 1, p.t.) is much 
fractured. Some of the characteristic cheek-plates are observable, 
but almost entirely as impressions of the inner face. The upper 
posterior suborbital {s. o. 1) is arched inwards above and is clearly 
deeper than its maximum width ; but it is uncertain to what extent 
it was overlapped by the upper posterior circumorbital (c. o. \], of 
which only a crushed fragment remains below. The lower posterior 
suborbital (s. o. 2) is a comparatively small plate, only about half as 
wide as the one above. The lower posterior circumorbital (c. o. 2) is 
completely shown, except at its anterior pointed extremity, and is 
twice as broad as deep. Merely a fragment of the maxilla {mx.) is 
preserved, with a few small slender teeth ; but the long and narrow 
supramaxilla (s. mx.) is well displayed, attenuated and pointed in 
front, of nearly uniform depth in its hinder two-thirds, and gently 
rounded behind. The mandible {rnd.) is too obscure for description, 
but exhibits traces of relatively large conical teeth. The preoper- 
culum {p. op.) is fragmentary, but displays the usual degree of 
expansion characteristic of the genus. The operculum {op.) is a 
little obscured above, but seems to have been almost as broad as 
deep. The breadth of the suboperculum {s. op.) is slightly more 
than twice the maximum depth of its exposed portion, and the well- 
preserved outer face of the bone is ornamented with an extremely 
delicate and closely arranged rugosity. Below the preoperculum are 
traces of the robust branchiostegal rays (hr.), but the remainder of 
the branchiostegal apparatus is destroyed. The triangular supra- 
temporal plate (s. t.) is partly exhibited in position, and four of the 
enlarged postclavicular scales (p. cl.) are displaced, but no other 
traces of the pectoral arcli are recognisable. The endoskeleton of 
the trunk is not shown, and the scales, though preserved, are much 
abraded. None of these exhibit any markings beyond the concentric 
lines of growth ; and the exposed area of those on the ventral aspect 
is distinctly equilateral, while that of the scales on the upper part of 
the flank is much deeper than broad. 
