160 WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 
Oil the left side shows that it was Larger thau the parietal element; 
the froiitals are very large and exhibit traces of a fine ornamentation 
resembling that of the parietals. The sclerotic {scl.) is ossified, and 
there are fragments of finely tiiberculated cheek-plates. Traces of the 
hyomandibnlar {hm.) on both sides are too imperfect for description. 
The maxilla {mx.) is also a mere fragment, but it bears some small 
slender teeth. The anterior teeth (fig. la) are similarly slender but 
larger, and extend in a continuous spaced series round tlie obtuse 
end of the fossil which represents the rostrum. These teeth are ronud 
in section and smooth, only exhibiting a few vertical folds at the base; 
and they may belong either to the premaxilla or to an inner element. 
The mandible tapers to the symphysis, and its outer face exhibits a 
conspicuously fibrous texture. Nearly the whole of the outer face of 
the ramus is formed by the dentary («?.), only a very small angular 
('ig.) appearing behind. The coronoid region is obscure, and so is the 
dentition ; bnt there are indications of a series of large teeth on the 
anterior part of the dentary on both sides, and some minute teeth 
within on the left side probably belong to the splenial. The pre- 
operculum [^p. op.), well shown on the right side and partly also on the 
left, is a much-expanded unornamented bone, marked by the con- 
centric and radiating irregularities of growth ; its exposed portion 
does not extend to the top of the cheek. The operculum {op.), nearly 
perfect only on the left side, is trapezoidal in form, widest below, and 
its maximum width slightly exceeding the depth. The bone is not 
flat, but considerably curved inwards postero-superiorly ; and as on 
the preoperculum, the strnctural lines form its only ornament Below 
the operculum there are merely fragments of the other plates, notably 
a few traces of branchiostegal rays on the right side. The left post- 
temporal projects a little out of the matrix behind the cranial roof 
The second specimen in the Enniskillen Collection (Brit. Mus., 
No. P.3709) is very unsatisfactory, but evidently belongs to the same 
species as the above, and shows that the detached pectoral fin (No. 
P. 3709a) is correctly placed here. This fin (pi. xx., fig. 2) is long and 
narrow, with about ten stout rays and others behind, all unarticulated 
for the greater part of their length, but very finely divided distally. 
Some of the stouter rays exhibit feeble transverse wrinkle.^ neur the 
