WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 1 65 
P(ic/ii/co?'?nus, however, is still very unsatisfactory, and even the 
foWowiu^ spec ijic dia'^}iosis,c\uei\y based on the material now described, 
must be regarded as only of provisional value : — 
A stout species of moderate size, attaining a length of about 
O om. Head much shorter than in the type species, P. macroj)teriis, 
and this with the opercular apparatus occupying more than one 
quarter of the total length of the hsh ; operculum triangular, deeper 
than broad, and branchiostegal rays about 40 in number. Dorsal 
tin with about 30-35 rays, arising just in advance of the middle of 
the hack : anal fin with about 25 rays, and its origin slightly more 
than twice as distant from the pectorals as from the caudal. Scales 
of moderate size and smooth. 
Pachycormus acutirostris, Agassiz. 
Plate XXL, figs. 2-4. 
1844. Pacliycormm acutirostris, L. Agassiz, Poiss Foss., vol. ii., 
pt. ii., p. 114. 
1895. „ „ A. S. Woodward, Catal. Foss. 
Fishes, B.M., pt. iii., p. 384. 
Type : Imperfect head ; British Museum. 
Some detached heads of Pachycormus from the Whitby nodules 
were named P. acutirostris by Agassiz ; but this species has never 
been defined, and the original record of the name is only accom- 
panied by the brief statement :— " E.spece a museau pointu, a dents 
fines et tres acerees." These fossils not improbably belong to the 
typical species P. macropterus, but in the absence of conclusive 
proof it seems best to retain the name by which they have hitherto 
been entered in catalogues and lists. Their great interest consists in 
the features of cranial osteology they exhibit. 
One of the best examples of these heads in the British Museum 
(No. P. 3705a) is labelled by Agassiz as intended for a type specimen. 
It is shown of the natural size from the left lateral aspect in pi. xxi., 
fig. 2, the gular plate being added in tig. 2a. The bones are much 
fractured and flaked, while most of those of the right side are buried 
or broken away, and the large postero-inferior suborbital is thrust 
forwards. The form of the snout is deceptive, the actual bone having 
