162 WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 
1844. Pachycormus latus, L. Agassiz, ihid., pt. ii., p. 114. 
1 843-58. Fachycormus curtus, F. A. Quenstedt, Flozgeb. Wurtemb. , 
p. 244 ; Der Jura, p. 235, pi. xxxii., 4. 
1860. Pachycormus curtus, A. Wagner, Gelehrt. Anz. k. bay. Akad. 
Wiss., vol. 50, p. 225. 
1895. Pachycormus curtus, A. S. Woodward, Catal. Foss. Fishes, 
B. M., pt. iii., p. 385. 
Type ' Imperfectly preserved fish from Whitby ; British Museum . 
Remains of the true and typical Pachycormus itself are tolerably 
common in the Whitby Lias, and four species were recognised by 
Agassiz. Only one of these species, however, has hitherto been des- 
cribed, and even the original diagnosis of this form is in many 
respects inadequate and misleading. It is named Pachycormus 
curtus in reference to its comparatively shortened head and trunk, 
and the type specimen is preserved in the counterpart halves of a 
nodule now in the British Museum. 
This fossil, numbered P. 464 and P.3698, represents a fish about 
0'27m. in length. The general form and proportions of the trunk are 
shown by the margin of the squamation ; but the abdominal region is 
a little deepened by crushing, as indicated by the displaced scales in 
front of the dorsal fin and behind the pectorals. The skull is a little 
deflected to the left, so that the remains of the cranial roof are shown 
on the side figured by Agassiz {loc. cit.), while an imperfect supra- 
temporal (or perhaps post-temporal) is seen above the opercular bones. 
The latter are much fractured, and no distinction is made between 
cracks and sutures in the figure. The operculum is best shown on 
the counterpart ; it is triangular in form, with rounded postero- 
inferior angle, and its maximum depth only slightly exceeds its 
greatest width at the base. The suboperculiim is more obscure, 
but seems to be two-thirds as deep as the operculum ; and there are 
traces of branchiostegal rays below. The original description of the 
trunk is evidently based on Dinkel's misleading figure. The few 
remaining neural and haemal arches are much more slender than 
indicated, as also are the supports of the anal fin, which are shown 
by other specimens to be equal in number to the dermal rays. All 
these elements exhibit their usual hollowness in the fossil, having 
