168 WOODWARD : FOSSIL FISHES OF THE UPPER LIAS OF WHITBY. 
shown by the remains on both sides of the fossil to have been 
flattened, without any strong ridges, and marked only by the fine 
rugose ornament, with certain small radiating canals, which may 
have been either sensory or vascular. The left preoperculum, repre- 
sented in the figure, is much flaked, exposing an extensive impression 
of its inner face. No interoperculum is visible, and it must have 
been relatively small if ever present. The two uppermost branchios- 
tegal rays {br,) are considerably larger than the others. The series 
is too imperfect for counting, but the fine external ornament is 
observable on all of them. The gular plate is also displaced and 
fractured, though evidently of the usual large proportions. Behind 
the skull and above the operculum may be seen remains of the supra- 
temporal and supraclavicular plates, the latter element very deep and 
narrow. There are also finely rugose scales beyond these bones, 
nearly all slightly deeper than broad in their exposed portion. 
Another specimen IdhoHQd. " Pachyconnus aciitirostris, Agass." 
by Agassiz (No. P. 3705b) is more imperfect than those just described, 
but interesting as exhibiting the jaws and teeth in a somewhat better 
state of preservation. Those of the left side are shown of the natural 
size in pi. xxi., fig. 3. The supramaxilla (s. mx.), preserved in its 
natural position on the right, slightly displaced on the left, is an oval 
plate of bone, three times as long as its maximum depth, and marked 
externally with a very fine rugose ornament. It overlaps the maxilla 
{mx.), which is exposed in a narrow strip beneath and exhibits the 
same ornamentation. This bone appears to have been a little more 
than three times as long as the supramaxilla, and it gradually tapers 
forwards from the anterior end of the latter element. Its small 
conical teeth are smooth and slightly incurved, and the series on the 
right side is shown to extend backwards just beyond the point of 
overlap of the supramaxilla. The premaxilla is unfortunately w^ant- 
ing on both sides. The mandible, though much fractured, is best 
preserved on the left, and the anterior half of the dentary {d.) bears 
a close series of teeth similar to those of the maxilla, but somewhat 
larger than these. It may also be added that some of the small 
equilateral scales behind the branchiostegal rays are well preserved 
in this specimen, and are very finely marked with a rugose ornament 
in their exposed portion. 
