636 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 22, 
most protuberant at the muzzle; behind, it is angulated near the centre, 
the posterior margin of the operculum (s) determining the form ; the 
jaws (p,q) are nearly perfect, and are closed, showing that the mouth 
shuts upwards; the maxilla is wanting, only the impression of it 
remaining, indicating its form and position. The brow, orbit (x), 
gill-cover, and clavicle (rv) are all in their natural positions, no con- 
sider able disturbance of these parts having taken place. 
The pectoral fin (¢), though in disorder, occupies its proper situation 
immediately below the angle of the operculum, near the longitudinal 
centre ; and one of the ventral fins (¢) is well displayed at the ventral 
margin in connexion with the lower extremity of the clavicle. It 
is narrow, and its pointed extremity mclines backwards as far as the 
posterior extremity of the second ventral or thoracic plate; it is 
upwards of half an inch in length. Little more than half an inch re- 
mains of the elongated portion of the dorsal fin (a); and mere traces 
are perceptible of the narrow posterior division. The narrow back- 
ward portion of the anal fin is scarcely distinguishable ; but the large 
anterior member ((), though not entire, is distinct about the middle of 
the ventral margin and a little behind the ventral plates. The tail- 
fin is almost perfect, exhibiting both the general outline with the 
lobes spread and the surface-characters. The upper lobe, which isa 
little longer than the under, is about an inch long. 
The transverse series of plates and rods are much disturbed over 
the whole surface, though in places they are partially in order and 
show the same surface-characters as are displayed in specimens in 
which these parts are more perfect ; and, as in them, they are covered 
with black enamel-like matter. The ventral plates (m), however, are 
arranged in complete order along the ventral margin, from the base 
of the ventral fin to a little in front of the anal, overlying each other 
apparently forwards; but on closer examination they are seen to 
imbricate backwards, and to give off from their upper extremities the 
peculiar compound columns (7) already described, which, extending 
upwards in parallel order, incline towards the head. The anterior 
ones are the shortest, and appear to terminate near to the margin 
of the clavicle. A few of the posterior pass above the angle of the 
operculum and can be seen to join with the lateral plates of this 
region, notwithstanding that they are much disturbed. The large 
posterior abdominal rods (0) occupy their usual position, sloping 
backwards from the last ventral plate. 
The specimen (P]. XLIII. fig. 2) next to be described is highly 
instructive, though it isin many parts much disarranged. The head, 
in particular, has greatly suffered, the upper margin being entirely 
obscured by the opercula(s), which have been torn from their natural 
positions and turned upwards and forwards ; their lower extremities 
are placed close together, and project in front of the brow. They lie 
with the external surface uppermost, their anterior margins approxi- 
mating. That belonging to the right side has carried along with it 
the pectoral fin (c), which is beautifully displayed, in an expanded 
state, almost complete. The left pectoral is distinctly seen in its 
natural position, though much injured, and overlain bya thin film of 
