Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 621 
The head, which has been selected for description, is 2°7 inches in length, 
and the posterior part is 0°9 inch in height. The orbit is 1:3 inch behind 
the anterior extremity of the maxille; it is 0-4 inch across, and is situated 
0-1 inch from the superior outline of the skull. The operculi are large; 
the anterior margins of each are straight, the posterior ones rounded and arched 
towards the abdominal surface of the fish; the pre-operculi occupy the largest 
area, each operculum being a long and narrow bone attached to its posterior 
margin. The branchiostegal rays are small and slender, but long; the actual 
number does not appear, but there were probably eight or ten on each side. The 
superior surface of the skull was protected by strong plates or bones covered 
thickly with enamel, as were also those of the other parts of the head. The 
mandible is 2°1 inches in length, and is articulated to the bones of the skull at a 
point considerably behind the orbit. The mandible is a strong and comparatively 
thick bone, expanding widely towards the median line between the jaws, the lower 
surface bending slightly upwards towards the anterior extremity, whilst the upper 
or alveolar surface is straight. The maxillz are slightly longer, and overlap the 
mandibular bones; the posterior portion is thicker than the mandible. A peculiar 
depression of the anterior extremity of each maxillary appears to be a natural 
one, other specimens indicating the same peculiarity ; both are furnished with a 
large number of moderately-sized, recurved, sharply-pointed teeth. 
The spinal column consists of seventy-two vertebrae: of these fifty-two are 
thoracic, twenty-eight extending from the head to the anterior ray of the dorsal fin ; 
the remaining twenty are abdominal. The anterior vertebre are twice as long 
as high, the articulatory surfaces well ossified, but the intermediate central part 
contracted and small. Opposite the commencement of the dorsal fin the vertebre 
become thicker and shorter ; this character is maintained to the base of the tail; 
but the vertebree decrease in size backwards. The ribs are slender, and bent 
considerably backwards. Neural spines extend from the upper surfaces of the 
vertebree and beyond the abdominal cavity; stronger hemal as well as neural 
spines support the posterior portion of the body of the fish. A number of closely 
impacted strong interneural spines support the dorsal fin. 
The dorsal fin is composed of thirty-eight rays ; the anterior ones are strongly 
jointed and curve slightly backwards; they are 0-5 inch in length. The rays 
gradually diminish in strength backwards, those near the posterior termination 
being not only more slender, but considerably shorter than the anterior ones; the 
basal part of the rays is not jomted, but towards the distal extremity they are, 
and the rays also bifurcate. 
The anal fin consists of fourteen rays and possesses similar characters to those 
of the dorsal fin. 
The caudal fin is moderately expanded and deeply cleft. It is supported by 
twenty-two principal rays; those on the external margins of the two lobes are 
TRANS. ROY. DUB. SOC., N.S. VOL, III. 4P 
