498 Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 
a flattened wing-like expansion on each side. The interhzemal spines are similar 
to the interneural, excepting those placed most anteriorly, which are much more 
numerous in proportion to the hemal spines. The caudal portion of the body 
is separated from the abdominal by a strong rounded bone, with the concave 
surface towards the abdominal cavity, and extending to and supporting the long 
anterior rays of the anal fin. The ribs are strong, and extend to the abdominal 
surface of the body. 
The dorsal fin extends from the base of the tail to the highest point of the 
back, and increases in size anteriorly. The length of the rays and their precise 
character is not apparent, but they were probably 1:5 inches in length at least, 
and gradually decreased nearer the tail. ‘The anal fin is similar to the dorsal, 
but does not extend so far forwards. The caudal fin, as already observed, is 
short, but the two lobes are widely expanded. The upper lobe consists primarily 
of nine rays; these dichotomize and towards the extremity are again divided and 
are jointed transversely. The lobe of the tail is not all exposed, but it is at 
least 2 inches in length. The median rays of the tail, eighteen in number, are 
supported from the inferior surface of the concluding caudal vertebrae; they 
are 0°5 inches or more in length. The lower lobe is composed of eight fin-rays, 
the longest of which are slightly more than 2 inches in length. The anterior 
rays of both the upper and lower lobes are supported by a series of imbricating 
rudimentary rays. 
Of the paired fins only the pectoral is visible. It is situated immediately 
behind the opercular apparatus, and is attached to a large pectoral arch. It is 
about one-third the height of the fish above the abdominal margin. The fin 
consists of a large number of small fin-rays, the longest about an inch in 
length. 
The body and head of the fish appear to have been covered by thick plates 
and scales. Patches still remain, but the greater part has been removed. ‘The 
scales have already been mentioned on a previous page, along with Sir P. 
Egerton’s description of the peculiar articulation of the scales, one with another, 
in the Pyenodontidz. On the ventral surface beneath the pectoral fin the scales 
are 0-4 inch in length and 0°2 inch in breadth. A thick rib extends longitudinally 
across the scale and splices with similar ribs on the scales above and below. 
In the specimen figured (Pl. xxi, fig. 1) a number of the thickened portions 
of the scales remain, whilst the thinner portion has disappeared; the result is 
that a series of lines of bony substance is preserved, extending from the dorsal 
surface diagonally backwards across the apophyses of the vertebre, the vertebral 
column, and towards the abdominal surface. 
This species may be readily distinguished from those described by Agassiz 
from the Solenhofen beds, by the rounded and slightly elongated form of its 
body. It approaches most closely to Microdon elegans, Agassiz; but the size 
