Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 585 
‘Threissops formosus of Agassiz. In 1866, Pictet included in this genus a specimen 
obtained from the hard chalk of Hakel. The fish was imperfectly preserved, so 
that the characters of the genus could not be completely identified; but so far as 
could be observed, it agreed in all points with the description given by Heckel. 
The characters which justified the relationship were the form of the pectoral fins, 
composed of very large rays; the operculum was probably denticulated; the 
disposition of the vertebre and their apophyses were similar, as were also the 
large scales, with rounded posterior margin. The author further remarks that the 
only genus which could cause any hesitation is that of Spathodactylus, established 
by Pictet for a fish from the Neocomian (‘‘ Materiaux pour la Paléontologie Suisse,” 
2nd series; ‘‘ Description des poissons des Voirons,” Part u., p. 2, pl.1.). The 
Lebanon fish, tolerably well preserved in the dorsal region, presented no trace of 
the large isolated ray which exists in Spathodactylus. 
Chirocentrites libanicus, Picrrr and HumBert. 
Picrer et HumsBert, 1866. ‘Nouv. rech. sur les poissons fossiles du Mont Liban.,” 
p. 88, pl. xm. 
The fish is large; the example described by the authors cited above was 
imperfect ; the anterior portion of the body only being preserved. The head 
was badly preserved; the remaining part of the body, from the occiput backwards, 
comprising twenty-four vertebra, was 6°5 inches in length; and the total length 
of the fish, if it were complete, is estimated at about 24 inches, that is on the 
supposition that the body was similar in form to that of Chirocentrites coroninii, 
Heckel. 
The vertebre are nearly as high as long; attached to them are neurapophyses, 
the latter robust, oblique, and apparently exhibiting traces of branching apophyses. 
The ribs are preserved only in the upper part; the bones of the trunk are 
considered to resemble in their arrangement and complication the living 
Halecoids. 
The pectoral fins are well preserved, and form the most important feature 
of the specimen described by MM. Pictet and Humbert. The rays of the right 
fin are preserved, and there is also the base of the rays of the left fin. The rays 
of the right fin are very large, more so probably than in any other known species. 
The first ray has been in part covered by the second, and it is difficult to say 
which is the one and which the other. What appears to be the second is longest, 
attaining 2°2 inches; it expands uniformly from the base to the extremity, where 
its width is 0°3 inch. A longitudinal striation divides its surface into two unequal 
parts ; the anterior part, which is the straighter one, presents fine oblique strie ; 
the posterior part is ornamented by longitudinal striz, three or four in number, 
near the base, but branching into a larger number towards the distal extremity. 
