Davis— On the Fossil Fishes of the Chalk of Mount Lebanon. 619 
Genus. Leptotrachelus. Von per Marck, 
‘ Fossile Fische, Krebse und Pflanzen aus dem Plattenkalk du jungsten Kreide in 
Westphalen,” Paleeontographica, vol. xi., p. 59, 1863—64. 
Body long, narrower anteriorly than behind. Dorsal fin short, sub-median ; 
anal short, probably midway between the dorsal fin and the caudal; ventral 
fins situated under the dorsal. Five series of scales (three according to M. von 
der Marck), of which one is dorsal, and two on each flank; the scales are, in most 
cases, tricuspid, but occasionally heart-shaped (Pictet and Humbert, “ Nouv. rech. 
s. les poiss. foss.,” p. 93). The above diagnosis will require further modification, 
so that the sixth row of scales extending along the abdominal surface may be 
included. 
This genus was instituted by Dr. W. von der Marck, and included one species, 
L. armatus, from the chalk formation of Westphalia. He regarded the genus as 
nearly related to Dercetis, Ag., and it was considered as a Ganoid along with 
the genus Pelargorhynchus, which, in addition to the dermal scutes of Lepto- 
trachelus, possessed small scales and a well-developed dorsal fin. 
MM. Pictet and Humbert discuss the zoological position of the genus at con- 
siderable length, and arrive at the conclusion that it is closely related to the 
genus Eurypholis, Pictet, which has undoubted affinities with the Teleosteans. 
They therefore consider these genera along with Sauroramphus, Heckel ;* Der- 
cetis, Agassiz; Ischyrocephalus,t Von der Marck; and Plinthophorus, ¢ Giinther, 
as forming a natural group, which they are convinced should be considered 
as a sub-class of the Teleosteans, and for which M. Pictet has established the 
family Hoplopleuridz. 
In 1850, M. Pictet described three species of Dercetis from the soft chalk of 
Sahel Alma. The examples described were in a more or less fragmentary 
condition. During the interval intervening between the publication of the 
memoir in 1850 and the “ Nouvelles recherches” in 1866, it was found that two 
of the species, viz. Dercetis triqueter and tenuis, were portions of fishes of the 
same species, and that combined they belonged to the genus Leptotrachelus, and 
are described as L. triqueter. The remaining species, Dercetis linguifer, Pictet, 
was retained by MM. Pictet and Humbert. The example on which it was 
established is a small fragment about 2 inches in length from the body of the 
fish, and exhibits a portion of the spinal column and a few of the dorsal scutes. 
Since the year 1866 a considerable number of specimens have been obtained, 
and, as will be seen from the following observations on the species, they differ 
* Heckel, ‘‘ Beitriage zur Kenntniss der Fossilen Fische (Esterreichs,” 1849, p. 17. 
t Op. cit., p. 60. 
+ Giinther, ‘‘ Geological Magazine,” 1864, vol. I, p. 114, pl. vr. 
