Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 471 
where they are round, ‘25 of an inch in diameter, and ‘1 inch in length: they 
are apparently thin bony plates, joined together by cartilage. 
The paired fins are well preserved ; the pectorals are situated immediately 
behind the head; the left fin extends from the body a distance of 2 inches; its 
base is about 1 inch in diameter; its surface is covered with the characteristic 
dermal skin; the fin was probably thin and entirely cartilaginous, because its 
substance is folded, and apparently twisted towards its extremity; the right 
pectoral is imperfect; the right ventral is absent; the left ventral is well pre- 
served ; it is situated 2:4 inches behind the anterior insertion of the pectoral fins, 
and is fully 1 inch across the base ; it extends from the body ‘8 inch. 
Of the vertical or unpaired fins the dorsal is absent; the anal and caudal 
present. The anal fin is situated about midway between the ventral and the 
caudal; it extends 1 inch along the ventral surface of the body; anteriorly it is 
‘6 of an inch in depth, diminishing gradually backwards. The caudal fin is 
4 inches in length, and embraces about seventy vertebra, which extend to 
the extremity of the upper lobe. The base of the tail is ‘6 inch in diameter. 
From this springs the lower lobe, increasing in 1°4 of an inch backwards to 
a depth of 1:1 inch: it is entirely cartilaginous. After the termination of the 
lower lobe the upper one is ‘7 in depth, and gradually diminishes posteriorly, 
and ends in a somewhat rounded extremity. 
This specimen differs so completely in its dental armature from the forms 
described by Pictet, that there can be no hesitation in separating it from them: 
the teeth correspond closely with those of the existing Notidanus, and it is 
therefore placed in that genus with the nomen triviale gracilis. Its nearest fossil 
relationship is with Notidanus microdon, Agass. (Poiss. foss. vol. iii., p. 221, 
pl. xxvur., fig. 1, and Pl. xxxvi., figs. 1, 2). It is distinguished by having only 
five denticles, the largest of which is not serrated, whilst those of N. microdon 
are six in number, and the anterior denticle is serrated along the anterior 
border. The latter is found in the white chalk of Sussex. The specimen of 
Notidanus miinsteri, Agass. (op. cit., p. 222, pl. xxvuz., figs. 2, 3), found by Count 
Miinster in the Jurassic rocks of Streitberg, in Franconia, differs from N. gracilis 
by the rapid diminution in size of the smaller denticles, the fifth being very short; 
and by the shortness of its base as compared with the height of the denticles. 
Formation and Locality.—Upper Cretaceous: Sahel Alma, Mount Lebanon. 
£z coll—tLewis Collection, R. Damon, Esq., Weymouth. 
8T2 
