570 Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 
of the length of the fish, that is 0°6 of an inch; the height is 0°5 of an inch; it 
is triangular in outline, with a rounded posterior margin formed by the gill covers. 
The operculi are convex behind, and have a corresponding concave margin in 
front; they are elongated, but do not exhibit the constituent parts with sufficient 
clearness for identification. The orbit is placed anteriorly, and of small size; 
the maxillary and intermaxillary bones exhibit no traces of teeth; they form an 
acute angle with the line of the cranium. The mandibles are 0°45 of an inch 
in length, and extend slightly beyond the intermaxillary bones, giving prominence 
to the lower jaw, but not nearly to the same extent as depicted in the elongated 
head of O. gracilis (op. cit., see also ‘‘ Poissons fossiles du M. Liban.,” by Pictet, 
1850, pl. 11., fig. 2, where the fish is named Mesogaster gracilis). 
The spinal column consists of fifty-eight vertebra; they are short, but deep ; 
of this number twenty-six are caudal. The ribs are numerous, curved, and 
excessively fine; the neural and hemal spines have triangular apophyses attached 
to the vertebr; they extend at a corresponding angle diagonally towards the 
dorsal and ventral surfaces. The posterior termination of the tail is turned up 
towards the upper lobe of the tail ; this may, however, be an accidental circum- 
stance. 
The dorsal fin is supported by ten interneural spines; there is about an equal 
number of rays to the fin, the longest being 0°3 of an inch in length. The anal 
fin has its origin slightly in the rear of the dorsal, at a distance of 0-7 of an inch 
from the caudal; it is supported by a number (about eight) of interhemal rays; 
the anterior rays of the fin are long, and, compared with the remainder, they 
are very strong. 
The caudal fin is deeply cleft; the termination of the vertebrz is prolonged 
to the upper lobe; the fin-rays are strong and extend 0°5 of an inch; the lobes 
of the tail are 0°6 of an inch apart. 
The pectoral fins are attached to the scapular arch at a point apparently very 
near the ventral surface of the body; the rays extend 0-2 of an inch; their number 
is not determinable. The ventral fins are situated almost midway between the 
pectorals and the anal fin, but they are slightly nearer the pectorals; the one 
exposed contains fourteen or fifteen fin-rays, 0°15 of an inch in length; they are 
supported by pelvic bones, having the form of an elongated triangle. 
Some of the characters which distinguish this species from the type species 
of Pictet and Humbert have been already pointed out. It is shorter and thicker ; 
its head, in proportion to its height, is only half the length of O. gracilis, and 
the lower jaw is not so prominent. The fins also are considerably modified, and 
the anal occupies a position further behind the anterior rays of the dorsal in 
this species. 
Formation and Locality.—Upper Cretaceous: Sahel Alma, Mount Lebanon. 
£x coll—R. Damon, Esq., Weymouth. 
