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Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 
Osmeroides gracilis, Davis. 
(PL. xxx, figs. 2; 3:) 
Several specimens of this graceful fish have been discovered in the cretaceous 
beds at Sahel Alma. The example figured exhibits many of the details of the 
structure and characters of the fish. From the snout to the base of the tail 
the length is 8°5 inches, of which the head occupies 2°7 inches; the caudal fin 
adds 2:0 inches to the length. The height of the body in front of the dorsal fin 
is 16 inch; the peduncle of the tail is 0°6 of an inch. 
The head is half as high as its length. The orbit is situated anteriorly, rather 
high, 1:2 inch from the snout; it is small, the cranial bones and infra-orbital 
ring are well developed. The operculi are large, and extend with a well-rounded 
and prominent posterior margin towards the abdominal surface of the fish. The 
jaws were long, and apparently capable of wide expansion; the teeth cannot be 
distinguished. The snout is not well preserved in this specimen; but another 
(Pl. xxx1., fig. 3) exhibits the structure of the under surface of the head remark- 
ably well. The lateral margins of the mandibles converge anteriorly in a more 
or less triangular form; between the jaws there is one or more plates, and behind 
these the branchiostegal rays: the latter average one inch in length, and number 
eight on each side; those on the right side overwrap the opposite ones to a 
slight extent, the breadth of the whole being slightly more than an inch. The 
posterior extremities of the branchiostegal rays extend to the scapular arch, which, 
on the abdominal surface, curves considerably forward. In a third specimen 
the alveolar surface of the jaws exhibit the orifices, where teeth, apparently of 
considerable size, but deciduous, have been implanted. The opercular and other 
bones of the head are coated with a thick enamel, on which there are raised 
lines radiating from the upper anterior margin. 
The vertebral column is composed of sixty-three vertebra, of which twenty 
are caudal and the remaining forty-three abdominal. In the abdominal region 
the vertebre are longer than deep; those of the caudal are deeper than long, 
these are also larger and stronger than those of the anterior part of the body. 
The ribs are fine, and extend backwards a considerable distance beyond the 
ventral fins. The hemal spines are strong, and especially well developed from 
the four or five vertebree nearest the tail; the neural spines are similarly strong 
for the support of the caudal fin; anteriorly they are long, divided at the base, 
and slender; the interneurals, supporting the long dorsal fin, are thick and strong, 
but short and tapering, apparently less numerous than the rays of the fin. Inter- 
hemal spines support the anal fin. 
The dorsal fin is placed on the anterior portion of the body, separated from 
the head by a distance of 1:7 inch, and from the tail by 3°2 inches; its base 
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