554 Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 
spinous bones. The rays are strong; anteriorly they are 0°45 of an inch in 
length, and decrease backwards to half that length; the rays were probably 
longer than the part preserved, the basal portions only, which are not divided by 
articulation, remaining, whilst the distal extremities, which were probably articu- 
lated, have been separated and lost. The anal fin is 1°5 inch behind the ventrals, 
and its base extends 0°5 of an inch, approaching to 0°3 of an inch, to the caudal ; 
it is composed of ten rays; the anterior one is 0°8 of an inch in length, the others 
decreasing in length backwards. The distal half of each is divided by a number 
of articulations, the proximal one, like those of the dorsal fin, being unbroken by 
articulations. 
Only the external rays of the lower lobe of the caudal fin are preserved; they 
are 1:5 inch in length, strong, and articulated at short intervals. A number of 
rudimentary caudal rays support the fin. 
The pectoral fin, consisting of ten rays, the longest of which is 1:0 inch in 
length, is situated immediately behind the gill cover, opposite to the anterior rays 
of the dorsal, and about 0°3 of an inch above the abdominal margin of the body. 
The ventral fins are placed 1:1 inch behind the pectoral, joining at the abdominal 
line; they are 0:9 of an inch in length, and consist of eight rays each; the fins 
are attached to a triangular pair of bones, meeting internally in the axis of the 
fins. The ventral fins are opposite the median portion of the dorsal fin. The 
rays of both the paired fins are simple for half their length; the remaining portion 
is divided by joints. 
The scales are large, 0°2 of an inch in height, with semicircular posterior 
outline; they are thick and, where well preserved, appear to be coated with 
ganoine; this is more especially so with the external bones of the head, which 
have a decidedly enamelled and glistening surface. 
This species is apparently most nearly related to Istieus macrocephalus, Agass. 
It may be distinguished by its greater height as compared with the length, and 
the larger size of the head; the head of I. macrocephalus occupies a quarter of 
the length of the fish, in this species it is little more than one-third. The dorsal 
fin in the example now described commences at a point considerably nearer the 
head than in I. macrocephalus, and it also terminates posteriorly at a greater 
distance from the tail. The anal fin of I. macrocephalus is supported by twelve 
rays; in this one there are only ten. 
Formation and Locality.—Upper Cretaceous: Sahel Alma, Mount Lebanon. 
Ex coll——Robert Damon, Esq., Weymouth. 
