Davis—On the Fossil Fishes of the Chalk of Mount Lebanon. 485 
Rhinobatus latus, Davis. 
(Pl. xvi.) 
The central portions of the body of this specimen are admirably preserved, 
but, unfortunately, the anterior portion of the head and the tail are wanting. 
The whole of the body and fins are covered with minute dermal ossicles, 
closely impacted, more or less rectangular in form, smooth and shining. The 
entire length preserved is 10°5 inches: of this from the pectoral arch the 
head takes 3:5 inches; between the pectoral and ventral arches 2 inches, the 
remainder behind the ventral arch. The head, exclusive of the fins, is 4 
inches across; the thoracic cavity 3 inches. The distance between the two 
extremities of the pectoral fins 7°8 inches, between those of the ventral fins 
4 inches, and the diameter of the base of the tail is 2 inches, gradually 
diminishing backwards. 
The spinal column is well indicated, forming the median axis of the body. 
The total number of the vertebrz preserved is seventy-five: of these twenty-two 
connect the pectoral with the pubic arch and the remainder behind; in the 
posterior part there are twelve vertebrze in the distance of 1 inch; their diameter 
across the articulating surface is 0°17 of an inch. ‘There are twenty-five ribs 
on each side, of which about one-third extend behind the ventral arch. The 
caudal vertebree support lateral spines, which are longitudinally connected by 
bony or cartilaginous processes. 
In addition to the number of vertebree already given it is probable that a 
continuation of the column, about three-quarters of an inch in length, extended 
to the head, but it is covered by the support of the branchial apparatus. 
The head is large: its structure cannot be easily identified. The snout 
probably extended about 1-5 inches beyond the part preserved, and by continuing 
the marginal lines of the head forward the form indicated appears to have 
been nearly a right-angled triangle, the extremity more or less pointed. The 
mouth is not exposed; the surface exposed appears to be the upper one, so that 
the mouth is hidden beneath. The branchiostegal rays, five in number on 
each side, were strong and thick, about an inch in length, their form being 
impressed on the supervening cuticular covering; a largely expanded mass of 
bone or ossified cartilage is exhibited between the branchiostegal rays on the 
median line. 
The scapular or pectoral arch is formed by divaricating osseous plates, 
supported by strong bones connected with the vertebral column. The pectoral 
fin is supported by sixty rays: the median ones being 2°8 inches in length, 
frequently jointed, and increasing in number towards their distal extremities. 
The length of the base of the fin is 5 inches; the fin has a somewhat triangular 
TRANS, ROY. DUB. SOC., N.S. VOL, I. 3X 
