FISHES OF THE CHALK. 
135 
polish : several vertebrae are imbedded in the chalk 
near its base. 
A magnificent specimen of a dorsal fin, or radius, 
of a fish allied to the Balistes, is one of the most 
interesting productions of the Upper chalk in my 
collection. It was unfortunately broken by the 
quarry-men, and the intermediate portion de- 
stroyed. 
It consists of thirteen narrow parallel rays, divided 
by fine sulci, that gradually diminish in size as 
they approach the apex, which is broken off. The 
rays are anchylosed, or united to each other, the 
grooves or furrows penetrating but a short distance 
into the substance of the fin. Tlie upper edge is 
serrated, having fifteen obtuse projections, with 
corresponding depressions. The inferior margin 
is entire, and near the base of the fin is furnished 
with numerous slender processes, or cirri, that oc- 
cupy a space of three inches in length and an 
K 4 
