FINS OF ELASMOBRANCHS. 443 
ating in part from its distal end. The most postaxiad ray is the shortest, and has a 
broad and short root-segment. The next two, if not three, rays are connected with the 
metapterygium through the intervention of a small cartilage, broader than long, which 
seems to represent the basal ends of these cartilages coalesced into one small piece. 
The series of segments which continue postaxially the terminal segments of the most 
preaxiad rays, do not extend throughout the whole of the limb, but get smaller and 
smaller postaxiad till they are quite minute. They are all truncated distally, except, 
as before said, the two most preaxial. The more preaxial segments of the distal 
series are each attached not only to the truncated distal end of the penultimate seg- 
ment of their own ray, but also to the preaxial side of the penultimate segment of 
the ray next postaxiad. The more postaxial segments of the same series are also 
so connected; but as here the penultimate rays are not truncated but end distally 
in a point with a short facet on each side, it comes about that the most postaxiad 
terminal segments appear rather wedged in, and equally divided between, the distal ends 
of the two contiguous penultimate segments, instead of appearing specially attached to 
one of them. ‘The arrangement and proportions of these cartilages cause the skeleton 
of the limb to extend distally to a somewhat greater extent towards its preaxial than it 
does towards its postaxial side, though this predominance is much less than the pre- 
dominance of the more preaxial fin-rays over the more postaxial ones. 
NOTIDANUS CINEREUS. 
Dorsau Fin (Plate LXXYV. fig. 2). 
The cartilaginous skeleton of this fin consists of a series of nineteen radials, consider- 
ably and somewhat irregularly segmented, the whole being attached proximally to one 
deep and antero-posteriorly elongated cartilage (4). 
The most preaxiad of the radials, or rays, is very short, and unsegmented. The second 
ray consists of two, and almost all the rest consist of three, segments, whereof the 
deepest is in each case the largest. The four most postaxiad rays consist of but two 
segments each ; but then they are all attached to one considerable supporting cartilage, 
which has all the appearance of being formed of each of the deepest segments of the 
four rays combined together into a single cartilaginous plate. 
The long basal cartilage is convex ventrally and nearly straight dorsally, with small 
concavities answering to the bases of the several radials. This basal cartilage certainly 
corresponds in position, and more or less in shape, to such a structure as would be 
formed by the coalescence of the whole series of basal cartilages in a fin consisting of 
three superimposed series of parts like that of Mustelus antarcticus. 
The whole cartilaginous dorsal-fin skeleton is in this fish placed at a great distance 
above the axial skeleton, the fibrous membrane between the two being almost equal in 
depth to the whole cartilaginous mass. 
