FINS OF ELASMOBEANCHS. 443 



ating in part from its distal end. Tlie 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 smaU 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 prea.xial fin-rays over the more postaxial ones. 



NOTIDA.NUS CINEREUS. 



Dorsal Fin (Plate LXXV. 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 (b). 



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 sm-all 

 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. 



