96 DEAN. [Vou. IX. 
the fin-fold of the ancestral vertebrate. The anterior fin- 
margin, like that of the pectoral, is encrusted with denticles 
of shagreen. 
The supports of the ventrals are entirely in accord with the 
primitive disposition of the fin-rays. The basalia, which in 
Xenacanthus and Pleuracanthus have coalesced, are here in a 
condition of concrescence in the anterior root of the fin, duz 
are still separate, one from the other, and are still rod-like, 
homologous in every way with the baseosts of an unpaired fin. 
A still more proximal element has not been determined, but 
it may not unnaturally be inferred, from the very convergent 
nature of the rod-like basalia, that a pelvic cartilage, —if one 
existed, — must have been exceedingly small, representing 
the coalesced axonosts of a paired fin of so azygous a type. 
It is with some doubt that dermal striation is to be observed in 
the ventrals. 
Returning to the view of Smith Woodward as to the 
significance of the fins of Cladoselache, it will at once be seen 
that the discovery of basalia must of necessity modify his 
general conclusions. The concentration of the rays in the 
anterior and median portion of the fin might not imply that 
the process of joint-forming, and of the out-sprouting of an 
‘“archipterygium,” would here take place; it would seem that 
these conditions would rather arise in the regular train of 
evolution exemplified in Xenacanthus and Pleuracanthus. 
Concentration of rays would appear a modification of the 
anterior rim of this primitive fin as a support or cut-water. 
The compressed nature of the fin-rays (z.¢., there appearing to 
be two layers, the tips of the under layer being only seen) 
might, moreover, be regarded as a specialized device for 
strengthening the fin-plate, unless one were to devise an 
unnecessary theory as to the original derivation of paired fins 
from double lateral folds. The primitive character of the 
paired fin, the significance of the radial cartilages, and the 
manifest homology of paired to median fins, the recent material 
shows that Smith Woodward has very precisely indicated. 
Jaekel, on the other hand, has taken a most conservative 
view as to the morphological value of the fins of ‘ Cladodus,’ 
