No. 1.] MORPHOLOGY OF CLADOSELACHE. gI 
Smith Woodward? has reviewed the origin of the paired 
fins in the light especially of the more recent work in palae- 
ontology. He derives them from the crowding of the fin- 
supports at two definite points, with a tendency towards the 
contraction of the base of the fin to its narrowest limits, with 
a subsequent broadening out of the basal portion to become in 
the pectoral tribasal or polybasal. It is interesting that he has 
taken the fin of Cladoselache into especial account, regarding 
it as exhibiting one of the least modified conditions of the 
exoskeleton of the lateral fin-fold that can be expected in any 
fish in which this fold is already subdivided into its ordinary 
two remnants. In the pectoral “no fin-basals can be detected 
with certainty in any of the specimens the writer has ex- 
amined; and none of the cartilaginous rods that support the 
fin-membrane are transversely jointed. The most singular 
feature of the fin consists in the evidence it affords of that 
crowding and concentration we have already observed in the 
differentiated median fins of the earlier fishes. Between the 
extremities of the unaltered parallel bars there are the rem- 
nants of similar bars that have evidently been reduced and 
displaced by growth pressure. Most of the cartilages bifurcate 
a little distally, but that is a minor matter. The segmentation 
of the rays, the persistence of one of the middle rays, with 
the concomitant partial fusion of the still further crowded and 
reduced bordering rays, would soon, in the writer’s opinion, 
result in the ‘archipterygium’ of Gegenbaur. It is, more- 
over, significant that the anterior (preaxial) rays are much 
more robust than the posterior (postaxial) rays, exactly as in all 
known examples of ‘archypterygium.’”’ 
In this interpretation, however, Smith Woodward is opposed 
by Jaekel, who had also examined the specimens in the museum 
of Columbia College. ‘There is no doubt that the outer 
clearly-marked fin rays take their origin and diverge from 
an inner basipterygoid.” These rays, he continues, have been 
mistaken for the supports of an older continuous fin fold. 
The pectoral fin characters are rather to be reduced to the 
type of Xenacanthus; it is but a Convergenzerscheinung of a 
bottom-living Selachian. The fins, like those of Xenacanthus, 
