No. 430.] PAIRED LIMBS OF VERTEBRATES. 769 
each with a corresponding basal; unlike cladoselachids, there 
are no intercalated rays. Next ancient is Traquair’s specimen 
of Cladodus (Lower Carboniferous) (cf Fig. 1), whose pectoral 
gives evidence of a line of basal plates extending backward like 

T T 
Fic. 1. — The Paleozoic shark Cladodus neilsoni Traquair. The fossil is shown surrounded 
mtem e teme f Cladoselache of of similar size, — indicating that the fins of 

a rayless axis of an “archipterygial’’ fin. This specimen has 
been taken in evidence of the non-primitive nature of the fin- 
fold type of limb (vide infra). Last of the ancient forms are 
the Permian symmoriids and xenacanthids. Of these Symmo- 
| Tium, judging from the single fragmentary pectoral described 

