PALAEOSPOND YL US 



57 



has been suggested that the pectoral fins are represented by the large 

 postbranchial plates mentioned above. The histological character of the 

 skeleton is quite unknown, but it was probably cartilaginous. 



Many views have been put forward with regard to the affinities of 

 Palaeospondylus (Traquair, Gill [166], etc.). That it is not a larval form 

 seems to be proved by the presence of well-marked centra. This fact is 



FIG. 38. 



Palaeospoiulylus Gunni, Traq. ; from the Middle Old Red Sandstone of Caithness; restored. 

 (After R. H. Traquair, from Brit. Mus. Guide.) 



also a very serious objection to its close association with the Cyclostomes. 

 While the fin-rays and the apparent absence of paired fins recall the latter, 

 the structure of the vertebral column, the skull, and the visceral arches 

 approaches that of the Gnathostomes. To which of these two Branches 

 Palaeospondylus belongs it is not yet possible to determine ; it may have 

 arisen from an extinct intermediate group. 



PalaeQspondylus, Traqnair ; Middle Old Red Sandstone, Caithness. 



