PAL^EOSPOND YL US 



71 



esses. Its skull was highly evolved : in its anterior part 

 were represented, according to Traquair, the palatine car- 

 tilages ; the brain case was complete, and the auditory 

 capsules were of relatively enormous size. The lateral 

 plates of the neck region are as yet uninterpretable. 



From the evidence of Palaeospondylus, accordingly, it 

 may reasonably be inferred that lamprey-like forms existed 

 in highly specialized conditions, even at the beginning of 

 Devonian times. If they then existed, it is of course not 

 impossible, and perhaps even not improbable, that their 

 offshoots may have culminated in the Ostracoderms, as 

 Smith Woodward has suggested. These can certainly 

 belong to no gnathostome stem. Their organs, though 

 often highly specialized, were yet of the most primitive 

 order, — lack of paired appendages,* softness of axial parts, 

 lowly sense organs; even the dermal plates, elaborate in 

 their subdivision or ornamentation, or in the special uses, 

 as "opercula," "pectoral fins," or "fin rays,"t 3-i'e yet but 

 primitive specializations of the exoskeleton. 



* The presence of paired fins in Paloeaspis, as determined by Claypole, has 

 not been confirmed. The present writer, to whom the type specimens were 

 kindly shown by their describer, must regard these structures as elasmo- 

 branchian (Chimaeroid?) spines, in crushed condition, accidentally associated 

 with the head region of the fossil. 



t It is obvious that these structures are but analogous to the opercular and 

 fin structures of fishes, and would tend to separate, rather than closen, the 

 ties of kinship of these groups. 



