EXTINCT ARMOURED FORMS. 
557 
The arrangement of the median fins is generally similar to that obtaining in 
the second family. With regard to the true nature of the pectoral appendages. 
Mr. Woodward writes that they are commonly considered “ as homologous with 
the paired pectoral fins of fishes, and certainly in their mode of fixation to the 
trunk there is much to favour that supposition; but the discovery of an allied 
organism in the Devonian of Spitzbergen suggests the wisdom of suspending 
judgment. The dorsal body-shield of the latter is simpler than that of 
Pterichthys , but the arrangement of the plates on the ventral aspect is identical, 
and there are also hollow pectoral appendages. These appendages, however, are 
merely simple triangular spines, firmly fixed by suture to processes of the body- 
armour ; and if they are an inferior or special condition of the ordinarily movable 
arms, it seems not unlikely that those arms will prove to be different in origin 
from the paired limbs of fishes.” 
