2934 THE ARMORED PRIMEVAL VERTEBRATES 



definite is known with regard to the nature of the nose, mouth, and jaws. 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. Wood- 

 ward 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 favor that supposition; but the discovery of an allied organism in the 

 Devonian of Spitzbergen suggests the wisdom of suspending judgment. The dor- 

 sal 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 armor; 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. ' ' 



