57 



The Class Ostracophori 



mobranch stock. In favor of this view is the character of their 

 armature, the bony plates themselves to be regarded as formed 

 by the fusion of shagreen grains or scales. According to Tra- 

 quair: "Specialization from the most specialized form, Lanar- 

 kia, has been accompanied by (i) fusion of the spinelets (Lanar- 

 kia) or shagreen grains (Thelodus] into plates, scutes, and 

 rhombic scales, supported by hard matter developed in a deeper 



FIG. 353. 



FIG. 354. 



FIG. 353. Odontotodus schrencki (Pander) (Tremataspis) , ventral side. 



Oesel. (After Patten.) 

 FIG. 354. Odontotodus schrencki (Pander) (Tremataspis) , dorsal side. 



Oesel. (After Patten.) 



Island of 

 Island of 



layer of skin, and (2) alterations in the pectoral fin-flaps, which, 

 becoming covered up by the postero-lateral plates in Drepanaspis, 

 are finally no longer recognizable in the Pteraspida." 



Woodward leaves their exact relationship undefined, while 

 others have regarded them as mailed lampreys, at any rate to 

 be excluded from the Gnathostomi, or jaw-bearing series. The 

 apparent absence of true jaws, true limbs, and limb-girdles 

 certainly seems to separate them widely from true fishes, but 

 these characters are negative only, perhaps due to degeneration, 

 and at any rate they are not yet absolutely determined. Cer- 

 tainly they offer no positive proof of affinity with the modern 

 Cyclostomes. 



