57° 



The Class Ostracophori 



nil ibrancli 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 fonn, Lanar- 

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

 kia) or shagreen grains {Thelodns) into plates, scutes, and 

 rhombic scales, supported by hard matter developed in a deeper 





Fig. 3.53. 



Fig. 354. 



Fig. 353.— 0(^o?itotodi(s schrencki (Pander) (Tremalaspis), ventral side. Island of 



Oesel. (After Patten.) 

 Fig. 354.—Odontotodtis schnncki (Pander) (Tremataspis) , dorsal side. Island of 



Oesel. (After Patten.) 



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

 becoming covered up by the postero-lateral plates inDrcpanaspis, 

 are finally no longer recognizable in the Pteraspidw." 



Woodward leaves their exact relationship undefined, while 

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

 be excluded from the Gnatliostoini, 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 modem 

 Cyclostomes. 



