THE DEVONIAN PERIOD. 



483 



The ostracoderms. — The strange forms grouped under this term 

 bear external resemblances in the head and trunk to the trilobites 



Fig. 214. — Restoration of Cephalaspis seen from below. A part of the ventral wal? 

 of the head is shown on the left, the rest being removed to show the inner surface 

 of the roof of the shield. (After Patten.) 



and king-crabs, while some of them have caudal fins and a fish-like 

 body. Because of these last features and the presence of bone cells 





Fig. 215. — Restoration of the head shield of Cyathaspis, showing the oar-like appen- 

 dages, ap, the three median eye-pits, ep, and the paired muscle markings, mm, 

 sometimes regarded as gill-pouches. (After Patten.) 



in the dermal armor of some members of the group, as well as their 

 intimate association with true fishes, they have been classed as fishes 

 until recently. But no vertebrae nor notochord has been found, nor 

 true pectoral or pelvic appendages, nor do they possess either upper 



