354 



THE OSTRACODERMS. 



trabecule. They correspond roughly with the areas in Limulus where the bony 

 trabeculse are most highly developed. (Fig. 205.) In Tremataspis, Cephalaspis, 



B' 



Fig. 232. — Restoration of Cephalaspis. A, From the side; B, from the ha?mal surface. Based mainly on 



C. murchisoni. 



and Thyestes, these areas are covered with loose, superficial, polygonal plates 

 which may, and usually do, fall out, leaving sharply defined, shallow openings 

 in the outer layers. (Figs. 235, A, 236, B.) They have a floor consisting of 



