OUR FACE FROM FISH TO MAN 



vertebrates (Figs. 4, 57). Such food habits would 

 seem reasonable both for those ostracoderms, like 

 Pteraspis (Fig. 4D), which had narrow mouths 

 placed below a long rostrum and therefore adapted 

 for feeding in the mud, and for those like Tremat- 

 aspis (Fig. 4B, C) in which the fore part of the 

 body was flattened into a broad rounded shovel 

 and the mouth was a wide slit-like opening at the 



Fig. 58. Swift-moving Ostracoderm from the Silurian 

 OF Norway (after Kiaer). 



For details, see p. xxv. 



front border of the head. In Cephalaspis (Fig. 



57B) also the mouth appears to have been in 



series with the gill-arches. 



But there were still other ostracoderms of the 



order Anaspida (Fig. 4A), in which the body -form 



seems adapted for swift movement through the 



water and in which the mouth, while not too large 



to be powerful, was strengthened by a bony strip 



with a knob on its front end. Such ostracoderms 



may have already embarked on the career of 



96 



