PLACOGANOIDEI. 



145 



their appendages, the rays 

 of a "dorsal" and "anal" 

 fin ; and, by the analogy of 

 Cephalaspis, the tail was 

 most probably terminated 

 by an unequal-lobed fin. 

 The lower jaw is composed 

 of two rami, loosely con- 

 nected at the symphysis; 

 so that, being displaced in 

 crushed fossil specimens, 

 they gave the notion of the 

 fish being provided with 

 laterally-moving jaws, like 

 those of the lobster. But, 

 the lower jaw worked verti- 

 cally upon a fixed upper 

 one ; both jaws being pro- 

 vided with from ten to 

 twelve teeth on each side, 

 anchylosed to the bone. 



An under-view of the 

 cephalothoracic buckler of 

 Coccosteus is given in fig. 62, 

 shewing the internal sur- 

 face and sutures of most of 

 the cephalic plates, and the 

 external surface of the plates 

 of the plastron. 9, rostral 

 plate ; 7> premedian ; 5, me- 

 dian ; 8, prelateral ; 6, late- 

 ral; 16, and ^\, the suborbital 

 bone ; 15, preventromedian ; 

 behind the lozenge-shaped 



