P TERA SPIDOMORPHI 



199 



front, and a sharp median spine and two lateral angles behind (Fig. 170). 

 This shield appears to be made up of seven plates, distinct only in the 



A. 



Fio. 170. 



A, dorsal view of the shield of Pteraspis rostrata, showing the openings of the lateral-line 

 system. B, transverse section (after Patten). C, ventral view of the same, with the ventral 



lit-st.. ration of l'trraf)>ix rostrata, Ag. ; Lower Old Red Sandstone. (After A. S. Woodward, 

 Brit. Ma.-: I'ntnl.) Left-side view ; the tail and fin only in outline. 



young. The rostral plate surrounds a preoral projection, two orbital 

 plates are pierced with holes which presumably harboured the eyes, a 



