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 



D. 



Fig. 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 

 shield, v. D, enlarged surface view of the shield of Palaeaspis. E, enlarged view of the course of 

 the lateral-line canal below the surface in Palaeaspis. bo, opening, possibly branchial ; d, dorsal 

 plate; e, orbit; I, lateral plate; 0, orbit; op, opening of lateral-line canal; p, position of 

 internal pineal pit ; r, rostral plate ; s, spine ; v, ventral plate. 



Fig. 171. 



Restoration of Pteraspis rostrata, Ag. ; Lower Old Red .Sandstone. (After A. S. Woodward, 

 Brit. Mas. Catal.) 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 



