CROSSOPTERYGII. 



75 



similarly, a considerable development of membrane- bones on the roof of the 

 mouth. The shield of the cranial roof is divided by a much-pronounced 

 transverse suture into a small frontal, and relatively large parietal portion, 

 the former excavated on each side at the upper border of the orbit. The 

 parietal portion of the shield consists chiefly of a long, narrow pair of 

 parietal bones (pa.) extending its whole length, flanked by a pair of squa- 

 mosal elements (sq.) in the hinder half, and by a pair of postfrontal plates 

 (p.f.) in advance of these. The posterior half of the frontal shield is 

 formed by the frontals (/.), which meet in the middle line without a 

 median (pineal) foramen. The orbits (or.) are remarkably far forwards. 

 The plates over the ethmoid region are irregular, apparently more or less 



Fio. 57. 



Rhizodopsis sauroides ; outline restorations of head and opercalar apparatus 

 from the lateral (A), superior (B), and inferior (c) aspects, about one-half nat. 

 size. U. Carboniferous; Staffordshire, ag., angular; d. dentary ; /., 

 frontal; i.d., infradentary ; j., principal gular (jugular); l.j., lateral gular 

 (jugular); m.j., median gular (jugular); mn., mandible; mx., maxilla; 

 op. , operculum ; or., orbit ; p.f., postfrontal ; p.mx., premaxilla ; p.op., pre- 

 operculum ; pa., parietal ; s.o., suborbital ; s.op., suboperoulum ; s.t., supra- 

 temporal ; sq., squamosal; x, x', cheek-plates. (After Traquair.) 



