124 



BATRACHIA. 



p. 77). Moreover, the bones of the cranial roof never re- 

 semble those of the known Dipnoi, but are always normal 

 as in the Crossopterygians ; while they form a continuous 

 shield with the robust cheek-plates and the transverse chain 

 of supratemporal elements. The accompanying diagram of the 

 cranial roof-bones of Pelosaurus (fig. 81 B) shows the ordinary 

 arrangement of these elements, which is subject only to minor 

 variations and may be instructively compared with the skull of 



A. 



Fm. 81. 



Diagrammatic outline of Cranial Eoof and outwardly crushed Cheek-plates of 

 Rhizodopsis (A) compared with the corresponding bones of a Stegocephalian, 

 Pelosaurus (B). /., frontal ; ju., posterior suborbital (A) or jugal (B) ; 

 Z, anterior suborbital (A) or lachrymal (B) ; mx., maxilla ; n, nasa ; pa., 

 parietal; prf,, prefrontal ; ptf., postfrontal; pto., upper posterior sub- 

 orbital (A) or postorbital (B) ; q.j., cheek-plate resembling quadrato-jugal of 

 Stegocephalia ; s.t., supratemporals and cheek-plate (prosquamosal) ; 

 sq., squamosal. (Fig. B after Credner.) 



Rhizodopsis (fig. 57, p. 75), which is diagrammatically repre- 

 sented with the cheeks crushed outwards and the bones re- 

 lettered in fig. 81 A. The parietals (pa.), frontals (/), squa- 

 mosals (sq.), and postfrontals (ptf.), occupy their usual position ; 

 and there are also pre frontals (prf.) and nasals (n). The 

 pineal foramen always occurs in the parietal, and not in the 

 frontal region. The cheek-plates are much reduced in number, 

 there being occasionally one in front of the eye (" lachrymal," I), 

 always one below the eye ("jugal," ju.), and another behind 

 (" postorbital," pto.) ; while the largest and hindermost plate 

 of the cheek, commonly named supratemporal (s.t.), seems to 



