GREGORY, PRESEXT STATUS OF ORIGJX OF TETRAPODA 335 



KHIPIDISTIA STEGOCEPIIALI 



A. Dorsal series 

 1. Rostro-frontal segment 



Premaxillse \ Premaxillse ~\ 



Ethmoid C More or less undivided Ethmoid C Sharply separated 



Nasals ) Nasals ) 



"Anterior frontals" (ectethmoid) ? Septomaxillary 



Frontals Frontals 



2. Parietal segment 



Parietals Parietals 



"Squamosals" (pterotics) Pterotics ("Supratemporals", "supra- 



squamosals") 



3. Occipito-nuchal segment 



(Nuchal median "supratemporal" ) Paired dermo-supraoceipitals (post- 



parietals) 

 Lateral "supratemporals" Tabularia ("epiotics") 



B. Circumorbital series 



Including a variable number of ele- Including always five elements : pre- 

 ments : in Holoptychiidse, Glyptopo- frontal lacrymal. jugal, postorbital. 



midse, three ("prefrontals", "post- postfrontal 



frontals", "suborbitals'^) ; in Osteo- 

 lepidse four or five ; in Rhizodontida? 

 five 



C. Temporal-opercular series 



Pterotic ("squamosal") Pterotic (supratemporal. suprasqua- 



mosal) 

 Cheek plate X ( — posterior postor- Squamosal 



bital of Amia) and true operculum 

 Cheek plate X' ( interoperculum ) Quadratojugal 



Operculum ? Become membranous, or transformed 



into tympanic membrane of Stere- 



ospondyli 

 Suboperculum ? Lost (become membranous) 



The dorsal segments as al)ove defined include only transverse zones ; 

 but, running longitndinall}^ from the top of the orbit to the top of the 

 occiput and external to the primitive spiracular cleft (PoJ}/pferu><. Jfolo- 

 ptychius), there is a postorbito-pterotic row which corresponds in posi- 

 tion to the postorbitals, intertemporals and pterotics (supratemporals) 

 of Stegocephali. 



