660 



premaxillaries, nasals, frontals, parietals, prefrontals and postfron tals 

 in the Crossopterygii and Stegocephali. But it is not so easy with 

 the squamosal region and the elements behind the parietals. All the 

 Crossopterygians possess opercular bones and the question of course 

 at once arises, as to the fate of these elements in the Stegocephali? 

 The solution of this important question seems to be possible by the 

 study of the lateral line system of the skull ^). W^ shall first examine 

 the conditions in Amia (Fig. 1), which are known to us by the splendid 



workofÄLLis. We can distinguich 

 4 canals: 1) The infraorbital 

 canal, which is the direct con- 

 tinuation of the lateral line of the 

 body, traverses the posttempo- 

 rals, Parker, Gill 1871 (supra- 

 scapulare, Cuvier, Owen, Sage- 

 mehl, Allis), supratemporal. 

 Barker, Cuvier, Agassiz, Owen 

 (extrascapularia, Stannius, Sage- 

 mehl, Allis), squamosal, postfron- 

 tal, post- and suborbitals, lacrimal, 

 antorbital and ethmoid, joining in 

 this element the canal of the other 

 side; 2) the supraorbital canal 

 passing through nasal, frontal, 



Fig. 1. Amia calva, L. (Prom Allis.) 



n nasal. / frontal, p parietal, sq squamosal, ^»'o praeoperculum. stp supratempo- 

 ralia. ptp post-temporal, spcl supraclavicle. 



1) Already Pollabd attempted to use the canals of the lateral-line-system, 

 to homologize the elements of the skull of Polypterus with the Stegocephali ; 

 but not being acquainted with the supratemporal cross-commissure in the 

 Stegocephali and erroneously describing a portion of the suborbital canal 

 in Metopias as the operoulo-mandibular canal, his homologies are all at 

 fault, with the exception of the median pair of the suprateraporale of 

 Polypterus with the supraoccipital plates of the Stegocephali. 

 Pollaed's homologies are the following: 



Polypterus Stegocephali 



supratemporal = supraoccipital (supraoccipital plate), 

 posttemporal = epiotic (paroccipital plate), 



operculum = supratemporal (prosquamosum), 

 suboperculum = quadratojugal, 

 praeoperculum = jugal. 



