28 



MR. E, LEONARD GILL ON THE PERMIAN 



external angle of the post-temporal. From thence it crosses the 

 supraclavicle obliquely to the first scale of the lateral line series. 

 The under surface of the frontal is marked by a conspicuous 

 ridge on either side parallel to the curved orbital margin. It 

 underlies the line of sensory pits and maybe connected with their 

 canal, or it may only be a boundary wall for the chondrocranium 



Text-figure 7. 



J.cp 



op. 



s.d. 



cop 



mx. 



pmx 



Acentropliorus varians. Head crushed obliqueh' from the left side and from below, 

 showing branchiostegal ra3^s and parts of shoulder-girdle ; Kirkby Collection, 

 Hancock Museum. About four times natural size, asp., alisphenoid ; c.hy., 

 right ceratohyal ; cor., circumorbitals ; fr., frontal, left side from below ; 

 7i.7jy., right hypohyal ; i.oj?., interoperculum ; Z.6r.,left branchiostegals; l.cl., 

 part of left cleithrum J L^., left lower jaw; mx., maxilla; op., operculum; 

 pal., bones of palate ; • p.mx., premaxilla ; p.op., preoperculum ; r., ribs ; 

 r.br., right branchiostegals ; r.cl., point of right cleithrum; r.J., right 

 lower jaw ; so., small scales of jugular region ; s.cJ., supraclavicle, displaced; 

 s.op., suboperculum. 



in this region. As in Amia, one of the pits on the squamosal 

 forms a notch in the margin of the bone at the point whei-e the 

 main canal was joined by the branch ti^a versing the preoperculum. 

 The supratemporals are strongly grooved and pitted by the 

 transverse branch of the canal. The situation of all these pits 



