304 



PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Feb. 21, 



[=heiglit?], and is at right angles to the direction of the lateral 

 line of the fish." 



Figs. 1-4. — Diagrammatic restorations of the heads of (1.) Amphicen- 

 trum, (2.) Platysomus, (3.) ^chmodus, and (4.) Pycnodus 

 {after ThioUihre), 



Fiff. 1, 



Fig. 3. 



1^1^ 



s.o. 



Fig. 2. 



Fig. 4, 



Pa., 



P.Pr... 



A. Fr.--":: 



:■.:::;.:;/ 



Eth. 



""'/^^B 



Na. -.. ,. 



-".^^r^ 



Pmx. 



/%L -> 





^i.ijtiiii-' ^ 





Mn. 





Br..'' 



.,-• Op. 



S.Op. 



Eth. 



^-« Sph. 



Figure 2 is a diagrammatic restoration of the stmcture of the 

 head of Platysomus. The occipital crest rises from a narrow bone 

 (S.O.), lodged between the square parietals (Pa.), and connected in 

 front with the frontals (Fr.), which, broader behind, narrows in 

 front, receiving in its outer excavated margin two bones, which com- 

 plete the orbital circle superiorly. The posterior of these (P.Fr.) 

 extends to the parietals and thus represents a united postfrontal 

 and squamosal (mastoid, Cuv.). The anterior frontal (A. Fr.) dips 

 down, and gives insertion to the narrow suborbital chain which is 

 attached behind to the P, Fr. The anterior frontals of opposite sides 



