of the Fishery Board for Scotland. 259 



inside with the parietal and paroccipital. Eetween the postfrontal and 

 the squamosal there is a large depression filled with cartilage ; this forms 

 the anterior part of the hyomandibular aocket. The upper rim of the 

 socket in the squamosal stands well up from the surface of that bone in 

 the saithe and lythe, whereas in the cod the rim is low and sometimes 

 absent. The bone-fold on the upper surface of the squamosal which 

 shields part of the infraorbital canal, ends posteriorly, in the cod and 

 lythe, just about the level of the hind margin of the hyomandibular 

 socket, whereas in the saithe it comes well behind that point. The 

 extreme breadth of the bone-fold is in the lythe greater than in the 

 saithe. In the cod the end of the corresponding bone-fold of the frontal 

 overlaps for a bit the anterior extremity of the fold of the squamosal ; in 

 the saithe and lythe they meet, and simply the extreme edge overlaps. 



The articulation of the squamosal with the paroccipital is a cartilaginous 

 union. In the cod these two bones are, in the region of the union between 

 them, semi-cartilaginous. 



Orhitosphenovl (Or. S.). 



Cod, Fig. 43, PI. IX. : Saithe, Fig. 7, PI. IX. : Lythe, Fig. 22, PI. IX. 



The orbitosphenoid is a little semicircular bone inserted between the 

 frontal, postfrontal, and prootic. It is seen only in side and ventral views 

 of the skull. The two orbitosphenoids are connected together by a carti- 

 lage which is closely applied to the lower surface of the frontal. 



Prootic (pr 0.). 

 Cod, Fig. 47, PI. IX.: Saithe, Fig. 12, PI. IX.: Lythe, Fig. 26, PI. IX. 



The prootic articulates with the postfrontal and orbitosphenoid in front, 

 with the squamosal above, the parasphenoid below, and the opisthotic 

 behind. The edge of the prootic overlaps the orbitosphenoid, and it itself 

 is overlapped by the squamosal, parasphenoid, and opisthotic. The 

 prootic shares superiorly in the formation of the cartilage-filled depression 

 in the front part of the hyomandibular socket. 



The internal surfaces of these bones in the saithe and lytlie resemble 

 one another more than they do that of the cod. On the anterior upper 

 part of this surface there is a fan-shaped bony mass. In the cod it is 

 distinctly fan-shaped, but in the lythe and saithe it has a deeply incurved 

 posterior edge. Below there is a smooth curved articular border in the 

 saithe and lythe, whereas in the cod it is irregular and laminate. 



Parietal (P.). 

 Cod, Fig. 38, PI. IX. : Saithe, Fig. 3, PI. IX. : Lythb, Fig. 18, PI. IX. 



The parietal articulates in front with the frontal, on its inner side with 

 the supraoccipital, on its outer side with the postfrontal and squamosal, 

 and behind with the paroccipital. 



There is a distinct difference in the shape of this bone between the 

 saithe and the lythe. In the lythe its breadth is equal to about two- 

 thirds of its length, whereas in the saithe it is less than one-half. In the 

 cod it is about one-half. 



Posteriorly the bone has in the saithe and lythe a long thick sutural 



