256 Part III. — Twentieth Annual Report 



crests of the saithe and lythe are very prominent, while their little flat 

 representatives in the cod are not by any means conspicuous. 



The long posterior free end of the squamosal unites with a process of 

 the opisthotic. In the saithe this latter process does not extend back- 

 wards to the tip of the squamosal ; it stops some distance short of it. In 

 the lythe and cod the process of the opisthotic extends to the end of the 

 squamosal, and together they form a broad expanded end to the double 

 process. In the saithe the process of the squamosal projects backwards 

 well beyond the hind edge of the supraoccipital ; in the lythe it just 

 reaches that level, and in the cod a little beyond that point. 



The side of the bony canal on the front part of the frontal is seen in 

 side view to be much higher in the saithe and lythe than in the cod. 



One important difference between the skulls of the saithe and lythe on 

 the one side and the cod on the other is in the shape of the parasphenoid. 

 When the skull is looked at from the side it is seen that the ventral edge 

 of this bone is in the cod practically straight, while it is distinctly 

 curved in the saithe and lythe. Thus if the skull of the cod is placed 

 resting on its vomer and basioccipital, the whole of the parasphenoid is 

 quite above the table. But in the case of the saithe and lythe, the skull 

 would rest on the vomer and the parasphenoid, while the basioccipital 

 would be raised up clear of the supporting plane, the part of the 

 parasphenoid which is directed inferiorly most is that part just below the 

 prootic. This condition is shown in Plate VII., though in the case of the 

 skull of the saithe the beud in the parasphenoid is usually greater than 

 in the case there reproduced. 



In a side view of the skulls slightly from above it is seen that the 

 posterior vertical edge of the paroccipital, which with part of the upper 

 posterior edge of the opisthotic and the upper outer edge of the 

 exoccipital forms the outer posterior edge of the part of the cranium con- 

 taining the auditory organ, is almost vertical in the cod, having a slight 

 forward slope, and in the saithe slopes well forward. In the lythe there 

 is an intermediate condition between these two. 



Hind View. 

 Cod, Fig. 41, PI. VII. : Saithe, Fig. 42, PI. VII. : Lythe, Fig. 43, PI. VII. 



The hind lateral expansions of the supraoccipital overhang the exocci- 

 pitals, thus forming depressions in the hind wall of the cranium in which 

 are lodged the anterior dorsal trunk muscles. In the lythe the depres- 

 sion is shallower than in the cod, and in the cod shallower than in the 

 saithe. 



The cranium is more broadly rounded below in the lythe and cod than 

 in the saithe. 



In the hind view the parietal crests of the saithe and lythe are seen 

 projecting above the paroccipitals, but they are hidden in the cod. 



Disarticulated Skull. 



Vomer (V,), 



Cod, Fig. 30, PI. IX.: Saithe, Fig. 11, PI. IX.: Lythe, Fig. 29, PI. IX. 



There is little difference, in addition to that of size of the teeth, to be 

 noted between the vomers of the three forms. This bone is in the cod 

 much heavier and more massive than that in the saithe and lythe. 



