276 P(trt III. — Tvjentieth Annual Report 



posterior surface of the second ceratobranchial. The sides of the groove 

 in the hypobranchial are prominent. The outer wall of this furrow is in 

 the lythe not nuich higher than the inner wall ; in the saithe the 

 outer is much higher, and attains its greatest height at the angle of the 

 bone. In the lythe the outer wall is lowest at that point. While in 

 the saithe and lythe this wall ends just a little in front of the angle, in 

 the cod it is carried forward to the anterior extremity of the bone. In 

 the saithe and lythe the groove passes from the ventral to the external 

 surface of the bone at its angle, whereas in the cod the groove is wholly 

 on the ventral surface. 



In the cod the third hypobranchial, though retaining the trowel- or 

 scoop-shape shown hj those bones in the saithe and lythe, is much flatter. 

 In the lythe the bone has a distinct slender handle, which is not so 

 apparent in the saithe and cod, where the handle is united in its whole 

 extent to the outer edge of the blade by a thin bone plate. When the 

 bone is in situ it is seen that in the saithe and lythe the outer edges of the 

 blade and of the handle are in one and the same straight line, whereas in 

 the cod the outer edge is curved. The handle in the cod turns in sharply 

 towards the middle line : in the saithe and lythe this occurs in a hardly 

 noticeable degree. 



Geratohranchials (cer. Br.). 



Cod, Fig. 22, PI. XI. : Saithe, Fig. 16, PI. XI. : Lythe, Fig. 21, PI. IV. 



In the case of the ceratobranchials, as in all the other branchial bones, 

 those of the cod are nnich thicker and broader thati those of the saithe, 

 which in their turn are a little heavier than those of the lythe. 



The first ceratobranchial of the saithe and lythe has a rather deep 

 longitudinal furrow on the anterior surface ; this is not found in the cod. 

 In the saithe the posterior surface of the bone is crenate at the angle of 

 the bend ; in the lythe and cod it is smooth. 



Except in their different thicknesses no satisfactory points of difference 

 were made out between the second and third ceratobranchials of the 

 three species. Moreover the differences used to separate the second and 

 third ceratobranchials of the lythe were not found of so much value in 

 connection with the saithe and cod. In both the saithe and the lythe the 

 third ceratobranchial is a deeper bone than the second. 



In the fourth ceratobranchial the differences between the three species 

 were very slight. 



Epihrancliicds (ep. Br.). 

 Cod, Fig. 23, PI. XI : Saithe, Fig. 17, PI. XL : Lythe, Fig 21, PI. IV. 



The triangular process on the hind surface of the first epibranchial is 

 rather smaller in the saithe than in the lythe, and while in the latter the 

 apex of the process is rounded, in the former it is a blunt angle. In the 

 cod the process is low and not triangular in shape. 



In the third epibranchial of the saithe the toothed area is very small, 

 and much less than that in the cod and lythe. The tooth-sockets in this 

 bone are larger in the cod than in the other two. In the saithe also the 

 toothed area is at its superior corner raised up from the side of the upper 

 articular process. 



No very easily described differences were noticed in respect to the 

 second and fourth epibranchials. 



