of the Fishery Board for Scotland. 261 



just about four-lifths of the greatest length {i.e., the upper surface) ; in 

 the cod it is equal to the length, and in the saithe the base is only equal 

 to half the length. 



Atlas Vertebra (At.). 

 Cod, Fig. 28, PI. XI. : Saithe, Fig. 27, PL XI. : Lythe, Fig. 26, PL XI. 



The atlas vertebra is firmly attached to the skull. It articulates with 

 the basisphenoid, and is bound by ligament to the exoccipital, while its 

 neural spine is firmly connected by ligaments to the occipital spine. 



The differences between the atlas vertebrje of the three species are not 

 striking. In the saithe the neural spine is thin, while in the cod and 

 lythe the spine is much thicker. 



Dentary (D.). 

 Cod, Fig. 42, PL X. : Saithe, Fig. 18, PL X. : Lythe, Fig. 12, PL IV. 



As would be expected from the outward form of the jaws, the mandible 

 of the lythe is longer than those of the cod and saithe, while in general 

 the arch formed by the united mandibles of the lythe resembles that of 

 the saithe and differs from that of the cod. The united dentaries form 

 an arch which in the saithe and lythe is narrow at its apex : in the cod it 

 is broadly rounded. The hind extremities of the dentaries turn inwards 

 in a horse-shoe form in the cod, whereas in the saithe and lythe they are 

 directed backwards and outwards (Cod, Fig. 31 : Saithe, Fig. 29: Lythe, 

 Fig. 30, PL XL). Then the ventral descending plate of the dentary 

 curves inwards towards its fellow on the opposite side in the cod and 

 lythe, but does not do so in tiie saithe. In the shape of the apex of 

 the arch considerable diflference is noted between the three species. 

 The tuberosities on the anterior ends of the dentaries project in the 

 saithe well in front on either side of the symphysis : in the lythe they 

 are very small, and in the cod even less conspicuous. In neither of the 

 two latter do they project beyond the gently curved contour of the apex 

 of the arch. 



The dentaries are, moreover, to be readily distinguished by the size of 

 the teeth, or, if they are absent, by the diameters of the tooth-sockets. 

 In the saithe there is a more or less complete double row of small teeth on 

 each mandible ; at its anterior end, and close to the symphysis, there is 

 an increase in the breadth of the toothed area, three rows being usually 

 very distinct. In the lythe there is usually one complete row on each 

 dentary, with a doubling of the row, by the addition of smaller teeth, at 

 the side of the symphysis. The teeth of the main row in the lythe are 

 much larger than those of the saithe, and even the small tooth-sockets of 

 the lythe are as big as the largest in a similarly-sized dentary of the 

 saithe. In the cod there are two rows, an outer of smaller teeth and a 

 hind row of teeth which when compared to those of the saithe and lythe 

 are huge. 



When the united dentaries are viewed from in front, the apex is seen 

 to be slender, in dorso-ventral measurement, in the cod, while in the 

 saithe and lythe it is massive. Inferiorly, the ends of the dentaries 

 recede from one another at the symphysis, the saithe leaving a wide 

 angle, whereas in the lythe there is only a very slight separating notch. 



In side view (from without) the different breadths of the descending 



