of the Fishery Boards for Scotland. 123 



nevertheless, sufficiently complete to show that the skull of this species 

 differs distinctly from that of callarias. 



Seen from above the frontal of ogac is a shorter and broader bone 

 than that of callarias. In the latter it tapers much anteriorly. This 

 relation accounts for the broad interorbital measurement on the head 

 of ogac. 



The foramen of the nervus lateralis is covered in callarias by the process 

 of the parietal. In ogac the foramen is above and in front of the 

 process. 



The opisthotics in ogac appear to extend down to the vertical line of 

 the skull : they do not in callarias. 



The vomer seems to be rather more pointed (view from above) in 

 callarias than in ogac. 



The occipital spine in ogac rises high on the frontal, whereas in 

 callarias it is simply a ridge. 



The skull of ogac is, I consider, on the whole shorter than that of 

 callarias. 



Diagnostic Value of other Bones. 



Clavicle. — The clavicle of seglefinus is a characteristically solid bone 

 (fig. 7). The post clavicle of the same species is of a similar build (fig. 

 6). The clavicle and post-clavicle of merlangus are shown in figs. 22 

 and 28. 



The skull and other head bones of aeglefinus are well ossified. 



Otoliths. — The otoliths of the Gadidfe and other fishes have been treated 

 lately by Dr T. Scott. I have therefore included here only five of the 

 species, viz. : — Poutassou (fig. 21), argenteus (fig. 29), saida (fig. 30), ogac 

 (fig. 23, after Vanhoffen), minutus (fig. 56). 



In the case of the three species first discussed in this research, viz., 

 callarias, virens, and pollachius, the comparison between them was carried 

 out on all the bones of the head, and the result was to show that almost 

 every bone had a greater or less specific character. The jaw bones are of 

 much value in this respect. I have not continued this extended com- 

 parison of the skeleton. I publish here, however, drawings of an 

 additional part of the skeleton of pollachius which, so far as I am aware, 

 has not been published. The bones of the head of pollachius -were 

 figured in my paper in the Twentieth Annual Report of the Fishery 

 Board for Scotland, Part III. 



On the Diagnosis of Isolated Bones and Otoliths. 



The presence of certain Gadoids in the stomachs of fishes and other 

 animals has been detected by the otoliths which had resisted disintegra- 

 tion. An example of this is given by Scott, who found a large number 

 of the earstones of merlangus in the stomach of a porpoise. 



Jensen found in the bottom-deposits taken from the Polar Deep 

 between Iceland and Jan Meyan, large numbers of the otoliths of pou- 

 tassou, some of saida, and one each of callarias and virens. 



There are also single bones, the specific identity of which can be 

 recognised at once. For example, several of the bones of seglefinus are 

 of this character, the clavicle and post-temporal being massive in com- 

 parison with those of other species. 



It is, however, an advantage to have several bones of the fish upon 

 which to work out the diagnosis. 



I have on several occasions found on the shore of a small fresh-water 



V-e^Cfc™ 



