of thi Fishery Board for Scotland. 121 



readily reduced to words, and comparison must be made either on the 

 skulls themselves or by means of drawings. 



There is a certain number of characters by which the skulls may be 

 roughly separated into groups. 



Side View. — The first of these is — the shape of the ventral edge of 

 the skull ; that is, formed by the vomer, parasphenoid, and basi-occipital 

 bones. 



If the skull be laid resting on its ventral edge on a flat surface, so that 

 the vomer, from which the teeth have been removed, is directly on the 

 surface, it will be found that the next part of the edge to touch the 

 surface will be : — (a) the basi-occipital, or (&) the hind half of the 

 parasphenoid, or (c) the swollen opistholics projecting below the ventral 

 edge. 



To (a) belong callarias and ogac (fig. 15). 



To (&) belong jEglefinus, (fig. 11), merlangus (fig. 18), virens, 

 pollachius, luscus, minutus, esmarki, poutassou (fig. 24), argenteus 

 (fig. 26). 



To (c) belongs saida (fig. 25). 



The largest number of species, therefore, belong to division (&). In 

 these skulls the basi-occipital is raised above the surface on which the 

 skull rests. The extent to which it rises varies among the species, from 

 the very slight elevation in merlangus to the very high upward bend in 

 argenteus. 



The opisthotics which form the cavities containing the otoliths are 

 very varying in the part they play in the shape of the skull, and the 

 differences may be referred to the following divisions, which are to be 

 noted in a side view of the skull : — 



The opisthotics do not extend down to the ventral edge of the skull in 

 callarias, virens, pollachius. 



They extend down closely to the ventral edge — teglefinus. 



They extend down to the ventral edge of the skull — aeglefinus, 

 merlangus, luscus, esmarki, poutassou, [ogac ?]. 



They extend downwards beyond the parasphenoid ; they project 

 ventrally, in saida, argenteus. 



A marked difi"erence is found in the shape of the inter-orbital arch, the 

 base of which is furnished by the parasphenoid, while its rim is formed 

 by the pre-frontal, frontal, orbito-sphenoid, and pro-otic. 



The arch is less than a semi-circle, i.e., the length of its base is more 

 than twice its height, in callarias, ogac, virens, pollachius, merlangus, 

 saida, poutassou. 



The arch is nearly a semi-circle in seglefinus and luscus. 



The arch is a semi-circle in esmarki, minutus, argenteus. 



The ethmoid slopes backwards much in virens, pollachius, saida, 

 poutassou, argenteus, esmarki. 



The anterior edge of the ethmoid is nearly vertical in callarias, ogac, 

 seglefinus, merlangus, luscus, minutus. 



There is a prominent notch in the front edge of the ethmoid in luscus, 

 minutus, esmarki, argenteus. 



A small notch is sometimes made out, but is sometimes absent — 



Uarias, ogac, virens, pollachius. 



The notch is absent — saida, poutassou. 



The occipital spine rises high on the frontal bone in ogac, virens, 



llachius, merlangus, minutus, esmarki, argenteus, seglefinus, and luscus. 



is very high in the two last named. 



The occipital spine does not rise off the frontal bone, but begins as a 



