248 Part III. — Twentieth Annual Re^jort 



By means of the characters which were selected, similarities and more or 

 less prominent differences between the three species have been brought out. 

 But since in a large number of these cases the differences are of small 

 amount, and require therefore rather minute measurement, they are not 

 of much value in a specific description. The specific description should 

 contain nothing more than a sufficiency of characters to ensure the dis- 

 crimination of the form. These should, moreover, be obvious and readily 

 marked characters. In certain works the specific descriptions are ex- 

 tremely cumbersome, and so overloaded with detail that it is a matter 

 of some difficulty to diagnose the species of a fish by their aid. 



For the characters of the Family Gadid^, and of the Genus Gadus, we 

 may adopt the description given in Smitt's "Scandinavian Fishes," 

 Stockholm, 1893, Part I., viz :— 



Fam. Gadid^. 



Body elongated, comioressed, clavate or fusiform, and covered with 

 tJmi cycloid scales. Caudal fin distinct from the other vertical fins. Jaws 

 furnished with teeth. Gill-openings large ; hranchiostegal membranes 

 more or less completely free from the isthmus. Pseudohranchue wanting, 

 or glandular. Air-bladder and pyloric appendages generally tuell- 

 developed. 



Genus Gadus. 



Three dorsal fins, all fully developed, and two anal fins. Peduncle 

 (finless part) of the fail distinctly marTied of. Ventral fins normal, 

 with 6 rays. Jaw-teeth and vomerine teeth present. BrancMostegal 

 rays 7. 



Specific Description. 



It is not my purpose to give a complete specific description of the three 

 species, since they alone of the members of the genus Gadus are under 

 consideration. A few characters by which they may be readily separated 

 will be given below. 



Barbel. — In most systematic works it is stated that the lythe has no 

 barbel. That is true so far as it refers to an external barbel. Beneath 

 the skin, however, the cartilaginous basis of the barbel may be found on 

 dissection. {Vide b. Fig. 29, PL I.) The saithe has a very small barbel ; 

 that of t)ie cod is large and prominent. 



Saithe (Gadus virens). — Parnell, in his "Fishes of the Firth of 

 Forth," divided the saithe into two species, in one of which, Merlangus 

 carbonarius, the mandible projected in front of the premaxilla, while in 

 the other, Merlangus virens, the upper and lower jaws were of equal 

 length. The form which he described as of the latter species measured 

 10 inches (25 cm.), and was no doubt a young saithe. In the young 

 saithe the upper and lower jaws are of about the same length, while in 

 the adult saithe the lower jaw projects in front of the upper. 



The scheme given below includes certain readily gauged characters, 

 sufficient in number and importance to enable the three species to be 

 easily separated : — 



[Table. 



