356 THE FKKSII-WATKI! FISIIKS (F KTKOPE. 



wide ; the number of branchiostegal rays, according 1 to Giinther, is seven to 

 eight. Heckel and Kner state that the number of branchiostegal rays is some- 

 times ten on each side, sometimes nine on the right and ten on the left, though 

 a St. Petersburg example shows eleven on the left and ten on the right, an 

 unsymmetrical arrangement very common in the genus. The gill-rakers are 

 pointed, and compressed at the base. Those of the last branchial arch are 

 nine or ten in number, short, conically pointed, and not denticulated. The 

 opercular shield is remarkable for the small size of the operculum, and the 

 broad sub-opercul um, which is placed high up. 



The dorsal fin commences in the second third of the length, with a short 

 ray. The rays increase in length to the first jointed ray, but the height of the 

 fin differs with age, and it is only in the fourth to the fifth year that the fin 

 acquires its full development, and then when laid back it touches the adipose 

 fin with its last ray. The adipose fin, which is common to all the Salmon 

 tribe, is highly suggestive, as probably a consequence of fatty degeneration, in 

 which case it may perhaps represent a second fin of jointed rays which has 

 entirely disappeared in these fishes, but may have existed in some ancestral 

 type ; nevertheless, that there is no necessary connection between a fatty fin 

 and a bony skeleton to support it is shown by the development of a fatty fin 

 on, the backs of Dolphins and other cetacea. The anal fin is opposite to the 

 adipose fin ; it has commonly four unjointed and eleven jointed rays ; it is the 

 shortest of all the fins, and strongly truncated behind. The ventral fins are 

 opposite the middle of the dorsal ; they are broader than the pectoral, but 

 rather shorter. The caudal fin is as long as the head ; its forking is very 

 variable, and it is evenly-lobed. 



The lateral line descends at the back of the head, and then runs straight 

 to the tail a little above the middle of the body; it opens with simple pores 

 in a smaller row of scales than those on each side of it. The mucus-canals of 

 the head are similar to those in Coregonus. They are well marked in the sub- 

 orbital bone, open with a row of pores over the eye, and there are three or four 

 pores on each branch of the lower jaw. The scales are adherent, larger than 

 in the Salmon. They have fine concentric striping, are generally convex at the 

 free margin, with a few short delicate rays. The posterior border is notched 

 and truncate, so that the scale is much higher than long. The scales are 

 smaller on the back than on the sides, but smallest on the abdomen and throat ; 

 they become gradually larger round the ventral fin. 



The scales on the sides commonly have the aspect of being arranged in 

 parallel lines, and the name Grayling has sometimes been supposed to be a 

 corruption of et grey lines," due to this appearance. The head and fins are free 

 from scales, but the caudal is covered at its longest ray for half its length 



