48 SCIENCE SKETCHES. 



has an average weight of 22 pounds, but individ- 

 uals weighing 70 to 100 pounds are occasionally 

 taken. It has about 16 anal rays, 15 to 19 branchi- 

 ostegals, 23 (9+14) gill-rakers on the anterior 

 gill arch, and 140 to 185 pyloric cceca. The scales 

 are comparatively large, there being from 130 to 

 155 in a longitudinal series. In the spring the 

 body is silvery, the back, dorsal fin, and caudal fin 

 having more or less of round black spots, and the 

 sides of the head having a peculiar tin-colored 

 metallic lustre. In the fall the color is often black 

 or dirty-red, and the species can then only be 

 distinguished from the dog-salmon by its technical 

 characters. 



The Blue-back Salmon (Oncorhynchus nerka) 

 usually weighs from 5 to 8 pounds. It has about 

 14 developed anal rays, 14 branchiostegals, and 

 75 to 95 pyloric cceca. The gill-rakers are more 

 numerous than in any other salmon, the number 

 being usually about 39 (16 + 23). The scales are 

 larger, there being 130 to 140 in the lateral line. 

 In the spring the form is plumply rounded, and 

 the color is a clear bright blue above, silvery be- 

 low, and everywhere immaculate. Young fishes 

 often show a few round black spots, which disappear 

 when they enter the sea. Fall specimens in the 

 lakes are bright red in color, hook-nosed and slab- 

 sided, and bear little resemblance to the spring 

 run. Young spawning male grilse are also pecu- 

 liar in appearance, and were for a time considered 

 as forming a distinct genus, under the name of 

 " Hypsifario Kennerlyi" This species appears to 

 be sometimes landlocked in mountain lakes, in 



