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 (Oxcorhynchus 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 
“ Tlypsifario Kennerlyt.” This species appears to 
be sometimes landlocked in mountain lakes, in 
