96. FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. V. 



North America, one Salmo salar Linnaeus is anadromous, while the 

 other two, Salmo scbago Girard and Salmo ouananiche McCarthy, are 

 land-locked ; those in the Rocky Mountains and western streams with 

 few exceptions remain in fresh water, the exceptions comprise a few 

 species which usually inhabit the streams near the sea, and which 

 spend a portion of their time in salt water. All of the species are 

 very variable and difficult to distinguish. ' The almost infinite varia- 

 tions of these fishes are dependent on age, sex, sexual development, 

 food, and the properties of the water." The young are barred. 

 The size of these fishes seems to depend largely on the extent of 

 water and the abundance of food. The water also has a marked 

 influence on colors. Trout found in shaded streams with clear rapid 

 water are brightly colored, and profusely spotted with black; those 

 which spend considerable time in brackish or salt water are silvery 

 and with few or no spots. 



89. Salmo irideus Gibbons. RAINBOW TROUT. 



Salmo irideus Gibbons, Proc. Cal. Acad. Sci., 1855, 36; San Leandro 

 Creek, Alameda Co., California: Jordan & Evermann, Bull. 

 47, U. S. Nat. Mus., 1896, 500. 



Headwaters of Pacific coast streams of Durango north to Wash- 

 ington. 



Head 4; depth 3^3 ; D. 10; A. 9; scales 135. Body rather robust; 

 head moderate; mouth large; maxillary reaching posterior margin of 

 eye, its length 2% in head; diameter of eye 3?; length of mandible 

 if; origin of dorsal fin .slightly nearer tip of snout than base of 

 caudal ; length of pectoral i ^ in head ; ventral i ? ; least depth of 

 caudal peduncle 2^ in head; branchiostegals 10. 



Color olive brown, darker above; sides with a few scattered dark 

 blotches; a few small black spots on upper and posterior part of 

 caudal peduncle; dorsal fin with black spots, none on other fins; basal 

 YT, of anal dark; ventrals with a dark shade; specimens 3 inches in 

 length with 9 or 10 pale marks on the side, the dorsal fin black spotted, 

 but no spots on other fins. 



Four specimens collected June, 1902, by Mr. E. Heller at San 

 Antonio, Lower California, the longest specimen 5 .80 inches in length. 

 This species reaches a weight from ]/?. (in small mountain brooks) to 

 6 pounds. 



There is a species of trout found in the streams on the Pacific 

 slope of the Sierra Madre Mountains in Chihuahua and Durango. I 

 have not seen any specimens of this trout and so, provisionally at 

 least, regard it as this species. Mr. John Ramsey, General Manager of 

 the R.-G., S.-M. & P. R. R., informs me that a trout is quite abundant 



