1926] Snyder: The Trout of the Sierra San Pedro Martir 421 



coastal region of California and Oregon. It occupies exactly the same 

 relation to the rainbow trout as does the San Pedro bluebird to the 

 western bluebird and other forms to the northward: it is a boreal 

 form stranded in a low latitude. It reached its present habitat when, 

 because of favorable climatic conditions, the range of the trout, in 

 common with many other northern species, extended farther south. 

 Even with the present general temperature, if the precipitation along 

 the west coast were sufficiently increased, the rainbow trout, because 

 of its ability to migrate through salt water, would experience little 

 difficulty in entering many of the southern coastal streams and 

 establishing itself in them. 



Because of its isolation, Salmo nelsoni may conveniently be regarded 

 as a distinct geographic race ; but in attempting to distinguish indi- 

 viduals from those of the rainbow trout, S. irideus, by anatomical 

 characters, including color and form, many difficulties arise. 



The appearance of an error in the enumeration of the scales of 

 the lateral series, "38-170-26" (and, strange to say, the same mistake 

 was made in the illustration) made it difficult for the original author 

 (Evermann, Barton Warren, Proc. Biol. Soc. Wash., 21, 1908, p. 19) 

 to determine the relationships of the species. He concluded, however, 

 that it is most closely related to the Kern River trout and the various 

 species of golden trout of the Kern River region, agreeing with them 

 in the small scales, the position of the dorsal, and the bright tips of 

 the dorsal, anal, and ventral fins. 



As a matter of fact the scales do not differ in size, as expressed by 

 a count of the lateral series, nor is there anything distinctive in the 

 position of any of the fins, as is shown in the accompanying table (1) 

 where measurements of several examples of S. nelsoni and S. irideus 

 are given. The length of the body is here measured from the tip of 

 the snout to the base of the caudal fin and recorded in millimeters. 

 The other measurements are expressed in hundredths of the length. 



Mr. Barton A. Bean, Curator of Fishes in the United States 

 National Museum, has examined three paratypes of S. nelsoni which 

 are in that collection, with this result : scales in the lateral series, 128, 

 127, 139. 



It will be seen that the lateral series of scales number from 127 to 

 143 in Salmo nelsoni, and about the same in S. irideus. An examina- 

 tion of a large series of the latter seems to point to an extreme varia- 

 tion of from 110 to 150 lateral scales, the numbers near either end 

 of the series occurring only rarely. 



