192 American Fisheries Society 



marine forms from their southern to their northern limit. 

 Owing, doubtless, to modifications of the environmental condi- 

 tions of the coastal forms other than those directly pertaining 

 to the glacial retreat, such as warm oceanic currents for 

 instance, the marine trout would be able to move farther 

 north than they otherwise would. 



So while there is demonstrable evidence of the zone system 

 in the interior, it is not so plainly evident along the coast. 

 Consequently among them there appears to be a medley of 

 forms in some localities, which may be due to predominantly 

 fresh water forms sometimes mingling with predominantly 

 marine forms. Or it may possibly be partly attributable to 

 hasty examination, to attention being directed to the wrong 

 structures or characters. The usual characters emphasized in 

 descriptions are often those which are^never diagnostic, or they 

 may be structures or dimensions which vary with the size, age, 

 sex, and breeding condition. 



As concerns the steelhead-rainbow question, it is probably 

 true that the marine forms from one end of the habitat zone 

 to the other, taxonomically at least, must be regarded as the 

 same species. Many of the trout occurring in waters acces- 

 sible to this species are regarded locally, at least, as rainbow 

 trout and the anadromous forms as steelhead. Occasionally 

 some other species may make its way into salt water and when 

 reascending the stream, perhaps with the common steelhead, 

 it is called steelhead. 



Now the fact appears to be that the form bearing the name 

 Salmo irideus is an anadromous form. But the form from the 

 McCloud River which has been propagated artificially under the 

 name of "rainbow trout (Salmo irideus)" is a distinct species 

 which Jordan has named Salmo shasta. Some time ago Jordan 

 stated that the name rividaris, formerly regarded as a synonym 

 of irideus, should be used as the designation of the steelhead, 

 on the ground that Richardson had applied the name to a 

 young blueback salmon (Oncorhynchus nerka). The blueback 



