Salmonide 317 
among the salmon proper only two species, Salmo salar and 
Salmo trutta. The latter species, the sea-trout or salmon-trout 
of England and the estuaries of northern Europe, is similar to 
the salmon in many respects, but has rather smaller scales, 
there being fourteen in an oblique series between the adipose 
fin and the lateral line. It is not so strong a fish as the salmon, 
nor does it reach so large a size. Although naturally anadro- 
mous, like the true salmon, landlocked forms of the salmon- 
trout are not uncommon. These have been usually regarded 
as different species, while aberrant or intermediate individuals 
are usually regarded as hybrids. The salmon-trout of Europe 
have many analogies with the steelhead of the Pacific. 
The present writer has examined many thousands of Ameri- 
can Salmonide, both of Oncorhynchus and Salmo. While many 
variations have come to his attention, and he has been com- 
pelled more than once to modify his views as to specific dis- 
tinctions, he has never yet seen an individual which he had 
the slightest reason to regard as a “hybrid.” It is certainly 
illogical to conclude that every specimen which does not corre- 
spond to our closet-formed definition of its species must therefore 
be a “hybrid”’ with some other. There is no evidence worth 
mentioning, known to me, of extensive hybridization in a state 
of nature in any group of fishes. This matter is much in need 
of further study; for what is true of the species in one region, 
in this regard, may not be true of others. Dr. Gunther observes: 
‘Johnson, a correspondent of Willughby, had already ex- 
pressed his belief that the different salmonoids interbreed; 
and this view has since been shared by many who have ob- 
served these fishes in nature. Hybrids between the sewin 
(Salmo trutta cambricus) and the river-trout (Salmo fario) were 
numerous in the Rhymney and other rivers of South Wales 
before salmonoids were almost exterminated by the pollutions 
allowed to pass into these streams, and so variable in their 
characters that the passage from one species to the other could 
be demonstrated in an almost unbroken series, which might 
induce some naturalists to regard both species as identical. 
Abundant evidence of a similar character has accumulated, 
showing the frequent occurrence of hybrids between Salmo 
fario and S. trutta. . . . In some rivers the conditions appear 
