4 Henshaw on the Species of the Genus Passer ella. 
more than one having strongly hinted at the probable specific iden- 
tity of the four, while the methods in which they have been com- 
bined have been nearly as various as the number of authors who 
have had occasion to notice them. 
While the very close relationship existing between the two more 
recently discovered forms ( schistacea and megarhyncha) has usually 
been recognized, from the occurrence of intermediate or doubtful 
specimens, the tendency has been strong to keep separate the two 
earlier described birds, mainly because no specimens with clearly 
intermediate characteristics have been recognized. Having had the 
very unusual opportunity of studying in the field the four forms in 
question, as well as of examining a very large series of specimens in 
the Smithsonian collection, many of which were collected by myself 
in connection with the United States Geographical Surveys west 
of the 100th Meridian, the conclusion seems to me to be unavoid- 
able that the four forms are but modifications of a single species, 
brought about through the agency of the laws of Geographical 
Variation. 
Considering first in their relations to each other the P. schistacea 
and P. megarhyncha , the first from the northern interior region, 
the latter from the Southern Sierras, we find that, though very 
distinct from each other when extreme samples of either form are 
selected, they yet in the full series before me grade directly to- 
gether, both in color and general size. Taking examples of mega- 
rhyncha from the southern Coast Range of California, which may 
be considered as the true home of the variety, that is, where its 
peculiarities attain their greatest development, we find them in 
their enormously developed bills and excessively lengthened tails, 
as well as darkened colors, to present such a totally different 
aspect that to liken them to schistacea seems almost absurd. 
Changing, however, our point of observation to the eastern slope 
of the Sierras, about Lake Tahoe, which is a region approaching 
somewhat closely the home of schistacea , we find that the Passe- 
rellas , though readily referable to megarhyncha , present very ap- 
preciable differences from those from the region just noted, and 
furthermore, that the variation is directly towards the schistacea 
type. The bills in specimens from the eastern slope are invariably 
and very decidedly smaller than in examples from Fort Tejon and 
that vicinity, though still much thickened when compared with 
specimens from the interior ( schistacea ). The color of the under 
