ORNITHOLOGICAL CLXJB, 
55 
from the interior, I have seen at least two hundred adult males, and 
they all possessed the bright rufous back, only an occasional individ- 
ual showing a faint trace of the green. In California, however, where 
the /S', rn/tts occurs in its typical condition, that is, with an unmixed 
rufous back, specimens are not uncommonly found which exhibit a 
strong approach to the coloration of /S. alleni. In these the rufous 
is seen to be mixed with green in varying proportions. Beyond a 
certain point they appear never to pass, and all such specimens have 
the peculiar tail characters of S. rufus as strongly marked as in the 
most typical examples of the species. We find .the same difference 
between specimens of S. rufus taken in California and on the 
west coast generally, and those from the interior, that usually ob- 
tains in species possessed of a similar range, — that is, the coloration 
is appreciably darker. The locality of specimens, whether from the 
coast or the interior, may by this means be readily told. 
In Mexico only the S. rufus appears to occur, and Mr. A. Boucard 
informed Mr. Ridgway that, having examined hundreds of the Selas- 
phorus from there, he had never seen an example of the Green- 
backed form, which, however, he was familiar with from California. 
One of the strongest proofs of the specific distinctness of the two 
is seen in the fact that the two birds, in their typical condition, 
occur at the same locality and at the same season. Both breed about 
Nicasio (situated about twenty-five miles north of San Francisco), 
though Mr. Allen finds the S. alleni very much more abundant than 
the other. Thus, during the present season (1877), he has shot 
about forty-five of the former bird, and has only succeeded in taking 
four of the rufous-backed species. Last year’s experience was a 
similar one. 
This gentleman, whose investigation of these two birds has 
extended over several years, and who, it is but proper to state, has 
always believed them to be distinct, has found a constant difference 
in size, the /S', alleni being the smaller. Such I find to be the case 
in the several specimens I have measured, and the discrepancy 
between them is quite considerable when the diminutive size of the 
birds of this family is taken into account. 
Habits. I am in possession of but few notes bearing upon the 
habits of this Hummer. Mr. Allen remarks incidentally in a letter 
that the Green-backs are much the livelier and more active of the 
two, keeping constantly in the open, and always perching upon the 
most prominent dead twigs they can find. Their extreme shyness, 
