Henshaw on Selasphorus alleni. 
13 
of the earlier and, as a rule, far less particular compilers. The 
particularly narrow outer rectrices mentioned in all the accounts, 
upon which so much stress is laid by Mr. Elliot, by no means 
necessarily refers to the Green-backed form, though, as a matter 
of fact, the outer tail-feathers are much narrower in this species 
than in the other. The term is evidently one of contrast, the 
comparison being suggested by the extreme narrowness of the outer 
feathers as compared with the inner , w T hich are really very broad. 
In fact, there was nothing else to invite this particularity here. 
There being but one species known to all these authors, there was 
hence no need of comparative diagnosis other than that suggested 
by, the parts themselves. 
Gould, in his Monograph of the Trochilidce, after describing what 
was unquestionably the true Rufous-backed bird of Gmelin, the 
male with its “ back cinnamon brown,” adds : “ The above is the 
usual coloring, but I have occasionally seen fully adult males with 
the rich gorget in which the coloring of the back was totally dif- 
erent, being of a golden green* and presenting so great a contrast 
as almost to induce a belief that they were of a different species.” 
This latter allusion, as in the case of Professor Baird’s, is without 
doubt to the Green-backed form, its peculiarities of color being evi- 
dently the only difference noted by him. His figures, it is true, 
do not show the notched rectrix belonging to the Rufous form, 
- whence Mr. Elliot concludes that they must represent the other bird. 
But in color, as also, it is to be particularly noted, in the shape and 
size of the outer rectrices, they correspond exactly with the Rufous- 
back and differ irreconcilably from the Green-back. In short, they 
would not serve to identify the latter bird at all, but are good figures 
of the former in all respects except in the omission of the notch in 
the tail-feathers, in which particular they merely repeat the over- 
sight of the other authors. 
The Smithsonian possesses several specimens of the Rufous-backed 
form with its notched tail-feathers received directly from Mr. Gould. 
That his collection contained this form is therefore certain, if in- 
deed further confirmatory proof were necessary. The peculiarity 
of the notched tail-feathers was simply overlooked. 
But to return to the earlier writers ; the selection of Gmelin’s 
name is of itself suggestive that the bird he had in hand could 
* Italics my own. 
