72 
ON THE CLASSIFICATION OF BIRDS. 
member among birds. Both mandibles are straight, 
and so much compressed as to resemble the blade of a 
knife — placed edgewise — more than any thing else: the 
upper mandible, indeed, is slightly thickened at its base, 
where the nostrils are situated ; but one quarter of its 
length appears broken off, so that the under mandible 
protrudes beyond the upper nearly an inch (fig. 37.). 
There are three, if not four, species of this most singu- 
lar genus, which in every other point of structure shows 
an intimate affinity to the ordinary Terns. Notwith- 
standing the length, even of the upper mamlible, the 
mouth of the bird itself is remarkably small : for it 
does not extend beyond the nostrils. Beyond that part, 
both tlie edges on the under mandible are quite sharp, 
but that which is uppermost is received into a very 
narrow groove on the corresponding piece, as if to pro- 
tect and preserve its sharpness. Not having had the 
opportunity of watching these birds alive, we can state 
nothing from personal observation ; but this is not to 
be regretted after the following account of their man- 
ners by ^Vilson. ‘'The sheerwater (Rhynchops niger L.), 
is formed for skimming, while on the wing, the surface 
of the sea for its food, which consists of small fish, 
shrimps, young fry, &c., whose natural haunts are near 
the shore and towards the surface. That the lower 
mandible, when dipt into and cleaving the water, might 
not retard the bird’s way, it is thinned and sharpened 
like the blade of a knife ; the upper mandible, being at 
such times elevated above water, is curtailed in its 
length, as being less necessary, but tai)ering gradually 
to a point, that, on shutting, it may suffer no oppo- 
