282 REPTILES AND BIRDS. 
one on the other, forming two mandibles compressed into cutting 
blades, the upper being one-third shorter than the lower. In 
order to pick up the shrimps and small fishes on which they feed, 
these birds are obliged to skim the surface of the water, dipping the 
lower mandible of their bill, the upper mandible being kept open 
and clear of the water till aquatic insects or other small fry have 
entered upon the lower portion of it.* The singular form of their bills 
is also of service to them in opening such bivalve shell-fish as come 
in their way. They frequently watch these molluscs, and when they 
notice that the shell of the latter is slightly open, they plunge the 
lower mandible of their long bill into it; and cut the ligaments that 
hold the opposite sides of the bivalve together. The tenement 
being thus opened, there is no obstacle to their devouring the in- 
habitant. 
The representative of this species is the Scissors-bill (ARynchops 
nigra, Fig. 102), frequently called the Cut-water. It is about the size 
of a pigeon; its prevailing colour is white at the top of the head and 
black shoulders, a white band on the wings. These birds are very 
numerous in the West Indian seas. Like the Gulls and other sea 
birds, they occasionally form such dense flocks that they actually 
darken the sky for the space of a league. 
THE GULLS AND ALLIED SPECIES. 
This includes the well-known shore birds generally called Gulls, 
the most familiar of which are the Kittiwake, Common Gull, Black- 
backed Gull, and Skua. They are characterised by a light body, 
more or less compact ; neck of moderate length ; head ovate; bill 
shorter than the head, straight, compressed ; convex ridge on upper 
mandible, nasal groove long; lower mandible with the angle long 
and narrow ; mouth moderate ; tongue fleshy ; eyes small; legs gene- 
rally short; tibia bare; tarsus short, compressed; hind toe small; 
middle toe longest ; fore toe moderate in length and slender; con- 
necting membrane full, margins only concave ; claws generally small, 
arcuate, acute, and more or less compressed. 
These birds inhabit the sea-shore, along which they wander in 
search of food; the larger species preying on fish, crustacea, and 
mollusca, and the carcases of cetacea and other marine mammalia 
* Catesby says: ‘‘ These birds frequent near the sea-coast of Carolina. They 
fly close to the surface of the water, from which they seem to receive somewhat of 
food.” 
