HA YELL’S TERH. 
263 
minence or angle being formed at their junction, as in Gulls, the sides erect 
and slightly convex, the edges sharp and inclinate, the tip acuminate, the 
gap-line slightly arcuate. 
Head of moderate size, ovate ; neck of moderate length : body slender. 
Feet small; tibia bare for seven-twelfths of an inch; tarsus very short, 
compressed, anteriorly scutellate ; toes small, slender ; the first extremely 
small, the third longest, the fourth much longer than the second; all scutel- 
late above, the anterior connected by reticulate webs, of which the inner 
is more deeply emarginate. Claws moderately arched, compressed, very 
slender, that of the middle toe much larger, and having its inner edge 
somewhat dilated. 
Plumage soft, close, blended, very short on the fore part of the head. 
Wings very long, narrow, and pointed; primary quills tapering to an obtuse 
point ; the first longest, the second half an inch shorter, the rest rapidly 
graduated ; secondaries short, incurved, obliquely pointed, some of the 
inner proportionally longer and narrower. Tail of moderate length, deeply 
forked, of twelve feathers, of which the middle are rounded, and three 
inches and a quarter shorter than the outer, which taper to a slender point. 
Bill black, with the base of the lower mandible tinged with brown, and a 
very small portion of the tip yellowish. Iris brown. Feet orange-yellow ; 
claws dusky. Surrounding the eye, and extending toward the nape, is a 
broad band of black ; the fore part of the head, the lower eyelid, and all the 
under parts are pure white ; the hind parts of the head and the nape are 
dusky-grey, mixed with white. The rest of the upper parts are light 
greyish-blue, excepting the rump, which is white, the primary coverts and 
quills as well as the tail-feathers and their coverts are hoary, with the shafts 
white ; but five of the quills are dusky on the outer web, on the inner along 
the shaft, and on the inner margin toward the end. 
Length to end of tail 151 inches; bill along the ridge 1 T 7 ^, along the edge 
of lower mandible 2 T 4 2 ; wing from flexure 10 , | ; tail to end of middle 
feather 2 T 8 2 , to end of longest feather 6 ^ 2 ; tarsus y^; hind toe T 3 2 , its claw 
T V, middle toe If, its claw y 4 ^. 
This species differs from the Marsh Tern, Sterna anglica, in being less 
robust, in having the bill a little longer and much more slender, its height 
at the angle being T 3 ^, whereas in that species it is y 4 ^; in having the tarsus 
shorter and much more slender, the feet yellow instead of being black, the 
claws more slender, and the tail more deeply forked. 
The figure in the plate, which is that of an adult bird yet in its winter 
plumage, has the lateral tail-feathers obliquely truncate, but this was caused 
by accident, for these feathers in my other specimens run to a narrow point. 
My specimens from Texas are also in their winter plumage. One of them 
