244 
MARSH TERM. 
mandible with the dorsal line nearly straight to the anterior edge of the 
nostrils, then arcuato-declinate, the ridge rather broad and rounded at the 
base, narrowed toward the end ; the sides sloping at the base, nearly erect 
and convex toward the end, the edges sharp and inflected, the tip although 
narrow somewhat obtuse. Nasal groove comparatively short ; nostrils basal, 
oblong, direct, pervious. Lower' mandible with the angle very narrow and 
acute, extending to beyond the middle, the outline of the crura a little con- 
cave, that of the rest ascending and straight, a prominence or angle being 
formed at their junction as in Gulls, the sides erect and slightly convex, the 
edges sharp and inclinate, the tip acute, the gap line straight for half its 
length, then slightly arcuato-declinate. 
Head of moderate size, ovate ; neck of moderate length ; body slender. 
Feet small ; tibia bare for nearly half an inch ; tarsus very short, compressed 
anteriorly scutellate ; toes small, slender ; the first extremely small, the third 
longest, the fourth considerably shorter ; all scutellate above, the anterior 
connected by reticulated webs, of which the inner is more deeply emargi- 
nate. Claws a little 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 ten and a half twelfths of an inch shorter, 
the rest rapidly graduated ; secondaries short, incurved, obliquely rounded, 
some of the’inner proportionally longer and narrower. Tail of moderate 
length, forked, of twelve feathers, of which the middle are rounded and an 
inch and seven-twelfths shorter than the outer, which tapers to a narrow 
but obtuse point. 
Bill black, as are the feet. Iris brown. The upper part of the head, the 
nape, and part of the hind neck, deep black ; sides of the head,. including a 
line margining the base of the upper mandible, fore neck, and all the lower 
parts white ; upper parts pale greyish-blue ; the edges of the wings whitish ; 
the primary quills hoary on the outer web, deep grey on the inner, but with 
a large portion toward the base lighter, the shafts and those of the tail- 
feathers white ; the tail is of a paler tint than the back, and the outer 
feather is nearly white. 
Length to end of tail 14 inches ; extent of wings 34 ; bill along the ridge 
l r 6 2 , along the edge of lower mandible 2 ^ wing from flexure 12 T V ; tail to 
end of middle feather 3 T 4 2 , to end of lateral feather 4H ; tarsus li ; first toe 
.,3f, its claw y; middle toe its Claw f-|. 
A female from the mouths of the Mississippi, April 1, 1837. On the roof 
of the mouth are three longitudinal ridges ; the posterior aperture of the 
nares is linear, with an anterior slit ; the tongue slender, tapering, 1 inch 2 
