MARSH TERN. 85 



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 

 1 T 6 2, along the edge of lower mandible 2 T \; wing from flexure 12 T V; tail to 

 end of middle feather 3 T 4 2, to end of lateral feather 4{i; tarsus H; first toe 

 f|, its claw ||; 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 



Vol. VII. 12 



