858 U. S. p. K. R. EXP. AND SURVEYS — ZOOLOGY — GENERAL REPORT. 



Sub-Family STERNINAE.— T h e Terns. 



Ch. — Bill rather long, usually slender, straight, sometimes with the upper mandible eurved at the tip, wliich is acutely 

 pointed; nostrils linear and pervious; wings elongated; primaries long and pointed, secondaries of moderate length; tail 

 rather long and in most species forked ; tarsi slender ; anterior toes have their webs emarginate, hind toe small ; claws moderate, 

 curved and acute. 



These birds are mostly found on the seacoast and neighboring bays, occasionally on rivers 

 and lakes ; they assemble in large numbers on the sand bars and points at the mouth of inlets, 

 are much on the wing, and are remarkable for their buoyant and easy flight. Their food 

 consists of small fishes and Crustacea, which they obtain by hovering over and suddenly darting 

 down upon ; although they thus seize their prey while in the water, they only occasionally 

 swim or rest upon its surface. 



This sub-family has been much subdivided into genera, but, as in the case of Larinae, I have 

 adopted the views of Mr. G. K. Gray and retained most of the species in Sterna. This reduces 

 the genera found in the United States to three, which may be characterized as follows : 



1. Sterna. — Bill rather long ; nostrils basal, with the frontal feathers extending up to 

 them ; tail forked ; interdigital webs emarginate. 



2. Hyduocheltdon. — Bill rather short ; frontal feathers reaching nearly to the nostrils, 

 which are basal ; tail emarginate ; interdigital webs deeply indented. 



3. Angus — Bill longer than the head ; the nostrils situated far forward of the frontal 

 feathers ; tail graduated ; interdigital webs full. 



STERNA, Linnaeus. 



Sterna, Linn. Syst. Nat. 1748. 



Ch. — Bill more or less strong, about the length of the head, the upper mandible slightly curved to the tip, which is narrow 

 and acute, the lower straight, with the junction of the crura about the middle ; the nostrils lateral and linear, with the frontal 

 feathers extending to the opening ; wings long, primaries narrow and tapering, the outer quill longest ; tail rather long and 

 more or less forked ; tarsi short ; toes small and slender, with the webs emarginate; hind toe short ; claws slightly arched and 

 acute. 



This genus is abundant in species, which vary much in size, but may readily be distinguished 

 by the following diagnoses ; 



Bill short and stout, entirely black ; mantle pale bluish gray ; under parts white ; tail 



not deeply forked; legs and feet black. Type of Gelochelidon, Bp S. aranea. 



Bill large and very strongs vermilion ; mantle pale bluish ash ; under plumage white ; 



tail moderately forked ; legs and feet black. Type of Hydroprogne, Kaup..(S'. caspia. 

 Bill large and strong, deep red ; mantle bluish gray ; beneath white ; tail forked ; legs 



and feet black... S. regia. 



Bill long, but rather slender, deep red ; mantle bluish gray ; under surface cream color ; 



tail deeply forked ; legs and feet black .^S*. elegans. 



Bill moderate, black, with the point yellow ; mantle light pearl blue ; lower parts white ; 



tail deeply forked ; legs and feet black. Tkallasseus of Boie S. acuflavida. 



Bill moderate, black, yellow at the point and base of lower mandible ; mantle light pearl 



blue ; below white ; tail deeply forked ; legs and feet orange yellow S. havellii. 



Bill moderate, black, with the base and point yellow ; mantle light bluish gray ; under 



parts of the same color ; tail deejjly forked ; legs and feet orange yellow... iS. trudeaui. 



