858 
U. S. P. R. R. EXP. AND SURVEYS-ZOOLOGY-GENERAL REPORT. 
Sub-Family STERNINAE.—T h e Terns. 
Ch.—B ill rather long, usually slender, straight, sometimes with the upper mandible curved at the tip, which 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 hays, 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. R. 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.—B ill rather long ; nostrils basal, with the frontal feathers extending up to 
them; tail forked; interdigital webs emarginate. 
2. Hybrociielidon.—B ill rather short; frontal feathers reaching nearly to the nostrils, 
which are basal; tail emarginate ; interdigital webs deeply indented. 
3. Anous.—B ill longer than the head ; the nostrils situated far forward of the frontal 
feathers ; tail graduated ; interdigital webs full. 
STERNA, Li naeus. 
Sterna, Linn. Syst. Nat. 1748. 
Ch.—B ill 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 he 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 Crelochelidon, Bp. S. aranea. 
Bill large and very strong, vermilion ; mantle pale bluish ash; under plumage white ; 
tail moderately forked ; legs and feet black. Type of Hydroprogne , Kaup..& caspia. 
Bill large and strong, deep red ; mantle bluish gray ; beneath white ; tail forked ; legs 
and feet black.. S. regia. 
Bill long, hut 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. Tliallassens 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. liavellii. 
Bill moderate, black, with the base and point yellow ; mantle light bluish gray; under 
parts of the same color ; tail deeply forked ; legs and feet orange yellow... S. trudeaui. 
