466 BULLETIN 50, UNITED STATES NATIONAL MUSEUM, 
Thalasseus imperator Cours, Proc. Ac. Nat. Sci. Phila., Dec., 1862, 538, in text 
(North America, but neither type locality nor type indicated). 
S[terna] . . . caspia, var. imperator Ripaway, Ann. Lyc. Nat. Hist. N.Y.,x, Jan., 
1874, 391 (Illinois). 
Sterna caspia var. imperator Merrit (J. C.), Proc. U. 8. Nat. Mus., i, 1878, 172 
(Padre Island, Texas, breeding). 
Sterna caspia . . . imperator Covzs, Check List, 1873, no. 561. 
Hydroprogne tschegrava imperator MatHews, Birds Australia, ii, pt. 3, Sept. 20, 
1912, 337 (North America). 
Sterna regia (not of Gambel) Rripeway, Bull. Essex Inst., v, 1873, 173 (Great Salt 
Lake, Utah, summer); vii, 1875, 16 (Truckee Valley, Nevada, May), 23 (Sink 
of Humboldt River, Nevada, summer); Orn. Fortieth Parallel, 1877, 639 
(Sink of Humboldt, Great Salt Lake, etc.). 
Genus THALASSEUS Boie. 
Thalasseus Bors, Isis, viii, 1822, 563. (Type as designated by Wagler, 1832, 
_ Sterna cantiaca Gmelin. =S. sandvicensis Lathma.) 
Thallasseus (emendation) Bor, Isis, viii, 1822, 880. 
Actochelidon Kaur, Skizz. Entw.-Ges. Eur. Thierw., 1829, 31. (Type by mono- 
typy, Sterna cantiaca Gmelin=S. sandvicensis Latham.) 
Pelecanopus Waauzr, Isis, 1832, 277, 1225. (Type, Sterna pelecanoides King= 
Sterna bergti Lichtenstein.) 2 ae 
Pelanopus (emendation) Gray, Hand-list Birds, iii, 1871, 120. 
Large to very large Sternide (wing 268-391 mm.) with long and 
moderately stout to rather slender bill, deeply forked tail with lateral 
rectrices attenuated, occipital feathers elongated, lanceolate, form- 
ing a distinct crest, and inner webs of primaries distinctly bicolored, 
Bill long and relatively rather (sometimes decidedly) slender, its 
- depth at base equal to between one-fourth and one-third the dis- 
tance from anterior end of nostril to tip of maxilla, the exposed 
culmen decidedly to much longer than combined length of tarsus 
and middle toe with claw; gonys shorter to much longer than 
mandibular rami; nostril close to but not in contact with latero- 
frontal antia, linear or narrowly elliptical, longitudinal; latero-frontal 
antia intermediate in position between malar and mental antiz, but 
rather nearer the latter. Wing long and pointed, the longest primary 
(outermost) exceeding distal secondaries by more than twice the dis- 
tance from tips of the latter to bend of wing. Tailnearly to more than 
half as long as wing, forked for a little less to decidedly more than 
half its length, the lateral rectrices slender and attenuated, but not 
acuminate, terminally. Tarsus decidedly longer than middle toe 
without claw; webs between anterior toes slightly but distinctly 
incised. 
Plumage and coloration.—Occipital and nuchal feathers conspicu- 
ously elongated and lanceolate, forming a distinct erectile crest. 
Adults with pileum uniform black, the forehead and crown mostly 
white in breeding season; upper parts pale gray; under parts, rump, 
and tail white, the first often tinted with eosine pink; inner webs of 
primaries distinctly bicolored. Downy young with upper parts 
streaked or longitudinally flecked with blackish 
