466 BULLETIN 50, UNITED STATES NATIONAL MUSEUM. 



Thalasseus imperator Coues, Proc. Ac. Nat. Sci. Phila., Dec, 1862, 538, in text 



(North America, but neither type locality nor type indicated). 

 S[tema} . . . cas/)ia, var. mperator Ridgway, Ann. Lye. Nat. Hist. N.Y., x, Jan., 



1874, 391 (Illinois). 

 Sterna caspia var. imperator Merrill (J. C), Proc. U. S. Nat. Mus., i, 1878, 172 



(Padre Island, Texas, breeding). 

 Sterna caspia . . . imperator Coues, Check List, 1873, no. 561. 

 Hydroprogne tschegrara imperator Mathews, Birds Australia, ii, pt. 3, Sept. 20, 



1912, 337 (North America). 

 Sterna regia (not of Gambel) Ridgwat, 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 Boie, Isis, viii, 1822, 563. (Type as designated by Wagler, 1832, 



Sterna cantiaca Gmelin.=iS'. sandvicensis Lathma.) 

 Thallasseus (emendation) Boie, Isis, vui, 1822, 880. 

 Actochelidon Kaup, Skizz. Entw.-Ges. Eur. Thierw., 1829, 31. (Type by mono- 



typy, Sterna cantiaca Gmelin=<S'. sandvicensis Latham.) 

 Pelecanopus Wagler, Isis, 1832, 277, 1225. (Type, Sterna pelecanoides King= 



Sterna bergii Lichtenstein.) 

 Pelanopus (emendation) Gray, Hand-list Birds, iii, 1871, 120. 



Large to very large SternidjB (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 elUptical, longitudinal; latero-frontal 

 antia intermediate in position between malar and mental antise, 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. Tail nearly 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 



