LARID^ — THE G-ULLS AND TERNS — LARUS. 229 



Larus schistisagus. 



THE SLATY-BACKED GULL. 



? Larus (Dominicanus) fusccsccns, Bruch, J. f. 0. 1853, 100 (part). 



Larus cachinnans, Kittl. Deiikw. I. 1858, 336 (nee Pall. 1826). — Stejn. Naturen, 1884, 6. 



Larus argentatus, var. cachinnans, Schrenck, Reise, Amurl. I. 1860, 504. 



Larus marinus, Swixir. Ibis, 1874, 165 (nee Linn.). — Saunders, P. Z. S. 1878, 180. — Blakist. 

 & PiiYER, Ibis, 1878, 217; Trans. Ass. Soc. Jap. VIII. 1880, 189 ; ib. X. 1882, 104. — Seeb. 

 Ibis, 1879, 24. — EiDGW. Bull. Nutt. Orn. Club, 1882, 60. — Bean, Pr. U. S. Nat. Mus. 1882, 

 168. — Nelson, Cruise of the Corwin, 1883, 107. — Blakist. Amend. List B. Jap. 1884, 20. 



Larus pclagicus, Taczan. Bull. Soc. Zool. France, 1876, 263 (nee Bruch) ; Orn. Faun. Vost. Sibir. 1877. 



? Larus affimis. Nelson, Cruise of the Corwin, 1883, 107 (Plover Bay). 



Larus schistisagus, Stejneger, The Auk, Vol. I. July, 1884, 231. 



Hab. North Pacific, chiefly on the Asiatic side. Japan (Blakiston & Pryer, Saunders, 

 and Seebohm, U. c.) ; Amoor River (Schrenck) ; Behring Island and Petropaulski, Kamtschatka 

 (Stejneger) ; Plover Bay ? (Nelson) ; Unalashka (Bean) ; Herald Island, Arctic Ocean, and 

 Port Clarence, Alaska (Ridgway, 1. c). 



Sp. Char. Adult $ (No. 92825, U. S. Nat. Mus., Behring Island, Kamtschatka, May 5, 1883 ) : 

 Head, neck, rump, ujiper tail-coverts, tail, and entire lower parts pure white ; mantle and wings 

 deep plumbeous, or bluish slate-gray, much darker than in L. occidentalis, and altogether moi'e 

 bluish than in L. viarinus. Four outer primaries slaty black, more grayish basally and on the 

 inner webs, the latter fading into bluish gray toward the edge ; outer quill with the terminal 2.10 

 inches (measured along the shaft) white, both webs with a small blackish spot on the edge, about 

 .40 of an inch from the tip ; second quill Avith the terminal white spot only .40 of an inch in 

 extent, but the inner web with a large oval spot of white, .90 of an inch long, and extending 

 entirely across, and situated .50 of an •inch anterior to the terminal white spot ; third cj^uill with 

 the terminal white spot about the same size as that on the second, the inner web with a grayish 

 white space, beginning about 1.60 inches from the tip, abruptly defined, with a deeply convex out- 

 line, against the black subterminal portion, but not distinctly contrasted with the plumbeous-gray of 

 the remaining portion of the web ; fourth quill simihu' to the third, but the white spot ratlier more 

 distinct, and beginning only 1.30 inches from the tip ; fifth quill similar, but with the white spot 

 on the inner web still larger and still nearer the tip (only I.OO inch), and the outer web dark 

 plumbeous-gray to within about 1 .50 inches of the end, the extremity of this grayish portion obtusely 

 wedge-shaped, and fading into white at the extremity ; sixth quill without any distinct black spot 

 on the inner web, which is white for about 1.80 inches (measured next the shaft) from the tip, the 

 white rather abruptly defined against the plumbeous of the anterior portion ; outer web white for 

 .60 of an inch, then slaty black for about .70 of an inch (measured along the edge), the anterior 

 outline deeply concave, and enclosing a rather indistinct grayish white space, which deepens gradu- 

 ally into the dark plumbeous-gray preceding it. Remaining primaries without any black, being 

 uniform deep plumbeous, with very broad and rather abrupt white tijris. " Iris clear naples yellow, 

 or rather a yellowish cream-color ; bill deep gamboge-yellow, with whitish tip and toniia ; an 

 orange-red spot on each side of the lower mandible ; angle of the mouth yellowish flesh-color ; 

 naked eye-ring reddish violet gray ; feet pinkish flesh-color, nails horny black, with whitish tips " 

 (Colors of freshly killed hird, fide Stejneger, MSS.). 



"Wing, 18.10 inches; tail, 7.50 ; culmen, 2.35; depth of bill through base, .80, at angle, .90; 

 tarsus, 2.75 ; middle toe, 2.40. 



This species is apparently the North Pacific representative of L. marinus, from which it may 

 easily be distinguished by the different color of the mantle, which is of a deep bluish slate, or 

 plumbeous, without any of the brown tinge that is always seen in marinus. The latter has no gray 

 "wedge" on the inner web of the first primary, and has on the second quill a subapical white 

 crossbar. The white subapical spot on the third primary of schistisagus is altogether wanting in 

 marinus. 



From L. cachinnans the present bird differs in having a very much darker mantle {cachinnans 

 being decidedly paler than occidentalis, while schistisagus is much darker), flesh-colored instead of 

 yellow feet, in being of larger size, and in possessing other marked characters. 



