854 



U. S. p. E. E. EXP. AND SUEVEYS — ZOOLOGY— GENEEAL EEPOET. 



These birds mostly inhabit the north. They assemble in flocks, and are most graceful birds 

 on the wing. They possess great powers of flight, being able to contend with the strongest 

 gale. Medium in size. 



Three species belonging to this genus are found in the United States. They may be 

 distinguished as below : 



Mantle light pearl gray ; bill moderate, pale greenish yellow ; tarsi moderate ; hind toe 



rudimental B. tridactylus. 



Mantle light pearl blue ; bill rather long ; greenish at the base, with the point yellow ; 



hind toe short; more developed than in the above species B. septentrionalis. 



Mantle pale leaden gray ; bill short and strong, bright yellow ; hind toe short.i?. nivea. 



EISSA TEIDACTYLUS, B o n a p . 



Tlie Klttlwate G«U. 



Larus tndactylus, Linn. Syst. Nat. I, 1766, 224.— Bonap. Syn. 1828, No. 297.— Rich. &Sw. II, 1831, 423.— 



NuTT. Man. II, 1834, 298.— Acd. Birds Am. VII, 1844, 146 ; pi. ooccxiiv. 

 Rissa tridactylus, Bon. List, 1838.— Ib. Cons. Av. II, 1856, 225.— Bruch, Cab. Jour. 1855, 284. 

 Larus rissa, BrUnn. Orn. Bor. 1764. 



Sp. Ch. — Mult. Head, neck, entire under plumage, rump, and (ail white ; back and wings light bluish gray ; the ends of the 

 five outer primaries and the outer web of the first black ; the fourth and fifth have small white tips ; bill greenish yellow ; iris 

 reddish brown ; legs and feet brownish black with a green tinge . 



Young. The head is white, marked on the hind head and neck with bluish gray ; a spot of the same color over the ears ; a 

 narrow crescent of black in front of the eye. Wings and shoulders marked with black ; primaries black. Tail white, with a 

 sub-terminal black band. Bill black ; rest of the plumage same as in the adult. 



Length, about 17 inches ; wing, 12 ; tail, 51 ; bill, 1| ; tarsus, 11. 



Hab. — Pur countries ; Labrador ; southern coast in winter. 



EISSA SEPTENTEIONALIS, Lawrence. 



The Worth Paclflc Kittlwoke, 



Rissa septentrionalis, Lawr. Ann. Lye. N. Hist. N. Y. VI, 1858, 265. 



Sp. Ch. — Adult. Head, neck, under surface, and tail pure white. Back and wings light pearl blue ; first primary black for 

 about half its length from the end ; a white spot one and a half inches in length crosses both webs near the end, which is black ; 

 second primary black for about one third its length ; also with a white spot (but smaller) inside the black tip ; the next five 

 primaries are black at their ends, with white tips ; the black decreases inwards, existing as a spot only on the seventh ; basal 

 part of the primaries bluish ash, becoming white where it joins the black ends, except on the first and second ; secondaries and 

 tertiaries ending with white ; bill dusky green at the base for two-thirds its length ; remainder yellow, which deepens to orange 

 on the ridge of the upper mandible and angle of the lower ; legs and feet yellowish green. Length, 17j inches ; wing, 13J 

 tail, 51 ; bill, li ; tarsus, 1^. 



Hah. — Pacific coast of North America ; Puget's Sound. 



Two specimens are in the collection. 



List of specimens. 



