LARiD.i:— Till-: gulIjS and terns. 223 



The species belon2:ing to eastern North America may be char- 

 acterized as follows: 



A. Adult with the entire head, neck, lower parts, and tail pure white. (Lams, Limn.) 



(I. Mantle vcn-y palc^ pearl-blue; primaries the same, fadinK into white toward the ends. 



1. L. plaucus. Win«, li!.7.j-18.«0 inches; culmen, 2.15-2.(i5; depth of bill through the 

 angle, .75-1.00; tarsus, 2.30-3.00; middle toe, 1.95-2.50. Eyelids in summer adult, red- 

 dish purple; feet flesh-color. 



2. L, leucoptems. Wing, 15. JO-lO.ijQ inches; culmen, l.(!.5-1.90; depth of bill through 

 angle, .(;i>-.70; tarsus, 2.05-2.20; middle toe, \.7^>-^.'J5. Eyelids in summer adult, flesh- 

 color; feet inclining to orange-red. 



b. Mantle pale pearl-blui*; pi-imaries similar, but abruptly tipped with white. 



3. L. kumlieni. Five outer primaries marked with slate-gray spaces immediately be- 

 fore the white tips; color of the mantle as in Z.. /eucop^erw.s, and size about the 

 same. Eyelids in summer adult reddish purple, or purplish flesh-color; feet flesh- 

 color. Wing, 15,00-17.00 inches; culmen. 1.60-1.90; depth of bill through angle .5.5-66; 

 tarsus, 2.10-2.40. Ilab. North Atlantic coast, breeding in Cumberland Soun'i, and 

 migrating south in winter to Nova Scotia, New Brunswick, and New York. 



c. Mantle dark slate-color, the primaries marked with black and white terminally. 



4. L. marinus. Wing, 17.60-19.50; culmen. 2.40-2.60; depth of bill at angle; .98-1.05; 

 tarsus, 2.70-3.10. Uab. Coasts of the North Atlantic. 



d. Mantle some shade of bluish gray ; primaries marked with black and white at and 



near the end. 



5. L. argentatus.. Wing, 15.75-17.90 inches; culmen. 1.85-2.20: depth of bill through 

 angle. .70-.80; tarsus, 2.30-2.72; middle toe, 1.85-2.25. Mantle pale pearl-blue. BiU 

 deep yellow, the mandible with red subterminal spot; eyelids yellowish; iris sil- 

 very white or pale yellow; legs and feet flesh-color. 



6. L. argentatus smithsonimua. Similar to true L. argentatus, but averaging larger 

 and with less white and more black on primaries. Wing, 16.25-17.50; culmen, 1.95- 

 2.50; depth of bill through angle, .68-.85; tarsus. 2.30-2 80: middle toe, 1.85-2.25. 



7. L. delaw^arensis. Mantle pale pearl-blue (much as in i. a?-£7en(rt<MS'. Wing, 13.60- 

 15.75 inches; culmen. 1..55-1.75; depth of bill through angle, .50-.65; tarsus, 1.90-2.45; 

 middle toe, 1 .30-1.60. Bill greenish yellow, crossed near the end by a blackish 

 band, the tip sometimes tinged with orange: eyelids vermilion-red; iris clear pale 

 yellow; legs and feet pale yellow, sometimes tinged with greenish. 



8. L. canus. Mantle pale ashy blue (as in L. brachyrhynchus). Wing, 13.90-1450 

 inches; culmen, 1.35-1.60; depth of bill through angle, .45-50; tai-sus, 1.90-2.25; mid- 

 dle toe, 1.35-1.45. Bill greenish olivaceous (in the dried skin), the terminal third 

 yellow; eyelids vermilion- red; iris gi-ayish brown; legs and feet yellowish green. 

 Hab. Palaarctic region; accidental in Labrador' 



B. Adult with the head and upper part of the neck black or slaty in summer, forming a 



well defined "hood;" plumage of the lower parts rose-tinted; size medium to very 

 small; the bill slender. (Chroicocephalus, Eyton.) 

 a. Tarsus longer than the middle toe and claw. 



9. L. atricilla. Bill and feet dark brownish red, the former sometimes tipped with 

 brighter red; eyeUds dull red; iris dark brown; hood dark sooty-slate; mantle 

 deep plumbeous- slate. Wing, about 13.00 inches. 



6. Tarsus shorter than the middle toe and claw. 



10. L. franklinii. Bill and feet carmine-red; iris dark brown; hood plumbeous-black; 

 mantle deep bluish plumbeous. Wing, about 11.25 inches. 



11. L. Philadelphia. Bill uniform deep black; legs and feet fine orange-red in summer, 

 flesh-color in winter; iris dark brown; hood dark plumbeous; mantle delicate 

 pearl-blu'"- Wing, about 10.25 inches. 



12. L. m-'nutus. Bill reddish dusky; legs and feet vermilion- or coral-red; hood deeo 

 black; mantle delicate pearl-gray; primaries without any black markings. Wing, 

 about 8.75-9.00 inches. Hab. Palaearctlc Region; accidental in Massachusetts and 

 Bermudas. 



