BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 129 



to the original description of the Chuiia in the Proceedings of the 

 Zoological Society of London his name must have appeared later 

 than Hartlaiib's notice of it. Hartlaiib remarks that the subgenus 

 Chung a is proposed by Burmeister, but no reference to such action 

 is at present known. 



Order CHARADRIIFORMES 

 Family STERCORARIIDAE 



STERCORARIUS PARASITICUS (Linnaeus) 



Larus parasiticus Linnaeus, Syst. Nat., ed. 10, vol. 1, 1758, p. 136. (Coast 

 of Sweden.) 



Three specimens were taken 15 miles south of Cape San Antonio 

 on the eastern coast of the Province of Buenos Aires, a female on 

 November 4, 1920, and two males on November 7. The female is 

 Avhite below and on the hind neck, with slightW indicated grayish- 

 brown streaks on the neck, both in front and behind. Broken bars 

 of a similar color cross the breast and to a less degree the abdomen, 

 and the under tail coverts are barred with fuscous and white. The 

 two males represent the dark phase and are dull in color throughout. 

 These specimens apparently are in their second year, as traces of 

 the first-year plumage of the juvenile are evident. The primaries 

 and rectrices are worn and have not yet been molted. 



While adult jaegers may be named with ease, it is trite to remark 

 that identification of specimens representing the immature stages is 

 attended with more or less difficulty. With regard to the two 

 smaller forms, parasiticus and longicaudu^, it may be necessary to 

 have recourse to more than one character in order to be definitely 

 sure that identification is correct. The following brief summary 

 (for which I make no claim of originality, as it is a combination 

 of matter given by Ridgway, Coues, Saunders, and Mathews) may 

 be of assistance in naming birds of this group : 



a \ Bill higher than wide at base ; wing usually more than 350 mm. ; in adult 

 the middle pair of rectrices broad throughout, twisted. (Subgenus 



Coprotheres) pomarinus. 



a *. Bill not higher than wide at base, wing less than 345 mm. ; in adult the 

 middle pair of rectrices straight. 

 W. Length of horny cere (supranasal saddle) decidedly greater than length 

 of dertrum; tarsi and feet black; three or more outermost primaries 



with shafts ivory yellow. (Subgenus Stercorarius.) parasiticus. 



6^ Length of horny cere (supranasal saddle) not gi-eater than length of 

 dertrum; tarsi wholly or in part light in color, feet black; only two 

 outermost primaries mth shafts ivory yellow (the shaft of the third 

 sometimes light, but with a brownish tinge for at least part of its 

 length). (Subgenus Atalolestris.) longicaudus. 



