some South- American Birds. 279 



also from those recorded by Mr. Hudson in tlie ' Proceedings' 

 of the Zoological Society and ' Argentine Ornithology/ and 

 from the collections made by Miss I. G. Runnacles. 



Unfortunately, with regard to the eggs of M. rufo-axillaris 

 and M. badius collected by Mr. Hudson and now in the British 

 Museum, they were taken at a time when Mr. Hudson wa^ 

 very doubtful in his own mind as to their identity, as 

 shown by his letters iu the P. Z. S. for 1870, 187.2, and 

 1874. 



Hence the only eggs which I positively know to be 

 authentic are those collected by Miss Runnacles and myself, 

 and I have based my conclusions mainly on those. 



The eggs of M. bonariensis are distinct enough and cannot 

 easily be confounded with either those of M. rufo-axillaris or 

 those of M. badius, even w hen found together in the same nest. 



There appears to be about nine varieties of colouring, 

 varying roughly from pure white, with or without markings, 

 to a fawn-colour or flesh-colour, with more or less numerous 

 markings. 



So far as we know at present, the following are the foster- 

 parents of this species, though the list is probably not 

 yet complete: — Mimus modulator, Troglodytes hornensis, 

 Furnarius rufus, Anthus correndera, Serpopha(/a nigricans, 

 Mihulus tyrannus, Machetornis rixosa, Tardus rujiventris, 

 Synallaxis hadsoni, Brachjspisa pileata and 3Iolot/n-us badius. 



It is to distinguish between the eggs of M. rufo-axillaris 

 and M. badius that the real difficulty has hitherto existed, 

 and I have arrived at my conclusions from knowing the 

 authenticity of the series before me and from the evidence of 

 the individual eggs taken from carefully determined nests. 



The main mistake has arisen from taking it for granted 

 that eggs found in the nests of M. badius were those of 

 that species. This is by no means the case, as the majority 

 of eggs found in the nests of 31. badius (where both the 

 parent birds are attendant) are really the eggs of M. rufo- 

 axillaris, as is conclusively shown by comparing specimens 

 with those taken from nests of other birds in which M. rufo- 

 axillaris is known to place its eggs. 



