BIRDS OF NOBTH AND MIDDLE AMERICA. 517 



at base, 7.37; tarsus, 21.08; middle toe, 13.21. (Tj^pe, no. 131680, 

 U. S. Nat. Mus., Cocos Island, February 28, 1891; C. H. Townsend.) 



Adult female. — Pileum and hindneck dusky, the feathers edged with 

 light olive, producing distinct though narrow streaks; back and scap- 

 ulars with dusk}" centers and broad margins of bufiy olive; rump plain 

 buffy brownish or isabella color, the upper tail-coverts similar but 

 with rather indistinct dusk}' centers; wings dusky with more or less 

 distinct light brownish edgings, the middle and greater coverts broadh' 

 tipped with light cinnamon or dull ochi'aceous-buff, producing two 

 distinct bands; tail duskj', the feathers narrowly edged with light 

 olivaceous and narrowly tipped with light cinnamon; sides of head 

 and under parts pale j^ellowish buff, the abdomen inclining to pale 

 maize j^ellow and the flanks washed with vuHtj brownish; sides of head 

 thickly and finely streaked with dusky, especially on auricular region, 

 where the ground color is more olivaceous; chin and throat narrowlj^ 

 streaked with dusk}'; chest, upper breast, sides, and flanks broadly 

 streaked with dusky, some of the streaks on chest almost black; bill 

 pale brownish (still paler on mandible), becoming dark brownish at 

 tip; legs and feet as in adult male; length (skin), 116.84:; wing, 63.60; 

 tail, 40.39; exposed culmen, 12.45; depth of bill at base, 6.10; tarsus, 

 20.83; middle toe, 12.95. (No. 131690, U. S. Nat. Mus., " 9 ?," Cocos 

 Island, February 28, 1891; C. H. Townsend.) 



Immature males are variously intermediate between the adult male 

 and supposed adult female, as described above. One (No. 131682, 

 same date, etc.) is ipostly uniform black, but the feathers of the rump 

 are broadlj^' margined with olive-brown, and the under parts posterior to 

 the chest a mixture of black and dull yellowish white (mediall}-) and 

 pale brownish (laterally). In this specimen the bill is wholl}' black, 

 thus showing that in this species there is the same curious variation in 

 the color of the bill, without regard apparently to age or season, that 

 exists in the species of Geospiza and Certhidea. 



Cocos Island, Pacific Ocean, near Bay of Panama. 



Cocornis agassizi Totvnsend, Bull. Mus. Comp. Zool., xxvii, no. 3, July, 1895, 

 123, colored plate (Cocos I.; coll. U. S. Nat. Mus.). 



Genus ACANTHIDOPS Ridgway. 



Acanthidops^ Bidqway, Proc. IT. S. Nat. Mus., iv, sig. 21, Mar. 10, 1882, 335. 

 (Type, Acanthidops bairdi Ridgway.) 



Siinilar to Ilaplospiza Cabanis but more slender, the bill especialty; 

 tarsi relatively longer; nostrils less exposed. 



Bill about as long as the middle toe, cuneate in all its profiles, some- 

 what swollen basally, the culmen and lateral outlines decidedly con- 

 cave in the middle portion; mandibular tomia very stronglj^ inflexed, 



^'AKavBii, ido'; = Acanthis, and d>ip= appearance. 



