1873.] 81 [Ridgway. 



above cited, but is to be referred rather to the gray phase of M. rufi- 



collis. 



5. Micrastur concentricus (Illiger). 

 Falco concentricus Illig. in Mus. Berol. 

 Nisus concentricus Lesson, Tr. d'Orn. 



Climacocercus concentricus Caban., in Erich. Archiv. 1844, I, 265. — 

 Id. Tschudi, Fauna Per. 18 and 98. — Id. Schomb., Reise Guiana, 

 in, 735. — Burm., Thiere Bras, n, 86. 

 Circaetus (Herpetotheres) concentricus Kaup, Isis, 1847, 260. — Id. in 



Trosch. Arch. 1850, i, 37. 

 Micrastur concentricus Gray, Gen. 28, (excl. syn. Vieill.). — Bonap., 

 Consp. i, 30 (excl. syn. Vieill.). — Id. Rev. Zool. 1854, 537.— 

 Strickl, Orn. Syn. I, 123 (in part). — Pelzeln, Orn. Nov. 1865, 

 1865, 9 (diagnosis, corrected synonomy and remarks). — Id. 

 Orn. Bras., 399. 

 Falco senex Natterer, in Mus. Vindob. (fide Pelzeln). 

 Micrastur gilvicollis Scl. and Salv., P. Z. S. 1869, 368 (excl. synon- 

 omy). 

 Sp. ch. Wing, 7.10-7.55; tail, 6.30-6.50 ; culmen, .60; tarsus, 

 2.25-2.45; middle toe, 1.00-1.08. Adult. Above uniform plumbe- 

 ous-ashy, sometimes more bluish anteriorly. Tail black, with 3-4 

 very narrow, distant bars of white. Beneath white, the breast, sides, 

 and abdomen barred with slate-color; tibise with t fewer, narrower 

 bars of the same ; crissum and anal region immaculate, and lining of 

 the wing barred only along the exterior border. Throat plain pale 

 ashy, or ashy white, this gradually paler than the cheeks, which are 

 lighter ash than the crown. 



Specimens examined. Philad. Acad., 5 ; Boston Society, 1 ; N. Y. 

 Mus., 1 (Amazon). Total, 7. 



Hab. Whole of Continental Tropical America. Brazil, (Mus. Bos- 

 ton Soc.) ; Amazon, (N. Y. Mus.) ; Mexico, (Bonaparte) ; Bolivia, 

 (D'Orbigny) ; Bahia, Guiana, Rio Negro, and Rio Janeiro, (Pelzeln). 

 With a general or superficial resemblance to the gray phase of M. 

 ruficollis (" gilvicollis" and " zonothorax ") this very distinct species 

 may be immediately distinguished without comparison, by having the 

 outer toe shorter than the inner, the tail shorter than the wing, and 

 by the unbarred crissum of the adult plumage. Pelzeln is right in 

 considering it the true M. concentricus. 



PROCEEDINGS B. S. N. H. — VOL. XVI. 6 DECEMBER, 1873. 



