336 PROCEEDINGS OF THE NATIONAL MUSEUM vol.93 



rather shy. They seemed to be more common on San Martin than on 

 the neighboring peak of Tuxtla. 



This is one of the most remarkable of the discoveries that have 

 come from the careful exploration of the Sierra de Tuxtla and one 

 that offers an especially interesting problem for consideration in con- 

 nection with Dr. Chapman's detailed and enlightening study of the 

 characters of this group written 20 years ago. 78 



Briefly, Atlapetes brunnei-nucha brunnei-nucha has an extended 

 range in the subtropical zone from central Veracruz south through 

 mountainous areas to southern Peru (with a closely allied subspecies 

 xanthogenys in the mountains from Caracas to Merida in Venezuela). 

 The birds from the sections just outlined are marked by a distinct 

 black band across the breast. In the subtropical zone of western 

 Ecuador, in the mountains drained by the Chimbo and Chanchan 

 Rivers, there is found a closely allied form, Atlapetes inornatus, 

 without the black breast band but on the dorsal surface closely similar 

 to the ordinary type. And now in southeastern Veracruz we have 

 Atlapetes apertus, quite like brunnei-nucha above but also lacking 

 the black band across the breast. We have then a widely ranging 

 group of birds, living under definitely restricted zonal conditions, 

 with plain-breasted representatives in isolated areas near either end 

 of the vast range in which the band-breasted type is encountered. 



The three forms are generally similar in pattern and style of 

 coloration, being marked by a combination of brown and black in 

 the crown. They differ, however, appreciably from one another as 

 the following will indicate : 



Atlapetes brunnei-nucha (Lafresnaye) : A black band across the 

 chest, brown of pileum extending back on to the hindneck, bordered 

 laterally by a line of golden brown. (The subspecies xanthogenys 

 differs from the typical form only by having a longer, more slender 

 bill, and a whiter under surface.) 



Atlapetes inornatus (Sclater and Salvin) : Breast without a black 

 band, under surface more extensively white ; brown of crown extend- 

 ing back only to back of head, not reaching the hind neck (but bor- 

 dered as in brunnei-nucha by a line of golden-brown) . 



Atlapetes apertus Wetmore : Breast without black band, brown of 

 pileum extending to hindneck with no lateral line of golden-brown. 



From this it may be supposed that in inornatus and apertus we 

 have the descendents of an ancient species from which the band- 

 breasted brunnei-nucha has evolved and become dominant to spread 

 until it has swamped out the parent stock. Of this parent stock we 

 find now two isolated remnants, one in Veracruz and one in Ecuador. 

 Dr. Chapman has suggested the interesting possibility of an origin 



78 Chapman, F. M., Mutation among birds in the genus Buarremon. Bull. Amer. Mus. 

 Nat. Hist, vol. 48, Oct. 15, 1923, pp. 243-278, figs. 1-3, pis. 14-17. 



