1 6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



del Toro, and the forms with the anterior under surface barred closely 

 with black and white that range from eastern Darien through western 

 Colombia to Ecuador, long led to their separation under two specific 

 names. The series of specimens now available justifies their union 

 under the specific name nigricapillus, though it may be supposed that 

 the two terminal groups must have been separated for a long period 

 to have become so completely different. In costaricensis, the darkest 

 of the Central American races, and the one farthest removed from 

 those of South America, remote common ancestry with the other is 

 indicated in the rather indistinct black bars found on the breast and 

 sides in the juvenile plumage. This marking may persist in the fol- 

 lowing plumage, especially on the abdomen, but many are plain chest- 

 nut on the posterior lower surface except for the bars on the lower tail 

 coverts that are common to many of the numerous species of the 

 genus Thryothorus. Proceeding eastward along the Caribbean coast 

 of Panama from the valley of the Rio Calovevora, on the boundary 

 between the provinces of Bocas del Toro and Veraguas, the wrens of 

 the species under discussion become paler brown, with sides and flanks 

 barred with black, except for occasional plain individuals. This group 

 — the race castaneus — is found through the lowland Caribbean drain- 

 age of the Canal Zone. 



Continuing eastward there is an abrupt change near Portobello 

 and in the foothills of the Cerro Azul in which the plain white of the 

 throat extends down on the upper breast, the brown on the sides 

 becomes paler, and there are strongly marked black bars on sides, 

 lower breast, and abdomen in most individuals. This style — the race 

 reditus — crosses to the Pacific slope along the base of the Cerro Azul, 

 and at Chiman has reached the coastal lowlands. On the Caribbean 

 slope it continues almost to the Colombian boundary in the Comarca 

 de San Bias, and on the Pacific side to about the western boundary of 

 Darien near the Golfo de San Miguel. There is then rather abrupt 

 transition to birds with lower surface heavily barred — the race 

 schottii. Markings on the white throat are faint or absent, and the 

 brown is restricted to the flanks and under tail coverts. In the valley 

 of the Atrato the barring reaches its maximum and here the throat 

 in most specimens is heavily marked. The plainer throat persists to 

 the eastward in Colombia along the Rio Sinu, and on the middle and 

 upper Rio Cauca. In southwestern Colombia, beginning in the Depart- 

 ment of Cauca, the throat bars begin to lighten still more and to 

 disappear, and farther south, in Narifio, the upper breast also becomes 

 less heavily marked. This style leads over to typical nigricapillus of 

 Ecuador, in which throat and upper breast are white, without bars, and 



