314 Annals of the Carnegie Museum. 



While this settlement of the case disposes conclusively of the dif- 

 ficulties encountered by Mr. Ridgway in attempting to include Colom- 

 bian specimens under atrinucha, it raises another question in dis- 

 tribution not so readily settled. Dr. Chapman has shown that in 

 western Colombia atrinucha is the form which occurs, ranging over 

 to the Magdalena Valley. If, therefore, the birds from Gorgona Is- 

 land, lying off the west coast of Colombia, and the Santa Marta region 

 are to be considered the same — and there are certainly no sufficient 

 grounds for their separation in the judgment of the writer — we are 

 confronted by a most peculiar case of discontinuous distribution. The 

 only explanation that seems pertinent is that this is a case of parallel 

 development under similar environmental conditions. 



This ant-shrike is strictly a Tropical Zone form, being found 

 throughout the lowlands and semi-arid foothills up to 3,000 feet, but 

 not regularly above 1,500 feet. It is most abundant in the forest of 

 the lowlands at Don Diego on the north coast and about Fundacion 

 and Tucurinca to the southwest, but has been detected also at Valencia 

 and Loma Larga, on the other side of the mountains. It is partial to 

 dense thickets and masses of vines, is very tame, and is always found 

 in pairs. 



265. Thamnophilus nigriceps Sclater. 



Twenty-seven specimens: Tucurinca, Tierra Nueva, Trojas de 

 Cataca, and Fundacion. 



This species was described by Sclater in 1869 (Proceedings Zoolog- 

 ical Society of London, "1868," 1869, 571) from a single unsexed 

 " Bogota " skin. Just about the same time Lawrence described a bird 

 from Turbo, Colombia (Proceedings Academy of Natural Sciences 

 of Philadelphia, '"1868," 1869, 361), under the name Thamnophilus 

 virgatus, which appears to be the same thing, or at least conspecific. 

 There are a number of females in the present series, which correspond 

 fairly well to Sclater's original description and later figure (Catalogue 

 of the Birds in the British Museum, XV, 1890, pi. 12), except that the 

 streaking on the pileum and under parts is much broader. The im- 

 mature male appears to be very similar to the adult female, but the 

 adult male is an entirely different looking bird, being black above and 

 below, the flanks more or less tinged with slaty gray, and the outer 

 greater under wing-coverts and the inner margins of most of the 



