° 1915 J Chapman, The Genus Scytalopus Gould. 421 



taken on Mt. Tacarcuna at altitudes from approximately 3,600 to 

 4,600 ft. 



In the Subtropical Zone of the mountains of western Panama 

 and Costa Rica, Scytalopus panamensis is obviously represented 

 by the nearly related S. argentifrons and the discovery of this new 

 form, makes less inexplicable the occurrence of a species of this 

 genus in a region so far removed from the nearest point at which 

 other species were known to occur. The bearing of this discovery 

 on the faunal affinity of the Subtropical Zones of Costa Rica and 

 western Panama with those of eastern Panama and Colombia is 

 obvious but the subject is too wide to be discussed in this con- 

 nection. 



Specimens examined. — Mt. Tacarcuna, eastern Panama, 10. 



Scytalopus argentifrons Ridgw. 



Scytalopus argentifrons Ridgw., Pr. U. S. N. M. xiv., 1891, p. 475 (Volcan 

 de Range-Irazu, Costa Rica). 



This, the most northern species of the genus, is clearly a repre- 

 sentative form of S. panamensis from which it is now specifically 

 distinct. It is confined chiefly to the Subtropical Zone in Costa 

 Rica and western Panama, ranging in the first-named country, 

 according to Carriker, from 4,000 ft. to timber line, and in western 

 Panama Bangs records it from 5,000 to 7,000 ft. 



Specimens from Boquete and Mt. Chiriqui, when compared with 

 those from Irazu show, in their larger bill and somewhat less 

 silvery forehead, a slight but unmistakable approach toward 

 panamensis. This variation is obvious enough in comparison of 

 specimens but it is too slight to be defined by words or in figures. 



The female of argentifrons apparently lacks the silvery front and 

 superciliaries which distinguish the male and thus closely resembles 

 the female of S. micropterus, a fact which indicates its descent 

 from that species. The female of panamensis on the other hand, 

 possesses (though in a somewhat less conspicuous form) the white 

 superciliaries of the male, and thus bears less resemblance to the- 

 female of micropterus than does the female of argentifrons, though, 

 geographically nearer to it. 



