BIRDS 277 



to the feathers, below buffy-white spotted with brown on the breast 

 and on the sides. Bill slender; culmen curved, not greater than 

 eighteen millimeters, contained one and one third times in the tarsus; 

 depth of bill about equal to gonys. 



The two species at present known under this subgenus without 

 doubt stand nearer to the ancestral Geospiza than does any other 

 known member of the genus. The plumage of the male and the fe- 

 male is the same and is identical with that of young birds of Cama- 

 rhynchus and Geospiza proper before they have begun to assume the 

 melanistic phase characteristic of all the higher Geospizce. Young 

 birds of this subgenus, in the first plumage, have a bright olivaceous 

 color, a character common to young birds of Cactospiza and Cama- 

 rhynchus but lost by all the members of Geospiza proper and of Cac- 

 tornis. The adults reach the brown-spotted stage attained by the young 

 of the other higher groups in Stage III. Hence, during their life 

 history, the members of Cactospiza go through Stages I, II and III. 



One member of the subgenus, G. heliobates, is an inhabitant exclu- 

 sively of the mangrove swamps of the archipelago. It might be fanci- 

 fully supposed that these mangrove swamps were the first vegetation 

 on the islands and that G. heliobates, or an ancestor of the present 

 Geospizce resembling it, lived in these swamps until the islands became 

 elsewhere fit for habitation ; that then some of the birds left the 

 swamps and became differentiated into the species of Camarhynchus, 

 Geospiza proper, and Cactornis ; while the others, remaining in the 

 swamps, retained their primitive plumage, and survive at present as 

 G. heliobates. The mangrove swamps were, most probably, the first 

 vegetation of the islands on which they occur, but they are not pres- 

 ent to any extent anywhere except on the southeast part of Albemarle, 

 along the shores of the straits between Albemarle and Narboro, and 

 at Elizabeth Bay, Albemarle. These islands do not by any means 

 appear to be the oldest of the archipelago and their mangrove swamps 

 stand on very recent lava. Hence the greater probability is that G. 

 heliobates has been derived from G. pallida, the member of Cacto- 

 spiza that inhabits the same areas as the other Geospizce. The two 

 species differ only in the size of the bill. 



53. GEOSPIZA PALLIDA (Sclater and Salvin). 



Cactornis pallida SCLATER AND SALVIN, Proc. Zool. Soc. Lond., p. 323, 



1870 (Indefatigable Island). 

 Cactornis hypoleuca RIDGWAY, Proc. U. S. Nat. Mus., xn, p. 109, 1890 



(James Island). 

 Camarhynchus pallidus RIDGWAY, Proc. U. S. Nat. Mus., xix, p. 565, 1896; 



Bull. U. S. Nat. Mus., 50, Pt. I, p. 487, 1901. 



Proc. Wash. Acad. Sci., January, 1904. 



