Long. tot. 4¹⁄₁₂ unc; _alæ_, 2³⁄₁₂; _caudæ_, 1⁹⁄₁₂; _tarsi_, ⁷⁄₁₂; _rost._ Forehead, stripe over the eye, and all the under surface pale buff; back of the neck and upper surface chocolate brown; greater and lesser wing coverts margined with buff. Habitat, Galapagos Archipelago, (_September_). From the appearance of this bird when alive, although closely resembling _P. nanus_, I entertained no doubt that it was a distinct species. Mr. G. R. Gray informs me that there is a specimen of a male in the British Museum, which differs from the male of the precedent species, in having the upper colour of a decided brown, and the external margins of the outer tail feathers and tips of the secondaries rather reddish white; also in size as stated by Mr. Gould. MYIOBIUS. _G. R. Gray._ TYRANNULA. _Swains._ Mr. Gould had adopted for the following species Mr. Swainson’s generic appellation of _Tyrannula_, but Mr. G. R. Gray has pointed out, that as Tyrannulus was proposed and published eleven years before, namely in 1816, by Vieillot, it becomes necessary to change the former name, and therefore he proposes _Myiobius_. 1. MYIOBIUS ALBICEPS. _G. R. Gray._ Muscipeta albiceps. _D’Orb. & Lafr._ Mag. de Zool. 1837, p. 47. This bird is not uncommon in Tierra del Fuego, and along the western coast of the southern part of the continent, where the land is covered with trees; it is occasionally found near Valparaiso in central Chile; and likewise in Banda Oriental on the banks of the Plata, where the country is open, from all of which places I procured specimens. At Port Famine and in the islands of the Chonos Archipelago, it inhabits the gloomiest recesses of the great forests. It generally remains quietly seated high up amongst the tallest trees, whence it constantly repeats a very plaintive, gentle whistle, in an uniform tone. The sound can be heard at some distance, yet it is difficult to perceive from which quarter it proceeds, and from how far off; and I remained in consequence, for some time in doubt, from what bird it proceeded. 2. MYIOBIUS AURICEPS. Tyrannula auriceps. _Gould_, MS. _M. rufus; capite cristato nitidè flavo; plumarum apicibus brunneis; alis brunneis, secundariarum marginibus tectricumque apicibus rufis; caudâ pallidè brunnea, plumarum externarum marginibus externis pallidioribus; gutture corporeque subtus pallidè flavescenti-albis; plumis singulis fasciâ centrali brunnea._ Long. tot. 5³⁄₁₂ unc; _alæ_, 2⁵⁄₁₂; _caudæ_, 2⁶⁄₁₂; _tarsi_, ⁹⁄₁₂; _rost._ ⁷⁄₁₂.