Mr. Gibson gives the following details as to its nesting-habits:--"_Podiceps rollandi_ nests during the latter half of September and beginning of October. The nest is a slight construction of water-weeds, floating on the surface of the water, and only kept stationary by the surrounding rushes. Like _P. major_, it covers the eggs before leaving them. Five is the largest clutch of eggs I have taken; they are originally of a bluish-white colour, but after some time become covered with a brown incrustation of a chalky nature. The average measurement is 1-30/40 × 1-9/40; but there is a variation of 11/40 in length and 7/40 in breadth between my largest and smallest specimens." Specimens of this Grebe were obtained near Cordova by White in 1882. 422. TACHYBAPTES DOMINICUS (Linn.). (AMERICAN DABCHICK.) +Podiceps dominicus+, _Burm. La-Plata Reise_, ii. p. 521 (Pampas); _Baird, Brew., et Ridgw. Water-B. N. A._ ii. p. 438. +Tachybaptes dominicus+, _Scl. et Salv. Nomencl._ p. 150; _Durnford, Ibis_, 1877, p. 203 (Buenos Ayres), et 1878, p. 405 (Centr. Patagonia); _White, P. Z. S._ 1882, p. 629 (Buenos Ayres); _Withington, Ibis_, 1888, p. 473 (Lomas de Zamora). +Sylbeocyclus dominicus+, _Scl. et Salv. Ex. Orn._ p. 190. _Description._--Above dark brown, with blackish mottlings; wings grey, inner secondaries and under wing-coverts white: beneath pale whitish cinereous, chin and throat pure white; neck in front brownish; bill plumbeous, at base yellowish; feet black: whole length 10·0 inches, wing 4·0, tail 1·0. _Female_ similar, but not so bright. _Hab._ Central and South America. This representative of the well-known "Dabchick" of Europe is found throughout South and Central America. In the Argentine Republic, near Buenos Ayres, it is "resident and common in the lagoons and arroyos" (Durnford, _l. s. c._), and likewise in the Territory of Chupat. 423. PODILYMBUS PODICEPS (Linn.). (THICK-BILLED GREBE.) +Podilymbus podiceps+, _Baird, Brew., et Ridgw. Water-B. N. A._ ii. p. 440; _Withington, Ibis_, 1888, p. 473. _Description._--Above dirty brown, varied with blackish; wings cinereous with white tips to some of the secondaries: beneath white, sprinkled with greyish on the breast and sides; chin and throat black; bill short, compressed, plumbeous, crossed by a black band; feet black: whole length 12·0 inches, wing 5·0, tail 1·0. _Female_ similar. _Hab._ North and South America. The Thick-billed Grebe extends all through America, from Canada down to Patagonia and Chili. It does not seem to have been noticed in the Argentine Republic except by Mr. Withington, who sends us a single specimen from the Lomas de Zamora, near Buenos Ayres. A second and larger species of this genus (_P. antarcticus_) occurs on the western side of America from Guatemala to Chili. Order XVIII. IMPENNES. Fam. LII. APTENODYTIDÆ, or PENGUINS.