The eggs measure, one 1.81 inches in length by 1.69 in breadth, the other 1.78 by 1.63. This does not materially vary from the measurement given by Darwin. The ground-color of the egg is white. This, however, is so thickly and so generally studded with fine brown markings, that the white ground to the eye has a rusty appearance, and its real hue is hardly distinguishable. Over the entire surface of the egg is distributed an infinite number of fine dottings, of a color most nearly approaching a raw terra-sienna brown. Over this again are larger blotches, lines, and splashes of a handsome shade of vandyke-brown. In one egg these larger markings are much more frequent than in the other. The latter is chiefly marked with the finer rusty dottings, and has a more dingy appearance. SUBGENUS TINNUNCULUS, VIEILLOT. _Tinnunculus_, VIEILL. 1807. (Type, _Falco tinnunculus_, LINN. _Tinnunculus alaudarius_, GMEL.) _? Tichornis_, KAUP, 1844. (Type, _Falco cenchris_, NAUM.) _Pœcilornis_, KAUP, 1844. (Type, _Falco sparverius_, LINN.) The characters of this subgenus have been sufficiently defined in the diagnosis on page 1427, so that it will be necessary for me only to add a few less important ones. [Illustration: =53198=, ♀. =53198=, ♀. ½ =53198=, ♀. =53198=, ♀. ½ _Tinnunculus sparverius._] The subgenus _Tinnunculus_ is one which is well characterized by peculiarities of manners and habits as well as by features of structure. The species are the most arboreal of the Falcons, and their curious habit of poising in a fixed position as they hover over some object of food which they are watching is probably peculiar to them, and has been remarked of the Old World as well as of the American species. In their structure they are the most aberrant members of the subfamily belonging to the Northern Hemisphere and in their weak bill and feet, lengthened tarsi, obtusely tipped quills, more rounded wings, and more lengthened tail, exhibit a decided step toward _Hieracidea_, an Australian genus which is almost exactly intermediate in all the characters of its external structure between the true Falcons and the South American genus _Milvago_, of the Polyborine group. The subgenus is most largely developed in the Old World, where are found about a dozen nominal species, of which perhaps one half must be reduced to the rank of geographical races. America possesses three species, two of which are restricted to the West India islands, while the other extends over the entire continent. There is no reason whatever for separating the American species from those of the Old World, and the subgenus _Pœcilornis_, established upon these by Kaup, is not tenable.