Dr. Heermann represents the nest as composed of fine mosses, lined with the feathery down of various seeds, and containing two white eggs. He saw this bird also at Guaymas, in Mexico. The figures in our plate are of the size of life, and represent adult males. The plant represented is _Odontoglossum Cervantesii_, a native of Mexico. DESCRIPTION AND TECHNICAL OBSERVATIONS. Genus Trochilus. Linnæus, Syst. Nat., I. p. 189. (1766.) Size small, in some species diminutive, and the smallest of birds; bill slender, frequently straight, and also frequently curved, acute; wings comparatively large, generally pointed and formed for rapid flight; quills flattened, first primary longest, and curved inwards; tail various; legs and feet very short and feeble. The birds of this group are exclusively American. Trochilus Alexandri. Bourcier and Mulsant, Annals of the Royal Society of Physical and Natural Sciences of Lyons, IX. p. 330. (1846.) Form. Small; bill long; nearly straight; wings rather short; first quill longest, and somewhat curved; tail rather short, marginated, with its feathers narrow and pointed; legs and feet very short and weak. Dimensions. Total length of skin, about 3¼ inches; wing, 2¹/₁₀; tail, 1 inch. Color. Entire upper parts golden green; dark on the head; wings and tail brownish-black, except the central feathers of the latter, which are green; throat brilliant purple, with violet reflections, which color is succeeded by a broad transverse band of white; other under parts golden green, mixed with pale brownish and ashy; bill and feet dark. Hab. California and Mexico. Spec. in Mus. Acad., Philada. Obs. This bird is about the size of, or slightly larger than the ruby-throated Humming Bird (_T. colubris_) of North America, and resembles it in the general distribution of its colors. Those of the throat are, however, entirely different. The two species belong evidently to the same subdivision of the old genus _Trochilus_, which is, however, given so differently by late authors, that we have not at present determined the relative claims of either. It is given by one as belonging to the genus _Mellisuga_, and by another as _Trochilus_ proper, in a restricted sense. The study of the Humming Birds, now difficult, will be rendered easy by Mr. Gould’s great work on these birds, now in the course of publication. All the known species are to be figured of the size of life; and in the parts already published, the drawing and coloring is exceedingly accurate, and magnificent beyond any precedent in the literature of ornithology. In the old world, the Humming Birds are represented by the Sun Birds (genus _Cinnyris_, Cuvier; _Nectarinia_ of some authors), numerous species of which inhabit Africa and Southern Asia. They partake in some measure of the habits of the Humming Birds, and also of their lustrous colors, many of the species being very beautiful.