Obs. On comparison of our specimens from Texas with others from various parts of South America, we cannot at present find differences sufficient to induce us to regard them in any other light than as one species. The present is the first bird of its genus which has been observed within the limits of the United States. The sexes of this species are quite unlike each other, the female having none of the brilliant color of her companion. The figures in our plate represent the adult and young males about two-thirds of the natural size. [Illustration: Plate 19 The Blue Partridge Callipepla squamata (_Vigors_)] CALLIPEPLA SQUAMATA.—(Vigors.) The Blue Partridge. The Scaly Partridge. PLATE XIX.—Male and Female. This is another of the fine game birds that inhabit the countries on the southwestern frontier of the United States, and the adjoining regions of Mexico. Though not presenting such gay colors in its plumage as the two other Partridges which we have previously figured in the present work, it is by no means destitute of claim to respect in personal appearance, and in gracefulness and delicacy of form is not at all their inferior. We have always particularly admired its ample and curious crest, which is possessed by both male and female, and, though admitting of being flattened so as to lie close on the head, is usually to be seen erect, and gives it an air unusually spirited and striking. It is remarkable for great swiftness in running, and is more of an insect-eater than is usual in this family of birds. It is abundant in Texas and New Mexico. Specimens of this bird had reached Europe as early as 1830, in which year it was first brought to the notice of naturalists by Mr. Vigors, one of the founders of the Zoological Society of London, and one of the most profound naturalists of the only school of systematic Zoology, the Circularian and Quinarian, which Anglo-Saxon mind has yet produced, a consideration one would think not slightly to be regarded. His description is in the Zoological Journal, V. p. 275. It has, however, always, until within a few years, been of great rarity in collections, and nothing was known of its history or habits until the publication of the valuable contributions to Natural History which have been made by officers of the Army of the United States.