This species is most nearly allied to _C. brunneicapillus_; the most apparent difference at first sight being in the greater concentration of black on the throat and jugulum in _brunneicapillus_, and the much smaller size of the remaining spots on the under parts, with the decided light-cinnamon of the posterior portion of the body. The outer and central tail-feathers alone are marked as in _C. affinis_, the intermediate ones being entirely black, with the exception of a white subterminal band. This is one of the most characteristic birds constituting the isolated fauna of Cape St. Lucas. Like nearly all the species peculiar to this remarkable locality, it is exceedingly abundant, breeding in immense numbers. It has not yet been detected elsewhere, though it may possibly be found on the Lower Colorado. HABITS. This recently described species was first discovered by Mr. Xantus, and has, so far as is known, a somewhat restricted locality, having been met with only at the southern extremity of Lower California, where it is an exceedingly abundant bird. Mr. Xantus has published no observations in regard to its habits, which, however, are probably very nearly identical with those of the more common species. From the brief memoranda given by him in the general register of his collections, made at Cape St. Lucas, we gather that their nests were built almost exclusively in opuntias, cacti, and the prickly pear, and were generally only four or five feet from the ground, but occasionally at the height of ten feet. The nests are large purse-shaped collections of twigs and coarse grasses, very similar to, and hardly distinguishable in any respect from, those of the more northern species. The eggs vary from 1.05 to 1 inch in length, and from .65 to .70 of an inch in breadth, and have a reddish-white ground very uniformly dotted with fine markings of reddish-brown, purple, and slate. SUBGENUS SALPINCTES, CABANIS. _Salpinctes_, CABANIS, Wiegmann’s Archiv, 1847, I, 323. (Type, _Troglodytes obsoletus_, SAY.) GEN. CHAR. Bill as long as the head; all the outlines nearly straight to the tip, then decurved; nostrils oval. Feet weak; tarsi decidedly longer than the middle toe; outer lateral toe much longer, reaching to the base of the middle claw, and equal to the hinder. Wings about one fifth longer than the tail; the exposed portion of the first primary about half that of the second, and two fifths that of the fourth and fifth. Tail-feathers very broad, plane, nearly even or slightly rounded; the lateral moderately graduated. Of this genus but one species is so far known in the United States, the Rock Wren of the earlier ornithologists. It is peculiar among its cognate genera by having the two continuous plates on each side the tarsus divided into seven or more smaller plates, with a naked interval between them and the anterior scutellæ. Other characters will be found detailed in the Review of American Birds, p. 109. Salpinctes obsoletus, CABAN.