“First, then, with respect to its western limit. This species was discovered by Dr. Gambel, ‘on the eastern side of the Californian range of mountains, in 1841.’ He did not meet with it on the western side; nor has it, as far as made known, been found there since that time by others. During the last summer, search was made for it by several gentlemen who were interested in the subject, as well as by myself, in different localities from north to south along the Pacific slope, but in every instance without success. Hence, the inference must be that this Partridge has never crossed to the west of the Sierra, where, as we well know, it is abundantly replaced by the closely allied species, the ‘_California Partridge_.’ Following down the Sierra Nevada to its junction with the coast-range, you come upon a desert of sand of vast extent; and as the snowy peaks of the Sierra had stopped the march of this species above, so did the burning sands of the desert stop its progress below, and effectually shut it out from the Pacific plain. It is true I found it at _Alamo macho_ (cottonwood grove), which is 44 miles west of the Colorado river. Thus far it had penetrated into the dreary waste, and had managed to find shelter and subsistence where there is little to support animal life. But from this _oasis_ to _Valle-cita_ (little valley), it is seventy miles. In this interval, a vast ocean of sand presents a formidable barrier, as is but too plainly indicated by the bleached bones of horses and mules scattered along the route—and this barrier effectually separates the two congenerous species of partridge: the range of _Gambel’s Partridge_ being confined to the east of this desert, while the range of the _California Partridge_ is confined to the west of it—although on both sides they approach to the very edge, as I ascertained from personal observation. “In the second place, with respect to its eastern limit—I have to repeat that I did not meet with this species in Texas, either in going or returning, anywhere east of the Pecos river; nor was it found by either of three other parties who explored those regions, both previously and subsequently, until after they had passed to the west of that river. Here, again, a sandy desert, between the Pecos and Devil’s river, is the barrier beyond which the species under consideration has not extended its range to the eastward; and, as it is replaced beyond the Sierra and the desert in the west by the _California Partridge_, so is it replaced beyond the Pecos in the east by the _Massena Partridge_.