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18 THI? CONDOR Vol. XVII Geographically the two forms appear to be absolutely and widely separ- ated. Between the mountains of the San Diegan district of southern Califor- nia, comprising the habitat of occidentalis, and the mountains of southeastern Arizona, where huachucae occurs, lies a stretch of desert several hundred miles in extent, forming an impassable barrier between the two. The Spotted Owl is a bird of the high Upper Sonoran and Transition zones, and is nowhere known to have occurred at any Lower Sonoran locality. Furthermore, it is restricted associationally, showing marked preference for heavily timbered region?; such places in the habitats of occidentalis and huachucae being almost invariably shady canyons or densely wooded hillsides. Although the Upper' Sonoran zone extends quite continuously from southeastern Ari. zona northward into central Nevada, and then westward into Califo. rnia, and there might be deduced from this a continuity of range of one form with the other, such ar- gument would l?e fallacious, for this region is the .extremely arid Upper Sono- ran of pition and juniper, offering nothing to a bird with the requirements of the Spotted Owl. The species has not so fa? been found in northern Arizona, nor is it. known from the east slope of the Sierras, in California, so that altogether it seems highly probable that there is an extensive hiatus between the regions inhabited by the Spotted Owl in southern Arizona and in southern California. It is to be expected, of course, that segregation amid widely different surroundings, acting upon a non-migratory animal, would be productive of some variation in the inhabitants of the different regions. Furthermore, the observed differ- ences distinguishing the few known specimens of the Arizona race from the California subspecies, are exactly such as we would expect to find, reasoning from analogous cases among other animals of similar distribution. Thus there seems to be ample justification for the recognition of the differences existing between the California and the Arizona races of Strix Occidentalis. As to the relationship of the latter, the Arizona bird, to the form of Spotted Owl occur- ring southward over the table land oF Mexico, that is another matter, to be de- termined by future study of more material than is now available. As stated above, the opportunity I have enjoyed of making the compari- sons herein recorded, is primarily due to the consideration of Dr. Louis B. Bishop, in loaning me his Arizona specimens: Of the other skins examined, the type specimen of S. o. huachucae was borrowed from the California Museum of Vertebrate Zoology, where it is on deposit as part of the 'Morcom collection; while the examples of S. o. occident?lis are all either from the collection of the Los Angeles Museum of History, Science, and Art, or of the several individuals who have their collections on deposit in that institution. Their names appear in the appended list of specimens, and to each one I wish to express my appre- ciation of the privilege I have enjoyed. Accompanying is a list of the specimens upon which this study is based. The examples of S. o. occidentalis are all from points in the San Diegan district, southern California; of S. o. huachucae, from southeastern Arizona. For the sake of the measurements I have included several skins not actually handled at this time. The data pertaining to these is copied from my previous paper on the species, before cited, and these skins, during the preparation of that paper, were carefully compared with the one example of huachucae then available.