A very characteristic distinction between _leucurus_ and _axillaris_ is seen in the coloration of the inner webs of the secondaries: in the former, they are abruptly lighter than the outer webs, often pure white, in very striking contrast to the deep ash of the outer surface; in the latter, both webs are of about the same shade of ash, which is much paler than in the other race. Occasional specimens of _leucurus_ occur, however, in which there is little difference in tint between the two webs. LIST OF SPECIMENS EXAMINED. National Museum, 10; Philadelphia Academy, 2; New York Museum, 2; Boston Society, 4; Cambridge Museum, 2; Cab. G. N. Lawrence, 2; Coll. R. Ridgway, 2. Total, 24. _Measurements._ +----+-----------+-----------+---------+---------+-----------+----------+ |Sex.| Wing. | Tail. | Culmen. | Tarsus. |Middle Toe.|Specimens.| +----+-----------+-----------+---------+---------+-----------+----------+ | ♂ |11.80–12.50| 7.30–7.60| .66–.80|1.30–1.50| 1.00–1.15| 8 | +----+-----------+-----------+---------+---------+-----------+----------+ | ♀ |11.60–12.65| 7.20–7.80| .70–.72|1.25–1.40| 1.10–1.20| 8 | +----+-----------+-----------+---------+---------+-----------+----------+ HABITS. The Black-shouldered Hawk is a southern, western, and South American species. On the Pacific it is found to occupy a much more northern range of locality than in the eastern States, where it is not found above South Carolina and Southern Illinois. Specimens have been taken near San Francisco in midwinter. Several individuals of this species, precisely identical with others from the United States, were taken by Lieutenant Gilliss, in the astronomical expedition to Chile. Its range in South America does not appear to be confined, as was supposed, to the western coast, as specimens are recorded by Von Pelzeln as having been obtained by Natterer in Brazil, at Ytarare, Irisanga, and San Joaquin, on the Rio Branco, in August, February, and January. These were taken on the heights. They are also found in the countries of Mexico and Central America. [Illustration: _Elanus leucurus._] This species has been met with in South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas, and probably occurs also in New Mexico and Arizona. Dr. Gambel describes them as very abundant in California, where they are said to be familiar in their habits, and breed in clumps of oaks, in the immediate vicinity of habitations. Dr. Heermann also speaks of them as common in that State. But neither of these naturalists appears to have met with their nests or eggs. It is not mentioned either as a bird of Cuba or Jamaica by Mr. Lembeye, Dr. Gundlach, Mr. Gosse, or Mr. March.