The var. _mexicanus_ and var. _jugger_, which are both much darker, and more uniform in the coloring of the upper parts, than var. _polyagrus_, are more nearly alike; in fact, the only tangible difference that I can find between a specimen of the former in the Museum of the Boston Society of Natural History (No. 1,438, ♂, Juv. Lafr. Collection; “Mexico”) and two examples of the latter in the New York Museum, consist in the larger size of the var. _jugger_ (see synopsis), besides its whiter cheeks and more isolated and distinct “mustache.” A direct comparison of these two races may show other tangible points of distinction, or, on the contrary, may show even these slight distinguishing features to be inconstant. The former result is, however, most reasonably to be expected. LIST OF SPECIMENS EXAMINED. National Museum, 9; Boston Society, 2; Philadelphia Academy, 4; Museum Comp. Zoöl. 1; G. N. Lawrence, 2; R. Ridgway, 5. Total, 23. _Measurements._ +----+-----------+-----------+---------+---------+-----------+----------+ |Sex.| Wing. | Tail. | Culmen. | Tarsus. |Middle Toe.|Specimens.| +----+-----------+-----------+---------+---------+-----------+----------+ | ♂ |12.00–00.00| 7.60–0.00| .00–.75| .00–2.15| .00–1.70| 6 | +----+-----------+-----------+---------+---------+-----------+----------+ | ♀ |13.25–14.25| 8.00–9.00| .85–.90|2.05–2.40| 1.85–2.00| 12 | +----+-----------+-----------+---------+---------+-----------+----------+ HABITS. This is an exclusively western species, occurring from the valley of the Mississippi to the Pacific coast. Specimens have been obtained as far east as Illinois. Several others have been taken on the Upper Missouri and the Yellowstone Rivers, in Nebraska, at Fort Thorne, New Mexico, and on the Little Colorado River. A specimen was shot by Dr. Heermann on the Farallones, on the California coast; but Dr. Cooper thinks it rarely visits the coast border, though he several times saw, near San Diego, a bird which he supposed to belong to this species. At Martinez, in December, 1863, he succeeded in shooting one as it flew from its perch at the approach of the wagon in which he was riding. It is said to extend its migrations in summer to the Upper Columbia, avoiding the densely forest-clad regions. Dr. Heermann saw a young unfledged individual at San Francisco, from which it may be inferred that a few may breed within the State. The first individual of this species was taken by Dr. Townsend during his trip across the continent, in 1834. It was obtained among the mountainous regions of Oregon, near the sources of the Platte River. Mr. Cassin states that Dr. Heermann procured several specimens in the Sacramento Valley. Mr. Cassin remarks that this species, except in its greatly superior size and strength, bears a very close resemblance to the well-known Jugger Falcon of India, a bird much used for the purposes of falconry.