Specimens vary considerably in the shades of color and distribution of the markings, but the types of the above descriptions are the lightest of the series. The darkest example is No. 43,144½ (“♀ and eggs”), Fort Anderson, May 22, 1864. In this the whole head and neck (except underneath) are continuous blackish-plumbeous, only the middle of the auriculars being faintly streaked; the back is nearly plain dusky, and even on the wings the bars are very obscure and much reduced in width. The rump is plain ashy-blue, the darker bars being nearly obsolete. The longitudinal markings on the pectoral region are enlarged into conspicuous stripes, while on the sides and flanks the transverse bars form heavy spots. The transverse bars on the tibiæ are ashy-blue; those on the crissum clear plumbeous, and regularly transverse. Wing, 15.75; tail, 9.30. Upon comparing this specimen with the figures of a pair of var. _gyrfalco_, by Wolf, in Newton’s Oötheca Wolleyana, I can discover no difference at all; thus it would seem that our bird occasionally closely approaches in tints and markings this race of Continental Europe, of which I have seen only one immature example, and no adults. I cannot agree with Mr. Newton in considering the Gerfalcons of the interior of Arctic America as identical with the Iceland form, though that distinguished ornithologist considers them so in his paper in the Proceedings of the Philadelphia Academy for July, 1871, basing his conclusion upon the specimens from which the above descriptions were taken, which had been sent over to England for comparison. I have never yet seen a specimen of _islandicus_ which could not be distinguished, by the characters given in my synopsis, from these examples, while they can be separated from that race by the characters which Mr. Newton himself gives, in his diagnostic table in the paper above cited, for distinguishing the adults of _islandicus_ and _gyrfalco_. The var. _sacer_ is evidently separable from both _islandicus_ and _gyrfalco_, and about as much related to one as to the other; combining the size and proportions of the former with the colors of the latter, while in the wide amount of individual variation of plumage its lighter extreme approaches one, while its darkest phase approximates as closely to the average plumage of the other. LIST OF SPECIMENS EXAMINED. National Museum, 6. _Measurements._ +----+-----------+-----------+---------+---------+-----------+----------+ |Sex.| Wing. | Tail. | Culmen. | Tarsus. |Middle Toe.|Specimens.| +----+-----------+-----------+---------+---------+-----------+----------+ | ♂ |13.35–14.25| 8.50–9.00| .86–.93|2.15–2.40| 1.80–1.95| 3 | +----+-----------+-----------+---------+---------+-----------+----------+ | ♀ |15.50–16.00|10.00–10.50| 1.00–.00|2.35–2.55| 2.00–2.15| 3 | +----+-----------+-----------+---------+---------+-----------+----------+ Var. labradora, AUDUBON. BLACK GERFALCON.