An egg of the _islandicus_, from Iceland, has the same measurements, but is so slightly yet uniformly marked with light yellowish-brown as to seem to be of one color only,—a light brown, shaded with yellow. An egg from Norway, of the form _gyrfalco_, is 2.42 inches in length, 1.71 in breadth, has a ground-color of a dirty yellowish-white, and is marked with spots, dottings, and confluent blotches of yellowish-brown, more so about the larger end. The series of eggs of _Falco sacer_ in the Smithsonian Collection exhibits the following range of variation in size, color, and markings: length, from 2.30 to 2.45 inches; breadth, 1.60 to 1.90 inches; ground-color usually a light reddish-ochre, varying to pinkish on the one hand, and to rufous on the other. They are usually sprinkled all over with small spots, which are sometimes not distinguishable from the ground-color when this is very deep, and again larger and quite conspicuous. An egg of the variety _candicans_, from Greenland (No. 2,606, S. I.), measures 2.25 inches by 1.80. In color and in markings it is like the average eggs of variety _sacer_, namely, pale rufous, sprinkled over with a slightly deeper shade. Falco lanarius. Var. =polyagrus=, CASSIN. AMERICAN LANNER; PRAIRIE FALCON. _Falco polyagrus_, CASSIN, B. Cal. & Tex. 1853, 88.—IB. P. A. N. S. 1855, 277; B. N. Am. 1858, 12.—HEERM. Pacific R. Rep’t, II, 1855, 31.—KENNERLY, P. R. R. III, 1856, 19.—COOP. & SUCKL. P. R. R. XII, 1860, 143.—COUES, P. A. N. S. 1866, 7.—STRICKL. Orn. Syn. I, 1855, 85.—DRESSER, Ibis, 1865, 323.—GRAY, Hand List, I, 1869, 20. _Falco lanarius_, var. _mexicanus_, RIDGWAY in COUES’ Key, 1872.