FORM.—Cere and nostril as in the _M. Leucurus_, but the bill not quite so strong. Feathers on the sides and back of head narrow and rather stiff; those on the shoulders obtusely pointed,—which character of plumage is very general in this sub-family. Wing: fourth primary very little longer than the third or the fifth, which are equal to each other. First primary three inches shorter than the fourth or longest, and more nearly equal to the sixth than to the seventh. Extremity of wing reaching to within about an inch and a half of the tail. Tarsi reticulated, with four large scales at the base: upper part covered with plumose feathers for about three quarters of an inch below the knee; but these feathers hang down and cover nearly half of the leg. Middle toe with fifteen scales, outer ones with about nine. Claws of nearly the same degree of strength, curvature and breadth as in _Polyborus Brasiliensis_, or in _M. leucurus_, but sharper than those of the latter. Inch. Total length 20½ Tail 9 Wings when folded 15¾ From tip of beak to anterior edge of eye ⁹⁄₁₀ Tarsus from soles of feet to knee joint 3½ Hind claw measured in straight line from tip to root ⁸⁄₁₀ Claw of middle toe, a twentieth less than that of the hind one. Habitat, Santa Cruz, 50° S. Patagonia. (_April._)