Prof. Owen has figured the shaft of a fine example of this bone in Dixon's Geology of Sussex, Pl. XXXIX. fig. 11. A good proximal end is shown in Pl. XXXII. fig. 2, of Prof. Owen's monograph of the Cretaceous Reptilia, but the figure appears to have been previously given in Pl. XXIV. fig. 2 of the same monograph. By far the grandest specimens are drawn in Pl. XXX. Prof. Owen names these wing bones. In the "Literature of English Pterodactyles" the loss of the proximal epiphysis from the specimen represented in Prof Owen's fig. 1 and 2 led me to interpret the bone as an ulna. Figs. 1 to 4 represent the proximal ends and greater portions of the shafts of first phalanges. The lower bone in fig. 5 is neither radius nor ulna, as stated in the text of the Cretaceous Reptilia, but the shaft and distal end of a first phalange; the upper bone being the second phalange. The Proximal End. The straight shaft throughout its length is triangular in section. One side of the bone is gently convex; this may be named for convenience the outside. The two parts which make up the other side are inclined, and have the angle in which they meet rounded; one part looks upward and inward, the other downward and inward. Towards the proximal end the bone widens and thickens, and the moiety of the inner side which is away from the heel becomes cleft, and has the sides of the depression rounded to form a large pneumatic foramen. The articular surface looks upward and a little outward on the side of the pneumatic foramen. It consists of two semicircular concave grooves, separated by an intervening low convexity. The outer of these grooves extends from the margin of the extreme proximal point of the heel to the widest point of the bone; the other groove more deeply concave, is a third shorter, extending from inside the pneumatic foramen to the heel. Here both grooves converge, terminating in a point, exterior to which a little distally is a hemispherical mammilate eminence. On the distal side of the eminence there is a depression so as to make the angle behind the heel almost hemispherically rounded. This articulation fits on to the distal articulation of the wing-metacarpal. When the proximal epiphysis forming the heel comes away, it leaves a large sub-circular pit with a depressed narrow border. Distal End.