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Show 784 ON A NEW' BIRD FROM THE LONDON CLAY. [Jtiue 20, molluscs, or, in the case of the Frigate-bird, on what they can take from the Gannets and other birds. I never saw either really dive, although they drop down to pick up food from the surface of the sea, and on one occasion only I saw a Tropic-bird sitting on tbe water. This being the case, it appears that the hind limbs are scarcely used at all, and the reduction in size that has been undergone by the pelvis and hind limb is no doubt correlated with this disuse. In Prophaethon both pelvis and hind limb seem to have retained their normal relative size, and this bird was probably a good swimmer and diver and resembled Sula and Phalacrocorax both iu its habits and in its structure more nearly than does its modern representative Phaeihon, many of the peculiar characters of which have been acquired since the Eocene. Nevertheless, Phaeihon presents many peculiarities which indicate that it is really a somewhat primitive type, and probably the stock of which Prophaethon and Phaeihon are the middle and terminal members branched off from the common stock of tbe Steganopodes at a very early period, perhaps not later than about the beginning of the Cretaceous. It is known that the group is a very ancient one, for Marsh has described several species (Graculavus) which occur in the Upper Chalk, and were regarded by him as almost certainly Steganopodes which already show relationship with the Cormorants. The dimensions of the pelvis are:- millim. Total length as preserved y8 Width at antitrochanter 27 Width at middle of pelvic escutcheon 15 Length in front of antitrochanter 49 Length of ischiadic foramen 25 The dimensions of the femur are :- millim. Length (approximate) 59 Antero-posterior width of outer surface of trochanter.. 11 Width of middle of shaft 5 CONCLUSIONS. The conclusions arrived at from the examination of this specimen may be summarized as follows :- (1) The structure and position of the quadrate and the form of the pelvis indicate that tbe fossil is a Steganopodous bird. (2) The form of the cranial region of the skull and of the rostral hinge, as well as some other points, indicate that it is most nearly related to Phaeihon. (3) The relatively large size of the pelvis and femur indicate that the bird more nearly resembled the ordinary Steganopodous type than does Phaethon, in which the pelvis and hind limb are in a greatly reduced condition. |