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Show 1889.] MR. W. K. PARKER ON STEATORNIS CARtPENSlS. 177 the 13th sacral is identified as such by its close union (ankylosis) with the postero-superior angles of the post-ilia ; its centrum is distinct from that of the 12th. Here, in this manifestly archaic bird we have, as in the Parrot tribe, a marvellous variety in the articulations and functions of the vertebral centra. The atlas is procoelous, and its joint, behind, with the axis, is flat, with a joint-cavity. The joint-cavity, with a perforated meniscus and a suspensory ligament, is seen up to the sacrum ; but the cervicals, only, are cylindroidal; the dorsals are opisthoccelous. Then the sacrals are ankylosed, and behind these come the caudals; which, in front, are subconcave on both faces, and are united by fibro-tartilage without a joint-cavity; whilst in the hinder part of the series that cavity reappears in a procoelous joint. IV. The Sternum and Shoulder-girdle. The sternum (Plate XVIII. figs. 7, 8) belongs to the same type as that of Caprimulgus on the one hand, and Buceros on the other, but is most like that of the latter. Like the pelvis it is short and broad, and it has only two notches; they are wide and rounded, and the xiphoids are all three finished behind by a large rounded plate of cartilage. The whole structure is light and rather feeble, and the bone is pneumatic. The coracoid grooves nearly meet; they form together little more than a right angle ; between them there is a short, blunt, inferior rostrum (r.st.), scooped above and carinate below. Together, the ^re-costal process (pep.) and the costal edge form a high, nearly equilateral triangle; there are four transverse condyles for the sternal ribs; the first of these only leaves a pre-costal tract 3*5 millim. in extent. The body of the bone is deep and the keel large, with its fore margin at a right angle with the body; in front, the keel projects a little at its lower third, where the lesser pectoral muscle ends behind; it ends 4 millim. in front of the ossified part, and about 13 millim. from the end of the middle metasternal cartilage (middle xiphoid). The whole structure, shoulder-girdle and sternum, is much like that of the Barn-Owl (Strix flammea), with its single notch right and left behind, the inner notches being nearly obsolete; that bird also has similar long scapulae and coracoids, and the furcula are not unlike. This peculiar isomorphism with the Owl is manifestly adaptive; I question if this bird is nearer akin to an Owl than it is to a Cormorant. The structure of the sternum is in great contrast to that of the Common Goatsucker; in respect of its general finish it is more archaic. The comparative measurements are as follows:- Axial Breadth Breadth Length Depth length. in front. behind. of keel. of keel. millim. millim. millim. millim. millim. Caprimulgus.. 27 16 25 32 12 Steatornis . . 5 8 43 52 45 18 The notches in Steatornis measure 9 millim. axially and 15 |