OCR Text |
Show 780 MR. C W. ANDREWS ON A NEW BIRD [June 20, The general aspect of this skull at once gives the impression that it belonged to a Steganopodous bird, and the details of its structure confirm this view: for instance, the extreme posterior situation of the quadrate and the form and position of its orbital process are very characteristic of this group. Comparison of this skull with those of other Steganopodes shows that it is sharply distinguished from the skulls of Phalacrocorax and Plotus in several points. Thus in these genera-(1) the temporal fossa is much larger and its form and relations are different; (2) the form of the occipital region is different; (3) the cranial region is greatly elongated, so that the small orbital process of the quadrate is separated from the orbit by a considerable interval; (4) the roof of the skull behind the rostral hinge is not inflated; (5) the interorbital septum is ossified to a much smaller extent. Tbe skull of Sula differs from the fossil in the following points :-• (1) the temporal fossae are larger; (2) the quadrate is situated somewhat less posteriorly; (3) the roof of the skull is not inflated behind the rostral hinge; (4) in the adult the nostril is reduced to a minute foramen. There is some similarity between the two birds in the form of the occipital surface, the degree of ossification of the interorbital septum, and in the presence of a deep temporalis recess. Apart from the large size and peculiar form of the beak, the skull of Pelecanus differs from the fossil in (1) large size of orbital process of the quadrate; (2) the absence of inflated surface behind the rostral hinge ; (3) the complete ossification of the interorbital septum; (4) the absence of a temporalis recess. The skull of Fregata differs in (1) the rather larger temporal fossa; (2) the much more complete interorbital septum ; (3) large size of orbital process of quadrate ; (4) absence of rostral hinge; (5) the depressed form of the posterior portion of the beak and in the small size of the nostrils. It is to the skull of Phaeihon that the fossil approaches most nearly. Thus the form oi the foramen magnum and the occipital surface, tbe structure and relations of the quadrate (as far as can be determined), the form of the cranial region of the skull, the inflation of the anterior portion of tbe roof immedi-itely behind the rostral binge, are exactly similar in the two forms. Other points of likeness are to be found in the presence of a temporalis recess and the form of the interorbital septum. The chief points of difference are :-(1) in Phaeihon the temporal fossae are slightly larger; (2) the skull-roof in front of orbits is rather wider; (3) the beak is relatively shorter and the nostrils smaller. As to this latter point, however, it is worthy of note that, as Pycraft has pointed out, in a young skull of Phaeihon the narial openings are very much larger than in the adult, and extend back nearly to the rostral hinge as narrow clefts, so that the holorhinal nares of the adult appear as nearly schizorhinal in the young. I have further observed that in some cases, at least, in the adult, traces of the cleft-like posterior portion of the openings remain |