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Show 1899.] FROcM THE LONDON CLAY OF SHEPPEY. 781 as one or two minute foramina, marking paints where the closure of the cleft is incomplete. Probably in the early ancestors of Phaeihon the nares were schizorhinal, and in Prophaethon they still approximate to that condition. It must be pointed out that in the Steganopodes generally there seems to be a strong tendency to the reduction in size of the external nares, and in Sulci this has been carried so far that the opening is reduced to a very small foramen ; and it is remarkable that in Odontopteryx1, which was a contemporary of Prophaethon, this condition seems to have been already attained, so that in this respect this Eocene type is more specialized than the recent Phaeihon. So far as the evidence of the skull goes, it may be concluded that Prophaethon approaches very nearly to Phaeihon, of which it is probably an ancestral form, exhibiting in a few points more primitive characters. The dimensions of the skull and mandible are :- millim. Total length from oce. condyle (tip of beak wanting) .. 112 Width at squamosal prominence (approx.) 40 Width at temporal fossae 26 Width at postorbital process 46 Width between orbits 17 Width at rostral hinge 16 Width of beak opposite anterior angle of antorbital vacuity 16 Diameter of foramen magnum 8 Length from occipital condyle to rostral hinge in straight line 51 The Pelvis. (See Plate LI. and text-figure 2, p. 782.) By the careful removal of the matrix a great part of the pelvis is now exposed, but it is incomplete posteriorly and the right side of the preacetabular portion is still concealed. In the preacetabular region the ilia are united along the middle line with the neural spines of the sacral vertebrae to form a broad low iliac crest. Their lateral (gluteal) surfaces are very concave, and they seem to have beeu widened out anteriorly as in the pelves of Phalacrocorax and Plotus. Just in front of the acetabulum the dorsal edges of the ilia diverge one from another and the whole pelvis increases in width, 1 This bird is regarded by most authors as an undoubted Steganopod, but in his original description Owen pointed out some points of resemblance with the Anserine birds. I have lately cleared the matrix from the orbit, quadrate, and pterygoids of the type specimen, and the new characters thus revealed point rather strongly to Anserine affinities: for instance, the term of the pterygoids is extremely duck-like, and they articulate by broad subcircular surfaces, situated at their anterior ends, with corresponding facets near the base of the rostrum ; many of the Steganopod-like characters, however, are of considerable importance. I hope shortly to publish a note on Odontopteryx with figures of the quadrate and pterygoids. |
