1809.] FROM THE LON^DON CLAY OF SHEPPET. 781 



as one or two minute foramina, marking puiutss where the closure 

 ol: the cleft is incomplete. Probably in the early ancestors of 

 Phaeihon the nares were achizorhinal, 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 Sula this has been 

 carried so far that the opening is reduced to a very small foramen ; 

 and it is remarkable that in Odontopteryx^, which was a con- 

 temporary oi 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 ma)'^ ho concluded 

 that Prophaethon approaches very nearly ro Phaethon, of which it is 

 probably an ancestral form, exhibiting in a few points more primi- 

 tive characters. 



The dimensions of the skull and mandible are : — 



millim. 

 Total length from occ. condyle (tip of beak wanting) . . 112 



Width at squamosal prominence (approx.) 40 



Width at temporal fossie 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 oi 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 been widened out anteriorly as in the pelves 

 of Phalacrocorax and Ploius. 



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 fcrni of the 

 pterygoids is extremely duck-like, and they articulate by broad subcircular 

 surfaces, situated at their anterior ends, with «orresponding 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 Odoutapteryx 

 with figures of the quadrate and pterygoids. 



