402 Mr. R. Lydekker on 



of the large pneumatic foramen which is so conspicuous ou 

 the anterior surface of the proximal extremity of the latter. 

 In this respect the fossil agrees with the ulna of the Cormo- 

 rants {Phalacrocoraoc), although it differs in other points. 



One other specimen which has been referred to Argillornis 

 must not be passed over without special mention. This spe- 

 cimen is an imperfect cranium from Sheppey, now in the 

 British Museum, which was described and figured by Sir R. 

 Owen in the 36th volume of the ' Quart. Journ. Geol. Soc* 

 From its somewhat small relative size as compared with the 

 type humeri, this specimen may have belonged to a female 

 bird, or may possibly indicate another species of the same 

 genus. In describing this important specimen, the Professor, 

 probably led away by his previous views as to the affinities 

 of the humeri, compares it with Diomedea. It is, however, 

 at once distinguished from the skulls of all the Tubinares by 

 the presence of the distinct transverse hinge-joint between 

 the frontals and the rostrum characteristic of the Stegano- 

 podes, and likewise by the absence of those deep supraorbital 

 grooves which are so conspicuous in the skull of the Alba- 

 tross. Now the presence of such a transverse hinge, coupled 

 with the absence of supraorbital grooves, is one of the most 

 characteristic features of the skull of the Steganopodes ; and 

 when we add to this that the general contour of the specimen 

 (allowing for the effects of crush) is very similar to that of 

 the skull of Sula, while the lateral groove formed by the 

 junction of the two elements of the horny sheath of the 

 rostrum has precisely the same position in the two genera, 

 we shall have no reasonable doubt in concluding that the 

 fossil skull indicates a Steganopodous bird. Further evidence 

 to the same effect is afforded by the depression of the ex- 

 ternal surfaces of the lachrymals, and by the position and 

 contour of the aperture of the posterior nares. 



It is accordingly apparent that both the humerus on which 

 the genus Argillornis was established, and the skull probably 

 referable to the same genus, indicate Steganopodous birds, 

 of which the nearest existing allies are the Gannets. And it 

 may be added that this interpretation of the affinities of these 



