392 MB. w, p. PYCRA.FT OS THE [Mar. 21 , 



In Prion there is a tendency towards a distal expansion of the 

 pterygoid, so marked a feature in the Sphenisci. Ill-defined basi- 

 ptervgoidal facets can be traced on the inner border just behind the 

 point where the sliaft rests upon the parasphenoidal rostrum ; just 

 within the inner border of the quadrate articular end is a small 

 pneumatic foramen. 



In the Diomedeidae the pterygoids are relatively longer than in 

 the Procellariidae, they bear no trace of basipterygoidal facets, are 

 quite rod-shaped, and rest upon the parasphenoidal rostrum only 

 by the inner border of their extreme distal ends. The posterior 

 pneumatic foramen is very large. In TJialassogeron the extreme 

 distal end rises, upwards, above the pterygoidal articulation to 

 embrace the rostrum. In Diomedea exidans only does there seem 

 to be a total absence of a dorsal crest. 



The quadrate differs from that of the Storks mainly in the 

 disposition of the mandibular articular surfaces, in the alisence of 

 a pneumatic foramen between the posterior surfaces of the otic and 

 squamosal articular surfaces, and the less marked division between 

 the dorsal aspects of these two processes. The dorsal border is 

 slightly hollowed ; the orbital process large and expanded. The 

 mandibular articular surface is very broad, runs at right angles to 

 the long axis of the skull, and projects inwards considerably beyond 

 the base of the orbital process. There is a very distinct head for 

 articulation with the pterygoid. The outer mandibular condyle 

 is marked by a strong median transverse depression, slopes 

 obliquely backwards, and is separated by a wide groove from the 

 inner, which takes the form of two grooves divided by a median 

 ridge. The quadrato-jugal glenoid caAity lies in the outstanding 

 process at the base of the outer side of the otic process. 



The Mandible. 



As in the Penguins, Storks, and Herons, the dentary suture and 

 the spatula te free end of the coronoid (fig. 1) remain distinct through- 



.a^. 



Inner (A) and outer (B) views of the lower jaw of a nestling 

 Oceanodroma leucorrhoa. 



aruj., angulare ; ar., articulare ; d., dentary ; cor., coronoid ; s.a., supra-angular 



sp., splenial. 



