404 ME. w. p. PTCEAFT ON THE [Mar. 21 , 



downwards beyond the level of the tomium, nor extending backwards 

 into the lachrymo-nasal fossae ; interorbital septum perforate. 



Procellariid^. 



a. Width of the basitemporal plate slightly or not at all exceeding the length 



of the pterygoid Procellariince. 



b. Width of the basitemporal plate much exceeding the length of the 



pterygoid — very slightly less than the distance between the quadrates. 



PelecanoiditKe. 

 (One genus only, Pelecanoides.) 



B. Supra-orbital groove with a more or less extensive overhanging ledge, the free 

 edge of which is flattened ; temporal fossae represented by shallow semi- 

 circular depressions of uniform depth, separated each from its fellow by the 

 broad, quadrangular, shield-shaped roof of the skull ; external nares small, 

 opening laterally underneath a broad eulmen ; orbitosphenoid completely 

 ossified ; length of the upper jaw greatly exceeding that of the cranium ; 

 basipterygoid processes absent, with the parasphenoidal pneumatic aperture 

 opening above the Eustachian groove in a narrow chink ; palatines closely 

 approximated in the middle line so as nearly to conceal the vomer ; palatines 

 relatively short, becoming fused distally with the maxillo-palatine processes, 

 which project downwards far below the level of the tomium; maxillo- 

 palatine processes large, more or less fenestrated, extending vertically up- 

 wards and backwards into the lachrymo-nasal fossa DiOMEDEiDyE. 



Key to the Genera of ProcelJariinae. 



Group A. Supra-orbital grooves, shallow but very wide, semilunar in shape, 

 almost or quite meeting in the middle line ; lachrymal free, with a wide 

 chink between its dorsal border and the frontal; temporal fossae feebly 

 developed or absent. 



a. Without spine-like wings behind the supra-orbital grooves. 



a'. Basipterygoid processes absent ; maxillo-palatines approaching the 

 mid-ventral line, distinct from the palatines ; supra-orbital grooves 

 separated by a thin linear ridge Oceanites. 



b. With a conspicuous pair of " wings " behind the supra-orbital grooves. 



b'. Basipterygoid processes vestigial — in the form of prickles ; maxillo- 

 palatines approaching in the middle line, and partially fused with the 

 palatines. 



a". Supra-orbital grooves separated by a shallow median groove. 



Ci/7nodroma. 

 b". Supra-orbital grooves separated by a median linear ridge. 



Fregetta. 



c\ Basipterygoid processes absent ; maxillo-palatines approximating to 



the middle line, and quite distinguishable from the anterior ends of 



the palatine ; supra-orbital grooves separated by a thin linear 



ridge Pelagodroma. 



Group B. Supra-orbital grooves very narrow, excavated out of the free edge of 

 the frontal and separated by a very broad interorbital median ridge. 



a. Basipterygoid processes represented by minute prickles ; lachrymal free, 

 its dorsal border closely applied to the frontal ; maxillo-palatine processes 

 concealed from below by the palatines Procellaria. 



Halocyptena ^. 



Oceanodroma. 



1 Adult skulls of Halocyptena and Oceanodroma not represented in the 

 Museum collections. 



