MONOGRAPH OF THE PETRELS. 



Nectris, Kuhl, Beitr., p. 144 ; Coues, Pr. Acad. Nat. Sci. 

 Philad., 1864, p. 123. 



Thyellas, Gloger, in Froriep's Notizen, XVI., p. 279 (1827) ; 

 Salvin, Ibis, 1888, p. 353. 



Thiellus, Gray, List Gen. Birds, 1840, p. 78 ; Bp., Consp. 

 Av., II., p. 200 (1856) ; Coues, Pr. Acad. Nat. Sci. 

 Philad., 1864, p. 122 



Gymotomus, Macgill., Man. Brit. Birds, p. 13 (1842) 



Ardenna, Reichenbach, Syst. Av., p. iv. (1852) 



Thyellodroma, Stejneger, Pr. U.S. Nat. Mus., XL, p. 93 

 (1888) 



Zalias, Heine, Nomencl. Mus. Hein., p. 362 (1890, vice 



-/ ft/Z&lLlAsS ) . a •• • • •• •• •• •• 



P. gravis 

 P. anglorum 



P. sphenurus 

 P. gravis 



leucomelas, p. 72 



Key to the Species. 



a. Tail long, wedge-shaped. 



a', Under-surface white ; feathers of the head, sides 

 of neck, and upper plumage generally sooty- 

 brown, conspictiously edged with white 



b'. Under-surface white ; feathers of the head and 

 upper plumage not edged with white 



a". Back, greater coverts and primaries entirely 

 sooty-brown . . 



b" . Back and greater coverts grey ; inner half 

 of inner web of primaries white 



c'. Under-surface sooty-brown, like the upper- 

 surface . . . . chlororhynchus, p. 84 ; cuneatus (dark phase), p. 76 



b. Tail shorter, rounded, sometimes slightly wedge- 



shaped 



d'. Under-surface white.* 



c". Larger ; wing 12 inches and upwards. 



a'". Back and upper tail-coverts incon- 

 spicuously edged with pale dusky- 

 brown ; crown darker than the hinder- 

 neck. 



* Sometimes mottled with ashy-brown (P. gravis ; P. yelkouanus). 



cuneatus, p. 76 

 bulleri, p. 81 



XL 



