MONOGRAPH OF THE PETRELS. 



the cliffs, extending obliquely downwards. Both sexes, according to Dr. Stejneger, take 

 part in the incubation. 



Adult male. General colour delicate pearly-grey, the under-surface somewhat 

 lighter than the back ; least wing-coverts, as well as those round the carpal bend of 

 the wing, and the upper scapulars, blackish ; median and greater wing-coverts ashy- 

 grey, with narrow white external edges ; primary-coverts and primaries blackish, the 

 latter narrowly fringed with white near the ends ; secondaries broadly edged with 

 white, the innermost dusky like the scapulars ; tail-feathers ashy-grey, dusky towards 

 their tips, the outermost feather externally white ; head light pearly-grey like the back ; 

 base of forehead and lores hoary-grey ; feathers before and behind the eye black ; 

 cheeks and throat greyish white ; remainder of under-surface pure light grey, the 

 lower abdomen and under tail-coverts white, tinged with grey ; under wing-coverts 

 smoky brown, margined with white, the greater series more ashy, hoary-white at their 

 ends ; axillaries also smoky-brown with white ends ; quills ashy below, white towards 

 the base of the inner web ; bill and feet black ; iris dark brown. 



Total length, about 7.5 inches ; culmen, 0.6 ; wing, 6.2 ; tail, 3.3 ; tarsus, 0.9 ; 

 middle toe and claw, 1.1. 



Adult female. Similar to the male. Total length about 8 inches ; wing, 6.2. 



The descriptions are taken from a pair of birds in our collection, procured by 

 Mr. E. W. Nelson at St. Michael's, Alaska. The Plate represents a female bird from 

 Sitka, also in our collection. 



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