154 CALIFORNIA ACADEMY OF SCIENCES _ {Proc. 47H Ser. 
lower tail-coverts and the base of the tail are more or less 
white. 
Of the Expedition series, twelve specimens were taken on 
the 4th and 5th of January, four on April 24, sixteen between 
the 4th and 11th of May, twenty-six between the 7th and 18th 
of June, fifteen on the 22nd and 25th of July, six between the 
Ist and 14th of August, eight on the Ist, 2nd, and 15th of Sep- 
tember, five on the 4th, 5th, and 12th of October. Although 
by no means complete, this series affords a fair clue to the 
moult of the species. In the January specimens feather re- 
newal is practically at a halt. In an April bird the first and 
second primaries. are not fully grown. ‘The first primary is 
also backward in a bird of May 7, in one of May 10, and in 
three of June 18. According to some of Mr. Beck’s labels, 
great enlargement of the sexual organs prevails during May 
and June, indicating the height of the breeding season in 
Galapagos waters. Most of the specimens obtained in July 
were undergoing a complete moult. As in the moulting of 
other petrels, the degree of advancement varies in different in- 
dividuals. August and September specimens, as a whole, 
manifest further progress, while October ones, in most in- 
stances, show an abrupt decline in feather growth. 
The dimensions in millimeters of fifty-four males and seven- 
teen females are summarized in the subjoined table. 
Sex Wing Tail Culmen Tarsus Hee and 
IMiasxianntriaa yin of 143 66 13.8 2S tl 21 
IMiaaracina eee enn (of 130 54 11.4 20 18 
Mies eae on 137 59 12.6 22 19.5 
Mie ssimaibhan., | 54000505- Q 145 67 14 23.3 21.3 
Miramar e 2 132 55 11.8 20.2 18.1 
Cate nea ta eta Q 137 59 12.7 21.8 19.7 
No marked difference in the dimensions of the sexes is mani- 
fested in the preceding summary. 
