14 EINAR LONNBERG 
Pterodroma (Aestrelata) cooki defilippiana Gigl. & Salvin. 
Santa iClaras gy ysl: Pats, icwnl eeu A Ol7- 
The total length of two females has been recorded hy Mr. BACKSTROM 
to measure 320 and 315 mm. respectively. The length of wing in the two 
males is 227 and 232,5, in the two females 216 and 229 mm. The length of 
the culmen varies from 26 to 29,3; mm. in these specimens. They thus agree 
completely with the original description (Ibis 1869, p. 64). 
Concerning this species Mr. BACKSTROM has communicated the following 
notes: »During my first stay on the islands, Dec.—April, this bird was not to 
be seen, but on my return in August it was rather plentiful. It bred under 
big boulders down at the shore of Santa Clara, but was not found on Masa- 
tierra. It had not build any nest. According to the inhabitants it laid eggs 
in September.» 
The difference in breeding habits between this Petrel and the following 
closely allied species of Masafuera is especially noteworthy. 
Two eggs of Pt. defilippiana colected by Mr. BACKSTROM on Santa Clara 
the oth of August 1917 hava the following measurements: a) 48 mm. long and 
36,, mm. broad, b) 49 and 35 respectively. 
The breeding habits of this Petrel are evidently very different from those 
of the burrowing P¢. cooki cooki, and this together with the difference in 
external appearance speaks strongly against LOOMIS’ opinion that they should 
be identical. 
Pterodroma (Aestrelata) cooki masafuere n. sp. 
Masafuera: 1 ¢ ?”/2 (Dr. SKOTTSBERG), 3 ddd, 2 PQ 78/2 1917. 
The measurements of these specimens are as follows: 
of of of fe) Q 
Wing... 217 212 Ait 210 218 211 mm. 
Culment 25.5 23,5 25 23,5 23 ZA 
By having the head and hind-neck blackish, much darker than the grey 
back, this Petrel is easily recognized as different from its relative defilippiana 
from the sister island. The measurements also prove that the latter is con- 
siderably larger and has a much stouter bill. 
The least height of the bill just in front of the nasal tubes is in defi- 
lippiana as a rule, about 8 mm. in a dry state (in one specimen only 7,4 mm.) 
but in the Petrel from Masafuera it does not generally exceed 7 mm. and is 
often less. The hook of the bill of the latter is also more slender etc. 
The general colour of the back of defilippiana is paler and more bluish 
than in the smaller species. The former has also more white on the forehead 
