OCEANODROMA. 431 
3. Oceanodroma socorroensis. 
Oceanodroma socorroensis, Towns. Pr. U. S. Nat. Mus. xiii. p. 134°; Salv. Cat. Birds Brit. Mus. 
xxv. p. 3527; Anthony, Auk, 1895, p. 387 *; 1898, p. 38‘; Oates, Cat. Eggs Brit. Mus. 1. 
p- 149, t. 11. fig. 6°. 
Oceanodroma townsendi (nec Ridgw.), Anthony, Auk, 1894, p. 321°. 
O. melanie similis, sed minor, plaga brunnea alari paullo magis extensa, tectricibus medianis anticis quoque 
brunnescentibus; supracaudalibus lateralibus seepius cinerascentibus, interdum albidis; subalaribus 
rufescenti-brunneis, marginalibus nigerrimis: rostro et pedibus nigris. Long. tota circa 7°8, ale 5:9, 
cauds 2°95, culm, 0°61, tarsi 0-8. 
Q mari similis. Long. tota 7-5, ale 5°85. (Deser. maris et femine ex San Benito Is. Mus. Brit.) 
Hab. Cauirornia, as far north as the Santa Barbara Channel, San Diego%, San 
Benito Is. (Anthony®); Revittaeieupo Is., Socorro I. (Townsend * *). 
This species is described as similar to 0. homochroa, but with the wings longer, and 
the tail shorter and less deeply forked, the tarsus and toes shorter, the sides of the 
rump whitish, and with no white on the under surface of the wings. The dimensions 
are given as follows: —Wing 5:50, tail 2°75 (forked for 0°50), culmen 0°55, tarsi and 
toes 0°85 1. 
Only one specimen was secured and a few others seen, but Mr. Townsend found the 
hills at the western end of Socorro Island literally honeycombed with the burrows of 
some creature which he believed to be this Petrel. The most diligent search did not 
reveal any small mammal on the island, and lizards could not have excavated these 
burrows !. 
This is a smaller bird than 0. melania, which otherwise it closely resembles. The 
light patches of whitish or grey appear to be by no means a constant character, as 
Mr. Anthony has already remarked. The type-specimen has whitish patches on the 
sides of the rump (i. ¢. the lateral upper tail-coverts), but in over one hundred skins 
he has found only about 3 per cent. so marked. A few were nearly as white on the 
rump as O. leucorrhoa; but the largest part of the series, fully 95 per cent., had 
sooty-black coverts above and below. ‘Iwo or more species, he adds, might be 
made, but unfortunately the light-rumped birds are found in the same burrows with 
the dark ones. 
Specimens of 0. socorroensis have also been obtained off San Diego, California, so 
that the species is now included in the avifauna of the United States °. Mr. Anthony 
has also found it nesting on the San Benito Islands, between Guadalupe I. and the 
Cerros Is., and has presented specimens of both birds and eggs to the British Museum. 
He says that it is found on the open sea, in small companies of not more than three 
together °. 
The eggs are elliptical in shape, white, marked with pink specks and dots at the 
broader end. In one egg these form a cap, in the other an indistinct zone, a few 
specks being also scattered over the shell °. 
