PUFFINUS. 433 



brunneis ; subalaribus albis, margine alari brunneo : rostro saturate corneo ; pedibus flavicantibuB, 



digito externo saturatiore. Long, tota circa 17-0, alse 12-0, caudse 5-6, culm. 1-45, tarsi 1-85, dig. med. 



cum ungue 245. 

 $ a mari vix distinguendus. Long, tota circa 17-0, alse 11-5. (Descr. maris et femina ex San Benedicto I. 



Mus. nostr.) 

 Forma ohscurior. Omnino fuliginoso-brunneus, corpore subtus vix cinerascentiore. (Descr. spec, ex San 



Benedicto I. Mus. nostr.) 



Hab. Lower Califoenia, off Cape San Lucas {Anthony ^) ; Eevillagigedo Is., San 

 Benedicto I., Socorro I. (Anthoni/'^^^).— Mexico, Maria Madre I. in the Tres Marias 

 group {Nelson & Goldman ^).— Krusensteen L, N. Pacific ^ ; Volcano Is. ^ ; 

 Hawaiian Is. ^. 



This Shearwater was discovered on Krusenstern Island by Mr. H. J. Snow^, and 

 was afterwards met with by Hoist on Sulphur Island, in the Volcano group ^. Our 

 principal acquaintance with the species rests upon the researches of Mr. A. W. Anthony, 

 who found it in numbers on the Eevillagigedo Islands and off the coast of Lower 

 California ^ "^. Mr. Nelson also observed it near the Tres Marias '^. 



The species is dimorphic and has a white-breasted as well as a sooty phase. The 

 latter has been described by Dr. Stejneger as P. knudseni, from the Hawaiian Islands ^ ; 

 but Mr. Anthony found both forms on San Benedicto, and says that in a series of 

 seventy-five examples every kind of intergradation was noticeable, from specimens with 

 pure white underparts, including the under wing-coverts, to those in grey or sooty- 

 brown plumage. These variations are plainly perceptible in the series in our collection, 

 and it is noteworthy that Mr. Anthony records having taken examples of both phases 

 out of the same hole. 



The same observer states that in the summer of 1897 he noticed this species about 

 Socorro Island, but that it was not common there. None were seen at Clarion Island 

 or west of Eocca Partida on this occasion, but subsequently he met with it at sea 

 near the last-mentioned island. Both phases of plumage occurred, the sooty birds 

 outnumbering the light-bellied ones by about two to one. It was not breeding to any 

 extent at the time of his visit, and only a single egg was obtained. 



Mr. Nelson saw a considerable number of these Shearwaters at sea between Isabel 

 Island and the Tres Marias, and he judged that they must be rather common in 

 these waters. He noticed several among a flock of Sooty Terns which were following 

 a school of porpoises ; but, as a rule, this Piiffinus is found singly, skimming over the 

 sea, making widely sweeping circuits, and pausing occasionally to pick up food'^. 



Mr. Anthony has given a most interesting account of its habits, the bird having 

 been found in abundance in May and June about Cape San Lucas, and between that 

 point and the Eevillagigedo Islands. The southern end of San Benedicto Island was 

 honeycombed with their burrows. He considers that the nesting-season of P. cuneatus 

 is at least two months later than that of either P. opisthomelas or P. auricularis, which 

 both deposit their eggs during the early part of March. A rude attempt at a nest was 

 BIOL. CENTE.-AMEE., Aves, Vol. IIL, April 1904. 55 



