Order PROOELLARIIFORMES. 
Family TEA LA SSI I) ROM I I)R. 
No. 115. 
CYMOCHOREA CASTRO. 
(CRYPTOLEUCURA.) 
MADEIRAN FORK-TAIL PETREL. 
Thalassidroma castro Harcourt, Sketch of Madeira, p. 123, 1851. Deserta Island, near Madeira. 
Eigured Godman, pi. 5. 
Distribution. Atlantic Ocean. 
Cymochorea oasteo ceyptoleucuea Ridgwav. 
Cymochorea cryploleuc.ura Ridgwav, Proc. U.S. Nat. Mus., Yol. IV., p. 337, March 29th, 1882. 
Kauai, Hawaiian Islands. 
Distribution. Hawaiian Islands, accidental to Australia. 
Adult. General colour above dark sooty-black, including the wing and tail-feathers, upper tail- 
coverts, forming a white patch, white at the base and with wide black tips ; outer 
tail-feathers with white at the base ; secondary coverts brown, showing a wing-bar; under¬ 
surface sooty-brown including the wing lining and axillaries ; vent and central under tail- 
coverts dark-sooty ; side ones white. Wing 157, tail 70, culmen 15.5 ; tarsus 21.7 ; 
middle toe and claw 22.8. 
The sexes are alike. 
Nest. At the end of a burrow. 
Egg. Clutch one ; white without gloss, with a more or less evident zone of reddish spots round one 
end. Average measurements, 33.5 by 24.8 mm. 
Breeding-season. June (April to July). 
I am including a drawing of the upper tail-coverts and tail of Cymochorea leucorhoa 
and C. castro, the only two species in the genus which could possibly be confused. 
The former has been recorded from New Zealand and the latter is now added to 
the Australian List because of a bird in the British Museum labelled “ Australia.” 
To distinguish them we have the following :— 
leucorhoa has the base of the outer tail-feathers whitish right at the base; 
the central upper tail-coverts not definitely white, the others white, 
sometimes tipped and edged with black and with brownish shafts; 
under tail-coverts dark ; tail measurement more than, or about equal, 
to hah the Aving measurement. (Right-hand figure.) 
castro has the base of the outer tail-feathers quite white for an inch or more; 
all the upper tail-coverts definitely white, Avith Avell-marked black tips 
and Avith Avhite shafts ; the outer under tail-coverts AA r hite, central 
ones and A r ent dark ; tail measurement less than half the Aving. 
In perfect specimens leucorhoa has a more deeply-forked tail, otherwise the 
birds are dark and of about the same Aving measurements. 
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