THE BIRDS OF AUSTRALIA. 
important, as I have also shown how much differentiation may be expected 
between juvenile and adult. Heteroprion has always a small weak unguis, 
while Pseudoprion has a strong nail, which becomes heavier with age and in 
different subspecies, the culmination being in the subspecies figured. BuUer 
figured in the Supplement (Vol. I., p. 123, 1905) a specimen of P. t. huttoni 
as Prion desolatus. The drawings are rather crude, but there is little 
difficulty in tracing Pseudoprion through figures in literature by means of this 
heavy nail. 
216 
