THE BIEDS OF AUSTRALIA. 
Examination of the preceding cuts in conjunction with the letterpress, 
shows the points to note. It will be seen that the bill of Thalassarche 
recalls that of Phoebastria, the chief point of difference being the presence 
of a cere, at the base of the latericorn, which sharply separates the latericorn 
from the feathering. The culminicorn posterior to the nasal opening reaches 
to the latericorn, but does not overlap it as in Plio&hastna. The base of the 
lower mandible shows an angle, which is not deep as in Diomedea, but is pro- 
tected by a cere: in the young this angle is more pronounced, showing clearly 
the reduction from a deeper entrant, and admits the suggestion of evolution 
from a groove-bearing form. I hope these cuts show the close alliance of the 
two generic t3^pes Thalassarche and Thalassogeron, and the greater differences 
between Thalassarche and Diomedea, 
266 
