THALASSOGERON. 
of the last-named, Th, cautus, is again different from either of the preceding : 
it is altogether a larger and more stout bill, and the culminicorn is separated 
from the basal feathering by a wide space of fleshy membrane, and the 
culminicorn does not become reduced but is almost wider at its base than 
in the middle. It is certainly subgenerically separable, and I introduce 
for it the subgeneric name DIOMEDELLA, with type the only species 
Th. cautus Gould. 
As a matter of fact Dioynedea cauta Gould is quite an aberrant Mollymawk 
standing apart from the other members of Thalassarche and TTialassogeron in 
size as well as bill-characters, and is certainly as worthy of generic distinction 
as is Th. cuhninatus, but inasmuch as the latter species was first chosen for 
the honour and has been commonly accepted, I use it, but there seems to me 
little doubt that the correct nomenclature is not yet fixed. 
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