532 NATATORES. THALASSIDROMA. 
the base, darker towards the tip, slender, one inch and 
three-eighths in length from the forehead to the tip. 
Legs having the tarsi much compressed; front of the 
tarsi, and part of the webs and toes yellowish, tinged 
with flesh-red. 
Genus THALASSIDROMA, Vircors. STORM- 
PETREL. 
GENERIC CHARACTERS. 
Bint shorter than the head, much compressed in front of 
the nasal sheath, with the tip of the upper mandible sud- 
denly curving and hooking downwards, and that of the lower 
one slightly angulated and following the curve of the upper. 
Nostrils contained in one tube or sheath, but shewing two 
distinct orifices in front. 
Wings long, acuminate, with the first quill-feather shorter 
than the third, and the second the longest in the wing. ‘Tail 
square, or slightly forked. 
Legs having the tarsi rather long and slender, reticulated. 
Feet of three toes, united by a membrane. The outer and 
middle toes nearly equal in length, and longer than the 
inner ; hind toe represented by a small strait dependant nail. 
The members of this genus, which are all of small size, 
have been very properly separated by Mr Vicors from the 
rest of the Petrel group, as they exhibit a decided difference 
jn the form of the bill from that of the Shearwaters and the 
other nearly allied species, the lateral compression towards 
the tip being much greater ; and the nostrils, instead of being 
separate tubes, contained in a common sheath, and merely 
divided by an internal septum. The proportions of the wing 
are also different, and their legs are longer and placed more 
in the centre of the body. In TEemmrncx’s “ Manuel,” they 
