220 
ANAS VALISINERIA. 
general whiteness of its plumage. A short comparison 
of the two will elucidate this point : The canvass-back 
measures two feet in length, by three feet in extent, 
and when in the best order weighs three pounds and 
upwards. The pochard, according to Latham and 
Bewick, measures nineteen inches in length, and thirty 
in extent, and weighs one pound twelve or thirteen 
ounces. The latter writer says of the pochard, “ the 
plumage above and below is wholly covered with prettily 
freckled slender dusky threads, disposed transversely in 
close set, zigzag lines, on a pale ground, more or less 
shaded off with ash a description much more applicable 
to the bird figured beside it, the red head, and which 
very probably is the species meant. In the figure of the 
pochard given by Mr Bewick, who is generally correct, 
the bill agrees very well with that of our red head ; but 
is scarcely half the size and thickness of that of the 
canvass-back ; and the figure in the Planches Enluminees 
corresponds in that respect with Bewick’s. In short, 
either these writers are egregiously erroneous in their 
figures and descriptions, or the present duck was 
altogether unknown to them. Considering the latter 
supposition the more probable of the two, I have 
designated this as a new species, and shall proceed to 
detail some particulars of its history. 
The canvass-back duck arrives in the United States 
from the north about the middle of October, a few 
descend to the Hudson and Delaware, but the great 
body of these birds resort to the numerous rivers 
belonging to and in the neighbourhood of the Chesapeake 
Bay, particularly the Susquehannah, the Patapsco, 
Potowmac, and James’ rivers, which appear to be their 
general winter rendezvous. Beyond this, to the south, 
I can find no certain accounts of them. At the Susque- 
hannah, they are called canvass-backs ; on the Potowmac, 
white-backs ; and on James’ river, sheldrakes. They are 
seldom found at a great distance up any of these rivers, 
or even in the salt water bay ; but in that particular 
part of tide water where a certain grass-like plant 
grows, on the roots of which they feed. This plant, 
