558 
PROCEEDINGS OF THE ACADEMY OF 
Gavia fusca, Brisson, Ornith. pi. xviii. fig. 2. 
Sterna stolida , Linn., S. N. 1766, i. 227, et auct. antiq. 
Anous stolidus , G- R. Gray, Gen. Birds, 1849, iii. 661, et auct. recent. 
Megalopterus stolidus, Keys, et Bias., Wirb. Eur. 1840, 98. 
Anous niger , Stephens, Gen. Zool. 1826, xiii. 140. 
A comparison of the Floridan bird with that from the South Pacific, collected 
by Wilkes’ Exploring Expedition, shows some differences of color, form and 
size, which, though not great, are well marked and quite constant in all the 
specimens I have examined. The bill of the Pacific bird is of the same length 
as that of the American, but is higher at the base, which gives it a somewhat 
different shape. The toes are considerably longer, while the tarsus is of just 
the same length ; making a different relative length of tarsus and toes. The 
wing is from a half to three-fourths of an inch longer ; the tail is very decidedly 
longer, the difference being quite an inch. The central. tail feathers are half an 
inch shorter than the lateral feathers in the Pacific bird ; while in the American 
the emargination is much less, only about a fourth of an inch. The differences 
in color are slight. The American bird has the occiput bluish plumbeous, 
which fades into pure white on the crown anteriorly; while the Pacific bird 
has the occiput darker, and the crown ashy white instead of pure. The sides 
of the head and neck all round, in the American bird, have a bluish plumbeous 
wash, notably different from the general fuliginous, which is entirely wanting 
in the Pacific bird. The feet of the American bird appear much darker in the 
dried skin. 
Mr. Cassin, in the Ornithology of the Expedition, remarks upon these differ- 
ences in the following words : “ Numerous specimens from the shores and 
islands of the Pacific Ocean present, with some degree of uniformity, small and 
apparently unimportant differences from others from the Atlantic coast of North 
America. The bill appears to be larger in the latter, and a slight dissimilarity 
is observable in the colors. On careful comparison, however, we are not in- 
clined to consider the bird of the Pacific as possessing characters sufficient to 
justify a distinct specific designation ; but venture to suggest that further 
examination of specimens from localities in the two great oceans, and especi- 
ally of the various immature plumages, is yet desirable.” 
1 tabulate the differences between the two, leaving it to future investigation 
Pacific Bird. 
Length of wing 11-00 to 11*25. 
Length of tail about 7-00. 
Height of bill at base -43. 
Length of tarsus 1*00 (same). 
Length of middle toe and claw 1*60. 
Middle toe and claw 1-60 hundredths 
of tarsus. 
Central tail feathers -50 of an inch 
shorter than next. 
Occiput brownish ash, becoming ashy 
white (not pure) on the front. Sides 
of head and neck not notably different 
from general fuliginous. Feet reddish 
brown in dried skin. 
The difference in color appears very slight. I attach more importance to the 
discrepancies in size and proportions. If the Pacific bird be really distinct 
from the American, it has probably yet to receive a name ; for it is very differ- 
ent from the various species of Anous mostly described by Mr. Gould. In that 
event, it may be called a Anous frater. 
In the preceding pages are noticed all the Terns which are known to inhabit 
[Dec. 
to determine their constancy and value 
American Bird. 
Length of wing 10-00 to 10-50 inches. 
Length of tail about 6-00. 
> Height of bill at base -38. 
Length of tarsus 1 00. 
Length of middle toe and claw 1 45. 
Middle toe and claw 1-45 hundredths 
of tarsus. 
Central tail feathers but slightly 
shorter than the next. 
Occiput bluish plumbeous, becoming 
pure white on the front. Sides of head 
and neck all round with a decided 
wash of bluish plumbeous. Feet nearly 
black in dried skin. 
