360 
Synopsis of the Birds 
29 7. Larus eburneus, Gm. Pure white ; bill stout 5 feet 
black ; naked space above the tarsus very small; webs some- 
what indented; tarsus one inch and a half; first primary 
longest. 
Young dingy cinereous, somewhat mottled. 
Ivory Gull, Lath. Buff. pi. enl. 994. 
Inhabits the Arctic circle, whence it migrates occasionally 
to the temperate regions of both continents. Forms another 
transition to Sterna, by its feet and wings. 
298. Larus fuscus, L. Mantle slate black ; quills almost 
entirely black, reaching two inches beyond the tail ; bill short, 
not stout ; feet yellow ; tarsus two and a half inches. 
Summer plumage, head and neck pure white : winter, head 
and neck streaked with light browrn. 
Young, blackish cinereous, mottled with yellowish-rusty. 
Silvery gull, Lath. Meyer Vog. Deutsch. ii. pi. 18 . 
Inhabits both continents: very common during winter near 
Philadelphia and New-York. 
299. Larus argentatoides, Brehm. Back and wings bluish- 
gray; quills black at the point, tipped with white, reaching 
but little beyond the tail ; shafts black ; first primary broadly 
white at tip ; second w ith a round white spot besides ; tar- 
sus less than tw o and a half inches ; nostrils oval. Length 
twenty inches. 
Summer plumage, head and neck pure white : winter, head 
and neck streaked with brown. 
Young, dirty mottled, varied with rusty. 
Not noticed m my Catalogue. Somewhat doubtful whether it 
is Brehm' s species. 
Inhabits both continents : common near New-York and 
Philadelphia. We have shot it also on the southern coasts 
of England. 
300. Larus argentatus, Brunn. Mantle bluish-gray; quills 
