$Q -Descriptions of New Fluviatile Shells. 



rictus to point of lower mandible, 21 ; height of bill at the 

 an g le , H; bare space on tibia, 3; tarsus, 21; middle toe and 

 nail, 2* ; inner toe and nail, 13 ; hind toe and nail, h inch. 



Habitat. — California. 



The specimen described was presented to me by E. S. Hol- 

 den, Esq., who shot it on the San Joachin River, near Stockton. 



It belongs to the group of Gulls which includes L. argentatus 

 Linn, and L. occidental Aud. The bill is weaker and more 

 slender than in either of these, that of L. occidentalis being rela- 

 tively large, and having great depth at the angle, the tarsi and 

 toes are comparatively much shorter than in either of the above 

 allied species. The mantle is many shades darker than that of 

 L. argentatus, but not so dark as that of L. occidentalis (which is 

 slate blue), being about intermediate in color. 



The dark feathers on the neck probably denote its winter 

 plumage ; in summer the entire head and neck is, no doubt, 

 white. 



XVI.— Descriptions of New Fluviatile Shells of the Genus Mela- 

 nia Lam., from the Western States of North America. 



By John G. Anthony, Esq., of Cincinnati, Ohio, Corresponding Member. 

 Read January 30 and February 27, 1854. 



In June, 1853, the writer entered upon a pedestrian tour 

 through the States of Kentucky, Tennessee, and part of Georgia, 

 with the double purpose of renovating health, and of collecting 

 the numerous and varied species of fluviatile shells with which 



