OF THE UPPER MISSOURI. 179 
C. Recent Mollusca. — 
Recent shells are not abundant on the Missouri except in the streams that flow from 
the North. ‘Terrestrial shells seldom occur above the mouth of the Niobrara river in a 
living condition. The waters of the Missouri to a point above the mouth of Milk river 
~are so turbid that molluscous life does not exist, but in the little streams that issue from 
the mountains, a few Unios are found. ‘The rivers that flow from the north, James, Ver- 
milion and Big Sioux, abound with Unionidae, and other freshwater shells. Vast numbers 
of shells are found in the alluvial deposits throughout the Northwest. In the bank of a 
little stream about two miles below the mouth of the Big Sioux, called Clay creek, there 
is a bed of shells about fifteen feet above the bed of the creek and six feet below the sur- 
face, three feet in thickness, composed almost entirely of different species of freshwater 
mollusca, Unio, Paludina, Physa, Cyclas, Pupa, very finely preserved, many of them deli- 
cate and friable, but as perfect as when living. . In the alluvial just above the shells, are 
great numbers of bones, probably belonging to the buffalo, and over these are growing 
large forest trees, elm, black walnut, oak, &c. Throughout the great thickness of yellow 
marl, which has been deposited along the Missouri, from the Niobrara to the mouth of 
the former river, are disseminated large quantities of terrestrial and fluviatile shells, so far 
as is yet known, mostly identical with recent species. Near Fort Berthold, the fine vege- 
table material washed on the shores of the river contains myriads of minute felives, Pupas, 
&c. From my collections in this region, Mr. Binney has described two new species of 
Pupa, P. Nebraskana, and P. Blandi. In the Black hills very few living shells were ob- 
served, but the alluvial soil composing the banks of the little streams is filled with fresh- 
water and land shells, from which a new species, Helix Cooperi, was described by Mr. 
Binney. The freshwater shells were kindly examined by Mr. Lea of Philadelphia, and in 
regard to the above collection and a series obtained by Mr. Kennicott from the Red river 
of the North, Mr. Lea made the following remarks before the Philadelphia Academy. 
“It is not to be understood that either of these collections, made under adverse circum- 
stances, and at times of great personal danger, should be full representatives of this branch 
of the fauna of these countries. But they are sufficient to prove that zoological life, so far 
as represented by molluscs, is nearly, if not quite the same, as that of the Ohio river basin, 
as well as that of the Missouri river and a part of the Lower Mississippi and Red river of 
the South. ‘The knowledge of a part of the species from these remote districts proves to 
us the wide-spread distribution of the same species, as we find every one of them in the 
Ohio river at Cincinnati, Marietta, and Pittsburg, and this is the more remarkable, as the 
waters of the Red river of the North are embraced in a different system of drainage, flow- 
ing as they do into Hudson’s bay at about 52° north latitude. Here is seen an immense 
