358 The American Naturalist. [April, 
tion, as it is dead and somewhat eroded. I have very carefully 
examined it, and after comparing it with everything that I 
could think might be related to it, I have come to the conclu- 
sion that it is a form of the protean Unio luteolus. 
This is the most abundant, widely distributed, and variable 
Unio in the world, being found almost everywhere throughout 
the 1,200,000 square miles of the Mississippi drainage basin, 
through Texas, and probably into Mexico, in New York in 
some of the streams that flow into the Atlantic, and northward 
in the vicinity of Hudson Bay, and probably throughout the 
British possessions east of the Rocky Mountains. I have 
traced it up the Missouri River to near its source, and when it 
is taken into consideration that the Marias, a tributary of this 
stream, heads within a few miles of Flathead Lake on Clarkes 
River, a branch of the Columbia, and that the embryos of 
Unios are provided with hooks by which they can attach 
themselves to the feet or feathers of aquatic birds, it is very 
easy to see how this species might have been carried from the 
waters of one drainage system to those of another. Margari- 
tana margaritifera, which inhabits Europe, Northern Asia, and 
the Pacific slope of North America, is also found in the upper 
Missouri. Two specimens of Unio luteolus in the Museum col- 
lection, from the North Shore of Lake Superior, are almost 
exactly like Lea’s type of U. oregonensis. 
So far as I am aware, nothing is stated of Unio famelicus, 
the other Pacific slope species, save that Gould received his 
type from Dr. Pickering, and that it is said to have come from 
Walla Walla, Oregon. The type is in the National Museum, 
and is undoubtedly a young Unio ellipticus Spix, from Brazil, a 
species belonging to an extensive South American group, 
characterized by having oblong, compressed, sulcate shells, 
which are often granulated on the ridges. Any one familiar 
with Unios would know at once on carefully examining the 
type, that it came either from South America, or some part of 
the Southern Hemisphere of the Old World, a fact which is 
made evident by its form, its peculiar greenish olive epider- 
mis, the strong growth lines, and, most of all, the compressed, 
parallel, cardinal teeth of the right valve. It is perfectly safe 
to say that the locality given is an error, and that this species 
was never found in the United States. 
