1070 The American Naturalist. [December, 
ROCKY MOUNTAIN RHIZOPODS. 
BY EUGENE PENARD, SC.DR. 
TIONN a stay which I made this year in the mountains of 
the state of Colorado I gave some of my time to the study 
of the fresh-water Rhizopods, comparing them with those I had 
observed in various regions ‘cf Europe. I should like to give 
here the results of my comparisons. 
All the organisms which are treated of in this paper have been 
found in the neighborhood of Caribou, a small mining town north 
of Boulder, and about 10,000 feet above the level of the sea. At 
this altitude Rhizopods are still numerous, as Leidy has shown 
in his remarkable work on the fresh-water Rhizopods of North 
America. He found them abundant in the Uinta Mountains, 
Wyoming, at 10,000 feet—the highest altitude, I believe, at 
which these organisms have & yet been found. However, as 
will be seen later, my gatherings at 12,000 feet have been very 
productive, which is after all not to be wondered at, knowing the 
very great capacity of these organisms for resisting either cold or 
heat, or any other disturbing element. In fact, they can be 
expected to be found everywhere, provided there are mosses and 
humidity, and if I have not found them higher (except one 
species, Difflugia constricta, at 12,500 feet), it is only because 
the ground was unfavorable to the presence of quiet water, and 
that my investigations at these higher altitudes have been very few. 
I have no intention to speak about the organization and phy- 
siology of these organisms. Leidy, in his beautiful work, has 
treated the subject at length. I would simply like to give a list 
of the species I have found in the Rocky Mountains, adding 
some remarks about a few of them, and finishing with some 
observations on the structure of the shell in these animals. 
This structure is not very well known in most of the species ; 
and as I have in these latter years accumulated a good 
many observations in this connection, I venture to detail them 
here, in the hope that they will prove of some interest. 
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