218 The American Naturalist. [March, 
great core of a color similar to that of the surrounding rock. 
‘This is not quite as hard as the external white ring and often 
shows sections of large white tubular structures. 
What this so-called “corkscrew” may be may remain in 
mystery for some time to come. The sponge-like appearance 
of some of the specimens seemed to proclaim it a gigantic fresh 
water sponge. But microscopic examination brought forth no 
evidence of the spicules that one would expect. All that could 
be found of an organic nature was in one or two instances a 
few plant cells. The presence of these, however, might be ex- 
plained as living cells of rootlets that had worked into the fos- 
sil and in no way belonged to it. In one instance a nearly 
entire skeleton was found in a stem near its junction with its 
spiral and suggested the idea that our fossil might be nothing 
more than the core of a rodent hole. Still another supposition 
was that it is only a concretionary formation. The peculiar 
and regular form, lack of concretionary structure, and wide- 
spread occurrence at once throws aside the last supposition. 
The regularity of the spiral, the “ pole ’-like structure in some 
of the spirals, the fact that the spiral tapers from top to base, 
and sometimes may have tapering root-like ends, and finally 
the presence of tubular structures within the spiral and stem, 
demonstrate the untenability of the “burrow” idea. If the 
“cork screw” was the underground stem and root of some 
aquatic plant it becomes very difficult to explain the presence 
of the skeleton. If it is supposed to be of a sponge-like nature 
and growing above the lake bed, the presence of the skeleton 
may readily be accounted for. It might become entangled in 
the growing sponge mass and surrounded, just as any pebble 
or shell may be found to be covered by some existing sponges.’ 
The uniformity with which the “stem” occurs points to a 
mode of growth that finds its analogy among some of the 
1 Since this paper was written, I have seen a paper by Prof. Barbour giving the 
last results of his studies. Sections have been made from all parts of the fossil 
and from numerous specimens with the uniform result of demonstrating the pres- 
ence of plant cells. These have an average size of 35 to 50 by 16 microns and 
an evidently parenchemyous nature. Since no others are found, the structure 
must have been very low in the scale of life. 
See University Studies, University of Nebraska, July, 1894. 
