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IOWA ACADEMY OF SCIENCES. 
up, but the majority were about straight. Their prevail- 
ing position is: cephalic portion extending horizontally 
near the surface of the stratum and just appearing at its 
surface, thorax and pygidium extending downward through 
the stratum. Different sized individuals maintain the 
same upper level at the upper surface of the stratum, the 
larger ones extending farther downward. Their heads 
sometimes appear flattened as if from vertical pressure,, 
while the thoracic portions are doubled, bent and distorted 
in several specimens as if from the same cause. 
As to why every one of these animals, at the place 
mentioned, should be found cephalon up we must seek the 
explanation in their habits. But this quest involves us at 
once in difficulties because the entire sub-class of which 
they were members became extinct long ago. We have 
the authority of Zittel * that little is known of trilobites* 
habits. It is known from the fossil remains of brachiopods, 
crinoids, etc., found in their company, that they were salt 
water animals. Some species preferred deep water, others 
shallower, and one genus, Trinucleus, lived partly buried 
in the mud. 
The uniformity of position of such a number of fossil 
remains would defeat the supposition that they were mere 
empty carapaces shed by moulting individuals. In that 
case we should have found some remains horizontally 
placed, or axis downward, or pygidium upward instead of 
all in the same position. Their pygidia would not have 
been of sufficient density to sink, and at the same time 
their cephala buoyant enough to float. If carapaces, some 
should certainly have had facial sutures open or free cheeks 
missing. 
If, then, as seems evident, they took the position in 
which they were fossilized, voluntarily as living creatures, 
can we not from that fact find some light on their condi- 
tion at that time? It does not seem possible that they hid 
themselves in burrows, because of their being marine 
rather than land animals. Their bent and distorted con- 
dition also would hardly be the position of such an animal 
* Zittel, Text-Book on Paleontology, Eastman’s trans. 1, 617. 
