188 MEMOIRS OF THE CARNEGIE MUSEUM 
The most perfect specimens of Demonelix have an average 
diameter of about 6 to 10 inches. Quite often large speci- 
mens are found, that have not the even symmetry of the spiral. 
Again there were others representing, perhaps, burrows made 
by an entirely different animal, large enough at the surface to 
admit parts of askeleton of a larger mammal, such as Professor 
Barbour discovered in an irregular fragment of Demonelix. 
Such, however, might also be burrows that have caved in 
causing the entombment of larger objects partially within the 
burrows. 
A few small colonies of Prairie Dogs (Cynomys lwdovicianus) 
are found on the table land between the Niobrara River and 
the northern exposure of the Miocene formation (‘ Pine 
Ridge”). Our party (consisting of Messrs. T. F. Olcott, A. A. 
Dodd, and the writer) had become so interested in the study 
of Demonelix, that it was decided to make a few experiments 
in digging out the burrows of these recent fossorial animals. A 
quantity of plaster of paris was accordingly purchased, and with 
a large mortar box, a barrel of water, and a supply of sand we set 
out for the prairie dog town, to make some casts of these burrows. 
The accompanying diagrams (Figs. 9 and 10) show,that we were 
partially successful, if not in finding a symmetrical spiral, at least 
in getting casts that were irregular like some specimens of De- 
monelix (see Barbour’s illustrations, figs. 17,18, and 19 in Bull. 
Geol. Soc. Amer., Vol. 8, 1897, pp. 3805-314). There were found, 
in the casts of these burrows, many fine rootlets at a depth of 
4 or 5 feet below the surface. The nest (Fig. 9, d) was well 
bedded with dry grass brought down from the surface. Mixed 
with this bedding were many beetle-wings, 
worms, and remains of grasshoppers. Par- 
ticular attention was paid to the solidity 
of the burrows. It is remarkable how firm 
the walls of these tunnels are in this loose 
and rather incoherent sand, which is a rede- 
position of the eroded Miocene sediment. 
Fia. 8. Spiral and part of ‘‘rhizome”’ of Demonelix, No. 17 (field number). 
Spiral 7 feet and 8 in. long. Many microscopic slides (Pl. XXI.) were taken 
from this specimen. 
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