External Structure of Paleozote Crinoids. 389 
furrow of Cupressocrinus is very similar to that of Cyathocrinus. 
Ina section of the arm of this genus I readily distinguished, by 
transmitted light, the food-groove, which has a narrow and deep 
outline, a canal on both sides of it; and I have but little 
doubt that the arm-furrows were similarly constructed in all 
Paleozoic Crinoids. 
3. The Alimentary Canal. 
Meek and Worthen publish, in the ‘Geological Report of 
Illinois,’ vol. v., most excellent descriptions and figures of an 
organ which occupies the greater part of the visceral cavity of 
Paleozoic Crinoids ; they call it, from its position, in analogy 
with other Echinoderms, “ the digestive organ.” It is a large 
convoluted body, resembling in outer form and outline the shell 
of a Bulla, with a longer vertical axis, and open at both ends. 
The upper end is placed below the centre of the ventral disk, 
the lower one directed toward the column, dilated above, con- 
tracted below, coinciding with the inner space of the visceral 
cavity, to the walls of which it stands nearly parallel. In some 
cases it 1s subcylindrical and slightly truncate at both ends. 
The organ is constructed of a great number of very minute 
pieces or bars with intervening meshes; but its delicate texture 
is but seldom observed, owing to the presence of incrustations 
of calcareous or siliceous matter, which fill up the meshes and 
give to the structure a rather dense appearance*. 
The convolutions are directed outward from left to right, 
varying in number from two to four in different species. 
Judging from external appearance only, the convoluted walls 
of the organ appear as mere partitions leading to the inner 
chamber of a Bulla-shaped body. This, however, is not the 
fact. xamining the so-called walls in some transverse sec- 
tions, I find them to be coiled, without touching each other at 
any point, and composed of two distinct partitions, placed side 
_ by side and closed at the edges, thus proving that the ap- 
parent walls are the coiled organ itself. According to this, the 
digestive organ consisted of a long flattened canal, rounded at 
the outer side, widest in the middle, tapering rapidly at both 
ends to a rather heavy flattened tube, the outer end ascending 
spirally toward the top of the visceral cavity, making two or 
more turns, while the inner one, winding in a spiral way around 
its Own axis, passed upward to near the centre of the dome. 
* To these incrustations, which are evidently deposits from the water, we 
owe, inagreat measure, the preservation of these delicate organs; and as they 
are comparatively thicker in adult specimens, they seem to haye accumu- 
lated already during the life of the Crinoids, and may have caused, in 
many instances, their death, 
