External Structure of Paleozoic Crinoids. 391 
of a long proboscis. It is a most remarkable fact that genera 
which evidently belong to the same group, even species ap- 
parently of the same genus (for instance, Strotocrinus), differ so 
widely in the construction of this organ—some having a long 
massive tube, reaching to several inches above the tips of their 
arms, while others are provided only with a plain lateral 
opening without any superstructure whatever. 
I do not speak at present of the inflated or balloon-shaped 
proboscis of Zeacrinus, Celiacrinus, Poteriocrinus, Hetero- 
ertnus, and similar genera, in which this part is more properly 
called “ the ventral sac,” as it evidently formed a large portion 
of the visceral cavity. Its great size compared with the lower 
cup, the presence of large numbers of small pores, and the 
position of the anal aperture near the bottom instead of at the 
summit, seems to imply that the anal apparatus occupied in the 
internal economy of this sac only a limited space. The in- 
flated sac, accordingly, cannot be homologized with the slender, 
heavy-plated tube of Actinocrinus. We can only compare its 
lateral opening, which is generally placed’ low down near the 
arm-bases, with the anal aperture of species in which the anus 
is located in the ventral disk. 
In addition to its regular functions, the proboscis of Paleo- 
zoic Crinoids may have had the office of expelling the water 
from the system. ‘This suggestion looks not unreasonable, if 
we consider that the solid body of the majority of these Cri- 
noids had apparently no other outlet. I found in one instance 
the proboscis split open longitudinally, and within its inner 
cavity a well-defined narrow tube, filling scarcely one fourth 
of the inner space. ‘This tube may have connected with 
the terminal intestine which I have described above; and the 
office of the surrounding canal may have been to eject the 
deoxygenated water from the body. The fact that some 
Crinoids were provided with a proboscis reaching beyond the 
region of the arms, and others with no proboscis whatever, but 
simply a lateral opening, is easily explained; for if the rejected 
matter were emptied between the arms, it must have come 
constantly again into contact with the arm-currents, which is 
obviated by either plan. This accounts also for the fact that the 
proboscis of some species of Hretmocrinus is constantly turned 
to one side. ‘The proboscis formed a natural support for the 
slender arms; for they are found in most specimens leaning 
closely against it, while in Dorycrinus, which has no proboscis, 
the arms appear always clinging to its long, heavy spines, which 
are evidently not weapons of defence, as some authors have 
supposed, but merely a support and protection for the arms. 
Dr. C. A. White describes, in the ‘Boston Journ. of Nat, 
