External Structure of Paleozoic Crinotds. 387 
have involved that of the entire covering. I therefore believe 
these plates were not firmly attached in the living animal, but 
merely leaned against each other as well as upon the tooth-like 
projections, being only attached to the inner edge of the 
quadrangular plates by muscular or interarticular substance, 
and that they were, inanalogy with similar plates in recent 
Crinoids, movable. This seems further confirmed by the 
construction of the plates themselves, and especially by the 
manner of their attachment. The inner edges of the qua- 
drangular plates (between the projections) being slightly con- 
vex, they rested in regular sockets, which facilitated their open- 
ing in an outward direction. In case these plates, as I can no 
longer doubt, could be opened or closed, it seems reasonable 
that they were open in my specimen when the animal died ; or 
they otherwise would have been preserved. 
The position and construction of the inner channel proves 
most satisfactorily, and in analogy with recent Crinoids, that it 
contained the food-groove which conveyed the food through the 
arm-openings beneath the vault to the oral aperture. The 
small movable plates are evidently homologous with the 
“‘Saumplatten ” of Antedon; and the imbrication of these 
plates, as well as of the entire covering, seems to hint at the 
conclusion that the furrow was always closed when the arms 
were folded up as in Mr. Springer’s specimen, but that, on the 
contrary, aS in my specimen, the furrow was open when the 
arms were spread, and that in this position the animal took in 
its food. 
In describing the covering of the furrow, I have ‘already 
mentioned the presence of two rows of small pores located at 
the angles of the triangular pieces. There is nothing to indi- 
cate that these pores were sockets of pinnule ; if they had been 
the ‘‘ Saumplatten” could not have opened. From their posi- 
tion I infer they were passages for tentacles connecting with 
parts of the inner tube. If this is correct, it seems to me 
there must have been located within the tube a passage in 
connexion with the ambulacral system, since the ‘tentacles 
form a part of it. ‘This is evidently the case. In a transverse 
section of the arm, with the help of a magnifier, I think I have 
detected within the tube traces of two passages—a deep groove 
occupying only the median region, and on each side of it a 
small canal underlying the pores. ‘The condition of the spe- 
cimen does not enable me to say whether the two side passages 
connect at the bottom or not; but in either case they un- 
doubtedly represent the ambulacral canal, the food-groove 
occupying only the median and upper part of the channel. 
It is to be regretted that in no instance the upper part of 
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