C. Wachsmuth—Structure of Paleozoic Crinoids. 119 
that it was removed by the least touch. The substance of 
which the casts are formed appears to have been a fine silicious 
mud which could penetrate the smallest pores. The internal 
organs are of course not preserved, but their impressions at the 
surface of the casts throw much light on the structure beneath 
the vault. The center of radiation appears here a small pen- 
tagonal, rounded, or in species with strong subcentral proboscis, 
subtriangular or even heart-shaped space or plane, enclosed by 
a deep groove, from which, in some of these specimens, ele- 
vated ridges, alternating with depressions, pass out toward the 
arms; but before quite reaching them, there proceeds, from be- 
low the ridges of the casts to every arm, a smaller ridge which 
clearly indicates the tubular canal, as described in Actinocrinus 
proboscidialis, The casts are so perfect that I can even detect 
at some places the impressions of the alternating minute plates 
of the tubes. 
orming the casts; 
closely underlie the test, and their counterparts are preserved. 
ve no annular groove, and the radiation which is marked 
by elevated rounded ridges, almost like strings overlying the 
nt % enter where I noticed th 
the arm-bases in the same manner as the tubular canals; they 
are stronger toward the center, decreasing in size with each bifur- 
cation. That these ridges are remains of muscular cords is not 
Probable from the perishable nature of such organs, and they 
are not their casts, or they should have left depressions in place 
of elevations. They can only be casts of passages which com- 
Municated with the central aperture, and which were evidently 
oa 
