' 
acs hate SEs oS a TS oe a PR PPh See. ti Pie gL ke 
Sed. Salli : : 
Meek and Worthen on Paleozoic Crinoidea. 39 
the space between is found to coincide very closely with that 
between the inner sides of the arm-bases protruding from the 
sinuses. Hence it is evident that the shell had commenced 
forming these sinuses in its lip exactly at the period of its 
growth, when it had attained a breadth that brought the edges 
of its | iip in contact with the arm-bases. After this, it had in- 
creased very little in breadth between via arms of the Crinoid, 
though it ha grown somewhat wider above and below, an 
nearly doubled its length. Whether or ih it covers the open- 
ing in the side of the vault of the Crinoid we are unable to 
say, since the folded arms (which are, as usual in these cases, 
well preserved), and adhering matrix, cover the vault. We 
have scarcely any doubt now, however, that the Platyceras 
does, in this, as in most of the other cases, actually cover the 
opening in the side of the vault of the Crinoid. 
m the facts stated it is, we think, swilend that these 
mollusks actually lived long enough after their connection 
e Crinoids, to which we find them attached, not only to 
Mites sdanied the "edges of their lip to fit the surface of the 
Crinoid, but to have generally increased more or less in size, 
and in some instances, at least, to have actually nearly or quite 
doubled their size. Admitting this to be the case—and we 
think there can be no reasonable doubt on this point—we can 
no longer believe that these Crinoids were preying upon the 
mollusks ; and we therefore think no well grounded arguments 
can be based u upon the fact of their being so frequently found 
attached in the manner described, in favor of the conclusion 
that the opening in the vault of these Crinoids is the mouth. 
But, if they were not in the habit of eating these mollusks, 
it may be asked what could have been the nature of the rela- 
tions between the two, that so frequently brought them to- 
gether as we now find them? The first explanation that sug- 
gests itself is, that possibly the mollusk may have been preying 
upon the Crinoid. But the fact, already stated, that these 
mollusks evidently lived long enough attached to these Cri- 
noids, as we have every reason to believe, during the life of the 
latter, to have at least increased the size of their shells con- 
siderably, if not indeed during their entire growth, is alone an 
almost insurmountable objection to such a conclusion. Doubt- 
less, like other marine sedentary animals, these mollusks, wh 
very young, floated freely about in the sea, until they found a 
during life. May they not, therefore, have been attracted to 
the bodies of Crinoids by the numerous little organisms 
brought in by the action of cilia, along the ambulacral furrows 
