MOEPHOLOGICAL PAET. 49 



one, except in a very few cases. In the Hudson Eiver group of Cincin- 

 nati we occasionally find crinoidal disks, attached to pieces of coral, which 

 closely resemble the dorso-central of Antedon. These disks have a pit or 

 depression at the middle of the upper flice, sometimes enclosing a small 

 stem joint. They are irregularly round, and some of them have small pro- 

 cesses passing outward from the sides, which seem to represent primitive 

 cirri (Plate I. Figs. 9, 10). It is now worthy of note, that we find in 

 the same beds some remarkable crinoidal stems, with their lower ends wound 

 around some stem fragment or other object, almost as neatly as thread 

 upon a spool, the column gradually tapering as it coils, and becoming very 

 small at the end.=^ It has always seemed to us that these stems and the 

 terminal plates belonged together, and were separated during the life of the 

 Crinoid. Detached roots are found in considerable numbers at Burlington 

 and Waldron, and in almost every case the root parted from the stem a little 

 above the radicular cirri ; but it is curious that hardly ever are parts of 

 the crown found associated with them. From these facts we may infer that 

 the stem, at least in some cases, became detached from the root, so that the 

 Crinoid could change its place of attachment. A detachment of this kind 

 actually took place in a large number, if not in all, recent Pentacrinidse, as 

 shown by Sir Wyville Thomson,! P. H. Carpenter, and others. The former 

 describes this structure in Pentacrinus Wyville-Thomsoni as follows : " All the 

 stems of mature examples of this species end inferiorly in a nodal joint 

 surrounded by its whorls of cirri, which curve downwards into a kind of 

 grappling root. The lower surface of the terminal joint is in all smoothed 

 and rounded, evidently by absorption, showing that the animal had for long 

 been free. I have no doubt whatever that this character is constant in the 

 present species, and that the animal lives loosely rooted in the soft mud, 

 and can change its place at pleasure by swimming with its pinnated arms ; 

 that it is, in fact, intermediate in this, respect between the free genus 

 Antedon and the permanently fixed Crinoids." Carpenter found a number 

 of other species 0^ Pentacrinus, and some of Metacrinus, in the same condition. 

 Roots apparently of Pentacrinus, and belonging to mature or almost mature 

 specimens, are occasionally found on telegraph cables, but so far as we know, 

 minus the crown and main part of the stem ; and it is quite probable that 

 all Pentacrinidae were able to detach themselves and float about. 



* S. A. Miller : Journ. Cincin. Soc. Nat. Hist., Vol III. Plate 7, Fig. U. 

 t The Depths of the Sea, pp. 442-444. 



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