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REPORT ON THE CRINOIDEA. 19 
condition as it occurs in Pentacrinus wyville-thomsoni. “All the stems of mature 
examples of this species end inferiorly in a nodal joint surrounded by its whorl 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.” 
Many other species of Pentacrinus and some of Metacrinus exhibit the same condition. 
It is best seen in Pentacrinus wyville-thomsoni, in which the nodal joint sometimes loses 
its ordinary characters altogether, becoming much enlarged and rounded below so as to 
be almost hemispherical in appearance (PI. XXII. fig. 27). In other cases, however, it 
retains its petaloid form and more or less of the small amount of sculpture which is 
usually found upon its lower face ; and a small rounded tubercle appears in the centre of 
the latter closing up the opening of its central canal. This is the usual condition of other 
species of Pentacrinus (e.g., Pentacrinus asteria, Pl. XI.) and of Metacrinus; and 
the analogy between it and the condition of a young Comatula just detached from 
its stem is very striking, as was pointed out by Sir Wyville Thomson.’ In both 
cases the severance takes place between a nodal joint and the top joint of the internode 
below it. 
The relations of the two longest stems that I have met with in this condition are 
shown as follows :— 
Pentacrinus decorus, stem 48 cm. long, rounded off at the thirtieth node. 
Metacrinus angulatus, stem 38°5 em. long, rounded off at the thirty-fifth 
node. 
With one exception (Pentacrinus maclearanus, Pl. XVI.) the three shortest of these 
semi-free stems that I have examined all belong to Pentacrinus alternicirrus. A, 47 mm. 
long, ends at the eleventh node; B, 49 mm., ends at the eleventh node; and ©, 55 mm., ends 
at the twelfth node. On the other hand, the smallest number of nodes in a semi-free stem 
oceurs in Pentacrinus wyville-thomsoni; one individual having a stem 90 mm. long, which 
1 The unusual enlargement of the lowest nodal joint in this individual suggests the idea that the structures which 
have been described by Hall under the name of Ancyrocrinus(Fifteenth Annual Report, New York State Cabinet of Natural 
History, 1862, pp. 89, 90) may be the detached stems of a Paleocrinoid in the semi-free condition. According to Hall they 
“have the form of a bulb or thickened column, with lateral ascending processes and a central ascending column of greater 
or less length ;” and he suggests that they “indicate the existence of a free floating Crinoid with the thickened bulb below 
serving as a balance for the column and body above. The articulating scar on the lower extremity of the smaller ones 
indicates that the animal was fixed in its young state.” The four lateral spine-like processes may very well have been 
cirri, the jointed structure of which has become obliterated by a calcareous overgrowth, just as in the lower part of the 
tetramerous stem. 
? Sea Lilies, p 10. 
