REPORT ON THE CRINOIDEA. 19 



condition as it occurs in Pentacriniis loyville-thomsoni. " All the steins 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 Ions 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 wdth 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 Pentaerinus and some of Metacrimis exhibit the same condition. 

 It is best seen in Pentaerinus ivyville-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. 17)} 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 Pentaerinus {e.g., Pentaerinus asteria, PI. XL) and of Metacrimis ; 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 : — 



Pentaerinus decorus, stem 48 cm. long, rounded ofi"at the thirtieth node. 

 Metacrinus angulatus, stem 3 8 '5 cm. long, rounded ofi" at the thirty-fifth 

 node. 



With one exception {Pentaerinus maclearanus, PL XVI.) the three shortest of these 

 semi-free stems that I have examined all belong to Pentaerinus alternieirrus. A, 47 mm. 

 long, ends at the eleventh node ; B, 49 mm., ends at the eleventh node ; and C, 55 mm., ends 

 at the twelfth node. On the other hand, the smallest number of nodes in a semi-free stem 

 occurs in Pentaerinus 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 nameof ^7ic!/rocnnMs(Fifteenth Annual Report, New York State Cabinet of Natural 

 History, 1862, pp. 89, 90) may be the detached stems of a Palseocrinoid in the semi-free condition. According to HaU 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 yoimg 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. 



