48 THE CKINOIDEA CAMEEATA OF NORTH AMEEICA. 



by Waclisrauth and Springer, and goes far to prove that the stem must 

 originally have had a far more intimate connection with the calyx than its 

 representatives of to-day have ; and the fact that in a number of Palseozoic 

 Crinoids the axial canal is very wide, compared with that of recent types, 

 seems to indicate an additional function to that of the axial canal, which, as 

 Neumayr suggests, we cannot explain from recent representatives." 



The apposed faces of the stem joints, with a few exceptions, are marked 

 by a series of more or less well defined angular ridges and alternating fur- 

 rows, which radiate from the opening of the central canal toward the dorsal 

 margin of the joints, but occasionally are restricted to their marginal por- 

 tions. The principal ridges alternate with smaller ones, w^hich do not extend 

 as far inward as the others, and all ridges of one joint meet corresponding 

 furrows of the apposed joint, which gives to the suture its serrated outline. 

 The faces of the joints are fiat, or slightly curved, the nodal ones having 

 sometimes a slight crest around the canal, which fits into a corresponding 

 depression of the apposed internodal. This indicates that the motion of the 

 stem was quite limited, and, as Carpenter remarks, " only of a passive char- 

 acter, due to the current of the water, etc., and independent of the will of 

 the animal." On coming in contact with other animals it was capable of 

 bending sideways, and of returning to its natural position when the obstruc- 

 tion was removed. 



In Platycrinus and Boiirgiieticrinus, in which the faces of the stem joints 

 are elliptic, their surfaces are provided with a well defined transverse ridge 

 following the long diameter of the joints, with- fossge at both sides, and 

 surrounded by a marginal reticulation. The ridges follow the twist of the 

 stem downward, admitting motion in all directions. In these families there 

 seems to have been a sort of rudimentary articulation between the suc- 

 cessive joints, while in the other families there was only a loose sutural 

 union. 



As to the habits of Crinoids, very little is yet known, even of the recent 

 ones. We know that in their pedunculate state the Comatulse were fixed 

 by means of a large plate, the so-called dorso-central ; and this led to the 

 belief that all Stalked Crinoids were permanently attached in a somewhat 

 similar manner. But this has never been satisfactorily proved, and, as we 

 know now, is not always the case with the recent Pentacrinidse. The distal 

 end in most Pal^ocrinoidea tapers rapidly and uniformly to a point, and the 

 terminal branches are given oiF from several joints, and not from a single 



