48 STUDIES IN THE DEVELOPMENT OF CRINOIDS. 



The first circle of cirri have been formed, situated radially as usual, attached 

 to the broad upper stalk-joint. The radials and costals have become much 

 broader and are about to assume their final shape. The orals are widely- 

 separated from the basals, lying in the middle of the disk, which has grown 

 very considerably. The anal plate remains small and is no longer contiguous 

 with the adjoining oral and radial. Along the sides of the arms some branched 

 spicules are seen; they represent the side-plates. The stalk has 24 joints, 

 which is evidently the normal number. They are slightly thickened at the 

 ends, those of the upper half of the stalk being the larger; upon the whole the 

 upper part of the stalk is distinctly stronger and more robust than the lower 

 part. The four upper joints are quite short and broadening towards the top 

 joint with the cirri, which is the broadest. Another specimen is slightly 

 more advanced in having 3 pinnules on each arm and the second whorl of 

 cirri beginning to develop, alternating with the first cirri, which are now fully 

 formed, with 14 joints, ending in a terminal claw. K. A. Andersson {op. cit., 

 p. 7) states that in the largest of the Pentacrinoids the pinnulse have begun 

 to develop, but the cirri have not yet appeared. Evidently he has failed 

 to see the largest specimens, in which the cirri are very distinct; I would 

 even be incUned to think that the specimen (taf. 2, figure 11) he represents 

 as the most advanced stage has no pinnules developed as yet; at least they are 

 not seen in the figure; apparently he has mistaken the tentacles for pinnules. 

 The developmental history of this species can not be traced any farther, 

 no very young free specimens being represented in the collection; but as no 

 further developed stages of Pentacrinoids are found, it seems probable that 

 they detach themselves soon after having reached the last-described stage. 



