40 PROCEEDINOS OF THE NATIONAL MUSEUM. vol. 41. 



up to 100 mm. in length, each columnal bearing a verticil. Although 

 a careful examination was made, no signs of attachment were shown 

 by the individuals. It would seem on the evidence of these writers 

 that P. hriareus and its allies have essentially the same column 

 structure, and that we may well postulate a similar habit for such 

 forms. 



Structure of Pentacrinus cirri. — The cirri in the case of these types 

 show special and peculiar modifications that are well worthy of more 

 than casual notice. For instance the cirri of Pentacrinus, as shown 

 by P. coUenoti, indicate a degree of specialization scarcely attained 

 by any other stalked genus. Figures of the cirri of this species as 

 given by de Loriol are here copied and given on Plate 5, figures 1-3. 

 It will be noted that a terminal claw has been developed, which in 

 itself is clearly indicative of a part of the functions of the cirri. The 

 shape of the constituent ossicles is of very great interest. Instead 

 of being round, they are considerably flattened. Each ossicle at its 

 outer margins has processes projecting backward and overlapping 

 the next preceding ossicle. There seems also to have been a less 

 pronounced process in the median line of each ossicle. These pro- 

 cesses and the type of articulation indicate great flexibility in a 

 vertical direction and slight possibilities of movement laterally. 



Function of Pentacrinus cirri. — The high degree of differentiation 

 exhibited by these cirri suggest that they may well be adapted to 

 function otherwise than simply to grasp objects. Indeed, a cirrus 

 wliich is circular or somewhat oval in section and equipped with a 

 terminal claw, would appear to have the optimum structure for such 

 purposes. The flattening of the cirri would be of no particular value 

 in perfecting them as grasping organs, and the very considerable 

 development of articular ridges and pits indicates a greater mobility 

 than would be developed were the cirri merely prehensile organs. 

 Bearing these facts in mind, the suggestion of de Loriol quoted above 

 relative to the part the cirri may have taken in effecting movement 

 does not seem wholly untenable. Considering the very considerable 

 development of cirri on one of these forms, both as to length and num- 

 ber, it is conceivable that even a slow movement of the cirri would 

 be of no little value in swimming, the action of the cirri tending to 

 elevate the crinoid. 



At first blush, it seems rather far-fetched, perhaps, to consider a 

 cirrus in any other light than as a prehensorium, Wlien one con- 

 siders, however, that in its natural medium the crinoid is practically 

 without weight, it will be seen that even a moderate lasliing motion 

 of the numerous long cirri would have a marked effect on the animal. 

 From the observations made by Agassiz (1888, vol. 2, p. 120), it 

 would appear that in the recent Isocrinus decorus the cirri are capable 

 of very considerable activity, it being stated that they move more 



