8 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.41. 



greater than that of the surrounding medium, A decrease in the 

 weight of the animal, by a reduction of the amount of calcareous 

 matter to the minimum, and perhaps an increase in the buoyancy of 

 the organism, by an inconsiderable accumulation of gas within the 

 body would serve to reverse conditions. Movement of the brachial 

 appendages, however slight, would aid in sustaining the animal. 



If EcMnosj^hsera were indeed a floating organism, it could have been 

 transported these great distances by current action. Certainly one 

 would not expect the comparatively weak bracliioles to perform very 

 great service as organs of locomotion. Nor could the transportation 

 of the larvse alone account for the ^vdde dispersal of the species. If 

 we attribute such powers of dispersal to the larvae of EchinosjyJisera, 

 how may we well deny them to the young of closely related types? 

 It scarcely seems probable, though of course it is possible, that tliis 

 one genus should at that time have had larvae capable of such wide- 

 spread dissemination. No other cystids apparently have the range 

 of EcJiinosjplisera, as no doubt they would have, were larval distri- 

 bution the only factor. Furthermore, the fact that the projection 

 by wliich the animal was at one time attached is, in the adult speci- 

 mens, generally obscure and at times obsolete is positive evidence in 

 favor of a detached existence. That, subsequent to its detachment, 

 the animal did not remain passive is evidenced by the character 

 of the plates, which show no signs of the theca having rested upon 

 the bottom. It is possible that EchinospJisera may have crawled 

 on the bottom by means of its brachioles, but this is doubtful, to 

 say the least. The evident slenderness of the brachioles and their 

 probable lack of specialization indicate that they were not fitted to 

 function as ambulatory organs. 



Detachment in other many-plated Cystidea. — As we have seen, cer- 

 tain specimens of Aristocystis, Fungocystis and Craterina show clear 

 evidence of attachment to extraneous objects. Such an attachment 

 was not of universal occurrence, however, as an examination of Bar- 

 rande's (1887) figiires plainly shows. From the evidence afforded 

 by these figures one may postulate detachment of the organism, after 

 a period of fixation. Some of the figures indicate that fixation may 

 never have become effective, but one hesitates to draw such extreme 

 conclusions. 



As has been indicated above, a marked localized smoothing of the 

 plates and a complete covering of all pore structure may be noted 

 wherever definite fixation obtains. On the other hand, the presence 

 of pores opening outward may, I think, be held as indicating that 

 those plates bearing such pores were not in contact with some ex- 

 traneous object. It is held by Barrande and Bather that the open- 

 ings of these canals to the exterior were covered. Bather describes 

 this covering as probably a hard epidermis, but not a truly calcified 



