NO. 184G. OX CERTAIN ELEUTHEROZOIC PELMATOZOA—KIRK. 7 



almost completely growii over. It is to be noted that the area 

 immediately surrounding the point of attaclmient is smooth and of 

 quite different appearance than the remainder of the theca. Again 

 in the case of figures 7, 8, wliich represents the base of another speci- 

 men of the same species, as well as in figures 9, 10, where the theca 

 was turned at somewhat of an angle to the plane of the area of attach- 

 ment, it may be seen that one side of the theca, wliich apparently 

 grew in contact ^dth some object, is quite smooth. In all these gen- 

 era mentioned, the area of attachment is large and well defined. 



It may be argued that Ecliinosphxra has a column of sufficient 

 length to raise the theca above the bottom and thus preclude the 

 possibility of contact phenomena and other features to be observed 

 in the genera cited above. Tliis argument is inadmissable, how- 

 ever, on various grounds. In the first place the sometimes extremely 

 excentric location of the fragment retained would not permit of such 

 support. Again the extremely small size of the pedicle compared to 

 that of the theca makes such an hypothesis quite untenable. 



Were a column to have been acquired by certain forms of EcMiv- 

 osphsera it could not have approached that possessed by Arachnocystis 

 in degree of speciahzation. These columns, as figured by Barrande 

 in the case of Arachnocystis infaustus, were never of any considerable 

 length, and apparently were never attached permanently to the 

 bottom. 



I tliink that one is justified in concluding that fixation did not 

 obtain in the adult stages of Echinosphsera, at least in the majorit}^ of 

 individuals. It seems probable that at some comparatively young 

 stage in the lives of the animals fixation by cementation took place. 

 Subsequently the cystids became detached. Occasionally fixation 

 may have persisted throughout Hfe. 



In connection wdth this apparent lack of consistent fixation in the 

 case of Echinosplisera must be considered the enormous range of the 

 genus. Originally described from the Baltic region, EcJiinospliaera 

 has been found throughout the United States from the Appalacliians 

 to the Rocky Mountains. Notwithstanding its great horizontal 

 range, its vertical range is very small, at least in the United States, 

 where it is restricted to a weU-defined zone. Moreover, as mentioned 

 above, the American species is probably specifically identical with 

 the Baltic. EcMnosphsera aurantium then has quite as great a range 

 as Uintacrinus socialis. Such wide distribution argues for a pelagic 

 habit, but one hesitates to apply this explanation to EcJiinosphsera. 



One may conceive perhaps that EcMnosphsera might have been a 

 floating organism. The extremely thin plates and consequent light- 

 ness of the animal might well indicate adaptation to such a form of 

 life. The globose theca likewise points in the same direction. The 

 specific gravity of certain Echinoderms is at no time so very much 



