NO. 1846. ON CERTAIN ELEVTUEROZOIC PELMATOZOA—KIRK. 17 



noted that this is one of the few genera to which an eleutherozoic 

 habit has been ascribed by former writers. The column is of the 

 type given as characterisitic of the members of this group, and there 

 is no evidence of fixation. In addition to the figures given in various 

 pubhcations I have personally examined and collected a considerable 

 number of beautifully preserved specimens referable to this genus, 

 and in no case have found any evidence of a terminal plate or other 

 structural modification for purposes of attachment. The column is 

 in many instances remarkably short, scarcely exceeding the length 

 of the theca. Probably in no case was it of more than twice the 

 length of the theca. It tapers quite rapidly, and gives evidence of 

 having been unusually flexible. 



In Ghjptocystis the negative evidence of the lack of special adapta- 

 tion to a prostrate mode of hfe points strongly to the conclusion that 

 in this genus an erect position was constantly maintained. This fact 

 argues against the derivation of Ghjptocystis from CTieirocrinus as 

 has been suggested by Jaekel, inasmuch as in the latter genus are 

 to be noted marked modifications pointing to the assumption of a 

 prostrate habit. 



Lepadocrinus. — The genus Lepadocrinus with its curious column is 

 worthy of special mention in connection with this group. In this 

 genus a considerable number of the distal columnals are fused to 

 form an elongate subcylindrical body. (PI. 5, figs. 6, 7.) There are 

 no signs of cirri, and the distal end of the column is smoothly rounded 

 off. Subsequent to the fusion of the columnals there was a secondary 

 deposition of stereom, causing a marked enlargement of this portion 

 of the column. The resemblance of this fused portion, barring the 

 lack of modified cirri, to " Ancyrocrinus'^ is woi'thy of note. It 

 seems quite possible that in this instance, as in the case of the crinoid, 

 the fused appendage served as ballast or as a drag. It may be that 

 the distal portion of the column in Lepadocrinus was buried in soft 

 mud, but if such were the case fixation must have been of a most 

 precarious sort. Attachment by cementation apparently never 

 took place. It is of particular interest to note an eleutherozoic habit 

 in the case of Lepadocrinus, inasmuch as this was the last known 

 representative of the erect, stalked Cystidea. 



Evidence of a prostrate Jidbit in type 2. — In many of the genera prob- 

 ably referable to this group we know little or nothing regarding 

 the structure of the column. Owing to this fact we may not with 

 certainty ascribe an eleutherozoic habit to them. It is not until we 

 come to treat of those forms in which the modifications incident 

 to the assumption of a prostrate existence become manifest that we 

 may safely postulate a free existence from the evidence afforded by 

 the theca alone. These changes are, if well developed, unmistakable 

 and of necessity infallibly point to a detached existence. 

 94428°— Proc.N.M. vol.41— 11 2 



