NO. 1846. ON CERTAIN ELEUTHEROZOIG PELMATOZOA—KIRE. 57 



Crinoidea probably referable to Group I. — In the foregoing discussion 

 of the eleiitherozoic stalked crinoids only those forms have been cited 

 regarding wliicli there can be no question as to the vaUdity of the 

 asseveration. There are a number of genera, however, which we may 

 hold to have largely maintained a detached existence vnih almost as 

 much reason as in the forms described. Still it is only because of the 

 known association of a detached existence with certain structural 

 features that we may reasonably predicate a similar mode of life in the 

 case of the following genera. It A\dll be noted in these various types 

 that we have structures analogous to those that obtain in many of 

 the eleutherozoic crinoids hitherto described. 



Porocrinus. — Porocrinus is perhaps the most primitive type to be 

 considered in this collection. The notable breadth of the column in 

 its proximal portion and the marked rapidity with which it tapers 

 distad, together with the .comparative tenuity of its distal portion, 

 strongly indicates that we have here a column comparable to that 

 possessed by many of the detached cystids. In all probability we 

 may consider that the members of tliis genus led the existence of 

 vagile benthos and attached themselves at will by wTapping the 

 distal portion of the stem about some object. 



The Khodocrinidx. — In the case of the Rhodocrinidse we find at 

 least three genera in which we may well consider a detached existence 

 is largely maintained. In Rhodocrinus itself, as shown by the Kin- 

 derhook species where the columns are well preserved, the stem is 

 comparatively short and we may note a marked tendency toward 

 looping in its distal portion. In Acantliocrinus rex, as figured by 

 Jaekel (1895) we find the distal portion of the column coiled, which is 

 evidence that the stem was not firmly affixed to the bottom. It does 

 not seem improbable that the crinoid may well have been tem- 

 porarily attached by wrapping its column about some object. From 

 the size of the stem in this specimen one would scarcely think of it as 

 being prehensile, however. Jaekel lays considerable stress on tliis 

 coiling of the column, and uses it as one of the characters to differ- 

 entiate the genus from Rhodocrinus. As noted above, the feature 

 is probably quite as characteristic of Rhodoa^inus. In Diamenocrinus 

 jouani as figured by Oehlert (1891) the distal portion of the column is 

 represented as closely rolled into a coU consisting of at least three 

 volutions. This coil is in a single plane. As in the case of Acantho- 

 crinus, the column is of large size, and from the tightness of the coil 

 one might conceive that its function was rather in the nature of a 

 ballast or drag than a means of temporary attachment by looping 

 about some object. The same explanation may well apply to Acan- 

 thocrinus. From the remarkable similarity which we observe in 

 these three rather divergent genera as regards the coiHng of the 



