CLARK: CRINOID FAMILY PLICATOCRINIDAE 497 



the csdyx before the proximale has time to become attached; the 

 proximale therefore becomes pushed away from the calyx, but 

 exactly as in the case of the comatulids, cirri are protruded from 

 it, and it becomes united to the columnal just below it by a stem 

 syzygy, these two columnals now forming what is known as a nodal 

 and an infranodal, the nodal (with the cirri) being in origin a true 

 proximale, and the infranodal the columnal just beneath the true 

 proximale. Following the formation of this first nodal the pen- 

 tacrinite proceeds to grow an entirely new column, of which the 

 first nodal represents the terminal stem plate; this second column 

 grows to a definite length, and then the same nodal forming proc- 

 ess is repeated. Each pentacrinite nodal with the series of 

 internodals beneath it, therefore, is morphologically the equiva- 

 lent of the entire column in such types as the Apiocrinidae, Phryno- 

 crinidae, or the comatulids. 



In the adult pentacrinites only nodals are formed just beneath 

 the calyx, so that here we have a series of reduplicated proximales, 

 just as in the Apiocrinidae; but none of these nodals become at- 

 tached to the calyx, for they are constantly being pushed away 

 from the calyx by the formation of new nodals. At a Uttle dis- 

 tance from the calyx intercalated columnals begin to appear be- 

 tween them, with the nearest of which they always unite them- 

 selves by syzygy, so that at a somewhat greater distance from the 

 crown the nodals (proximales), united by syzygy to the infra- 

 nodals, with which they form syzygial pairs, become regularly 

 spaced, forming the typical pentacrinite column as we commonly 

 find it. 



In the bourgueticrinoid type of column any two of the colum- 

 nals may be united by stem syzygy; these double columnals are 

 rare in the distal portion of the column, but increase in frequency 

 toward the crown. Each of these syzygially united pairs of col- 

 umnals represents an effort to form a proximale which, thru 

 excessive stem growth, has been thrust away from the calyx 

 exactly as in the case of the pentacrinites. In addition to these 

 there is just under the crown a definite series of proximales, cor- 

 responding to the continuously growing and indefinite series found 

 in the pentacrinites. To emphasize the essential similarity of the 



