﻿250 NEW YORK STATE MUSEUM 



ported on the horizontal shoulder of a separate pentagonal plate and 

 these five pentagonals are very similar in form and position to the 

 RR of the Rhodocrinidae. 1 The ten rows of hexagonal plates are 

 capped by a circlet of ten plates, five of which have become sep- 

 tagonal and the whole circlet supports fifteen smaller plates. The 

 regularity of the circlets of plates and the pentamerism of the 

 aborad two-thirds of the theca are now both lost. A partial circlet 

 of some three plates is introduced to the left of the anus and below 

 a peculiar pentagonal plate which lies next to an oral and a basal 

 arm plate. This pentagonal plate has a large central pore which 

 probably represents either the hydropore or the genital opening. 

 Passing orad we again meet with pentamerous symmetry in the 

 form of five rather circular basal arm plates or radials, and five 

 orals. The species thus has a theca composed of between 85 and 

 90 plates. 



Food grooves and pentamerous symmetry. The arm over the 

 anus and the two arms to the right of this each send a food groove 

 directly into the mouth by means of a short and straight passage 

 along the suture between two adjacent orals. The two remaining 

 food grooves are bordered by three orals and these grooves meet 

 each other before entering the mouth. 



It will be noticed that the orals, while five in number, are neither 

 symmetrical in form nor in radial arrangement. Pentamerous radial 

 symmetry is thus somewhat imperfectly expressed by the food 

 grooves, orals and basal arm plates. It is next wholly lost but is 

 present in great perfection in six or more circlets nearest the proxi- 

 mal stem point. In other words, pentamerism has here apparently 

 developed from two opposite poles and the aborad pole has attained 

 the greater perfection and extended its influence to the greater dis- 

 tance. It is not the intention here to call in question the theory 

 that pentamerous symmetry was due primarily to the bifurcation 

 of the two food grooves extended to the right and left of the hydro- 

 pore and anus in a primitive three-rayed form. We must not yet, 



1 In using a crinoid terminology in describing the aboral portion of the 

 theca, there has been no intention of implying that the plates of the first 

 circlet are really radial in position and lead to the unshaded plates or probable 

 radials of figure 24. The form may be monobasic or tribasic. The true rela- 

 tion of these plates might, however, be determined by additional work on 

 Syntype A. The borrowed terminology was used for convenience and to 

 emphasize the very perfect pentamerous symmetry found in the aboral region 

 of this species. 



