REPORT OF THE DIRECTOR I9IO 



249 



The greatest width of this specimen must have 



tional clearness, 

 been 13 mm. 



Plate arrangement. The following description of the plate 

 arrangement is based on the drawings here given and is further 

 aided by an examination 

 of the injured area of 

 Syntype A and the cross 

 section of the apotype. 



The circlet next the 

 stem consists of five, 

 similar pentagonal plates 

 which strongly suggest 

 the IBB of Crinoidea. 

 Above these and alter- 

 nating with them is 

 another circlet of five 

 plates. These are sep- 

 tagonal and suggest the 

 BB of Crinoidea. The 

 two aborad shoulders of 

 each of these plates rest 

 against the orad shoulders 

 of two plates of the first 

 circlet, while their ver- 

 tical shoulders meet each 

 other. There remain 

 three shoulders which lie 

 above their common ver- 

 tical sutures and the 

 uppermost of these is 

 horizontal. Resting on 

 each of these five hori- 

 zontal shoulders is a 

 vertical row of 3 or 4 

 hexagonal plates which 

 for convenience w^e may 

 for the present consider 

 as interradial in position. 

 Five other vertical rows of three or four hexagonal plates alternate 

 with the first rows mentioned and we may temporarily consider them 

 as radial in position. Each vertical row of the second series is sup- 



FiG. 24, 25 Palaeocystites dawsoni Billings. The 

 former a partial analysis of syntype B. The more distant 

 interradial plates of figure 24 are shaded and the position 

 of the food grooves indicated. 



It is to be understood that figure 25 shows but half or 

 one side of the conical and cylindrical portions of the theca 

 and that this lower figure is not intended to connect with 

 the upper. The two areas mapped may fail to meet in 

 some places and may overlap in others. The numbers 

 given the plates are simply for convenience in reference. 

 Numbers 55 and below belong to the figured plates of 

 syntype A and the numbers above 55 refer solely to 

 plates of syntype B. 



