PART 5 FOREWORD XIII 



measurements and inserted them in the descriptions in the hope that they will assist 

 in comparisons with other material, and that their use will be adopted by othere in the 

 future to complement such measurements as the arm and cirrus length, already in use. 

 As for the illustrations to this part, it was decided that the inclusion of photo- 

 graphic plates is not justified for crinoids, more particularly for the almost uniformly 

 lO-armed Antedonidae, many of which are superficially quite similar. Instead, line 

 dra^vings have been substituted and these are supplemented by figures of species 

 given in parts 1 and 2 of this work, and included systematically in this final part. Apolo- 

 gies are due for the relative inversion of my figures of centrodorsals and calyces. In 

 drawing I tend to align comatulids wdtli the dorsal side uppermost and the centrodorsal 

 with its base towards the bottom, whereas Mr. Clark sees the whole oriented as in 

 life, with the centrodorsal downwards. 



distal 



interior exterior 



peripheral 



apical 



pos terio r 



Another confusion which I found on coming fresh to the study of crinoids lay in 

 the orientation of some of the terms used in description. 'Proximal' and 'distal' are 

 clear enough but 'anterior' and 'posterior' need some clarification for a radially sym- 

 metrical animal, particularly as Mr. Clark uses them in two distinct planes. One of 

 these is across the disl-c, the radius and corresponding arm or arms opposite the anal 

 interradius being anterior, while the other arms are right and left anterior or posterior. 

 The second plane extends along the lengths of all the arms, the tips being anterior. In 



