REPORT OF THE DIRECTOR I9IO 24! 



orad ends while l.ant.O and r.ant.O have widely truncated ends. 

 The openings between the orals to admit the visceral extensions of 

 the arms are relatively large, but orad of these the orals meet and 

 thus form a very solid or strong tegmen. The only evidence for 

 displacement to be found in this figure is the slightly disturbed 

 position of the upper edge of ant.R. 



The ambulacra pass over the edges of the orals and are small and 

 irregular. Still more irregular, and larger, are numerous interam- 

 bulacrals. These are best seen in plate 7, figure 2 above the madrc- 

 porite, but show also for l.post.R. 



The anal, X. The anal plate is fully as wide as the smaller 

 radials and we have therefore six subequal plates surrounding the 

 tegmen. This should make room for the development of a sixth 

 member of the orad radial series of b.vs. There seems to be evi- 

 dence for such a group, as may be seen by a study of the first three 

 figures of plate 6, but there is at the same time a concomitant and 

 marked weakening of the group which should have developed nor- 

 mally at the aboral angle of r.post.R. For instance, no b.vs. to 

 represent a group here have been added to the suture between 

 r.post.B and r.post.R. Cross sections of a few sutural canals can 

 be detected between RA and r. post. R, but they seem to be poorly 

 developed and of very small diameter. The group has but one 

 strong member to represent it and that is the oldest and 

 central b.v. on the suture between r.post.B and RA. It should 

 be noted that this b.v. represents the first formed of the series 

 whose initial position would have been at the aborad angle 

 of r.post.R and this position has been accorded it in text figure 3. 

 There seems to be evidence here that a branch from this group made 

 an early exit at the aborad angle of x and, by developing there, 

 practically stopped further development at the original position. If 

 we may so interpret the evidence, we have nothing to disturb the 

 fundamental pentamerism so clearly marked in all other places. 



If these groups of b.vs. were connected by subthecal canals which 

 in turn were connected with the circumoral canal of the water vas- 

 cular system and these canals should run so close to the under sur- 

 face of the thecal plates as to become attached to them, we should 

 find markings present so remarkably like the '' hydropJwres pal- 

 mccs '' which Barrandc discovered in Aristocystites, Pyrocystites 

 and Craternia that we must hesitate to accept Xeumayr's suggestion 



