104 PKOF. p. M. DUNCAN ON THE ANATOMY OF THE 



plate, not far from the aboral angle. This direction is that of the 

 suture of all the first plates of the triplets of the test placed at 

 and near the ambitus. 



The second plate is higher than the first at the interradial 

 suture, and is much the larger at the median line. Its abactinal 

 limit is the line of suture which separates it from the first plate, 

 and which has just been described. Its adoral limit is a small 

 part of tlie transverse suture between the compound plate under 

 consideration and that placed actinally. Then a line of suture 

 commences and passes from the transverse suture, aborally and 

 inwards with a low curved path, to reach the inner pore of the 

 plate number two. Thence the direction of the suture is 

 towards the median line, and slightly adorally, so that the 

 vertical suture is attained just aborally to the actinal angle of 

 the compound plate (fig. 8, I. 2). 



The third plate is much the smaller of the three : it includes the 

 most inwardly situated pair of pores of the triplet, and it reaches 

 the median line, being placed there adorally to the suture just 

 described ; but the plate does not come in contact with the inter- 

 radial suture. The actinal limit of this little plate is the 

 transverse suture between the two compound plates. 



The next compound plate (II.) closely resembles that just de- 

 scribed, but it is rather higher at the median line. The arrange- 

 ment of the sutures of the triplets is identical. Tlie pairs of 

 pores are, however, more remote from the interradial suture than 

 those of the compound plate already described. The obliquity 

 of the pores of the pairs in some instances prevents the satis- 

 factory use of the term adoral to indicate the inner pore of a 

 pair, for these may be placed aborally to the other series. 



Compound plate the third (III.) has the details of those already 

 described, but it is rather lower at the median line than the second 

 compound plate. Hence it is high externally, where, however, 

 there are only two plates of the triplet visible. Of these the 

 first is decidedly the smaller. The third plate is small, is well 

 removed from the interradial suture, and it reaches the median 

 line, resembling the third plates of the compound plates already 

 noticed. 



Further changes have been produced by pressure and growth 

 in the more actinally placed compound plates which are in 

 relation to the interradial plate situated actinally to the last 

 mentioned. 



