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three spines at the distal end are usually smaller than the others. 

 In the outer row there are nearly always two spines, occasionally 

 three for each plate, robust and prismatic in form, in the same 

 line with the outer row of adambulacral spines, and on the outer 

 side of the three most distal spines of the inner row, in close 

 contact with them. 



Ventrolaterals. — The ventrolateral plates themselves can not 

 be seen from the surface, since they are completely covered over 

 with flattened polygonal granules exactly similar to those of the 

 inferomarginals ; but the individual plates can be easily dis- 

 tinguished, being separated from one another by distinct 

 grooves. They are of different size and shape ; but a regular row 

 of them can be distinguished on either side of the ambulacral 

 fmTows, reaching out to the tip of the arms, but becoming rather 

 obscure towards the mouth. The plates of this series are rect- 

 angular in the middle part of the arms, but more or less roundish 

 or elliptical towards the mouth, and many of them bear one or 

 more, transversely elongated, valvate pedicellaria3. A second series 

 of ventrolateral plates of irregular size and shape can be recog- 

 nised in the arms, but this stops at some distance from the tip, 

 and becomes merged into the general ventrolateral system at the 

 base of the arms. Valvate pedicellarise may occasionally be present 

 on some of the plates of this series, but they are exceedingly 

 rare. In the interradial areas two more series, both more or less 

 ii-regular, are present outside the foregoing ; and the rest of the 

 interradial area is filled up with rounded or irregularly polygonal 

 plates without any regular arrangement. A few of these near 

 the mouth are usually larger than the others. Pedicellariae are 

 present on many of these plates (PI. XV, fig. 232). 



