vm ECHINODERMATA MORPHOLOGY OF SKELETON 343 



IV 



FIG. 303. Toxopneustes drcebachiensis juv., 4 mm. in diam. The whole system of plates 

 spread out in one plane (after Loven). B, Peristome plates. D, teeth. 



marked by common characters, and are distinguished from the plates Ib, lib, Ilia, 

 IVb, Va, which also resemble one another. These different characters are, it is true, 

 often not very evident. 



