vin ECHINODERMATA MORPHOLOGY OF SKELETON 343 



IV 



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

 spread out in one plane (after Lov&n). B, Peristome plates. D, teeth. 



marked by common characters, and are distinguished from the plates I&, II&, Ilia, 

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

 often not very evident. 



