vin EGHINODEEMATA— -MORPHOLOGY OF SKELETON 343 



Fio. 303.— Toxopneustes droebachiensis juv., 4 mm. in diam. 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 lb, lib, Ilia, 

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

 often not very evident. 



