Claxs 3. Echinoidea. 



135 



a small, smooth, wart-like elevation ; the largest knobs occur on the 

 imperforate interambulacral plates. The upper ends of the twenty- 

 rows of plates touch upon a circle of ten apical plates, five 







*-^ 







1 



B 



Fig. 89. Shell of a Eegular Sea-nrchin, Toxoptieustes Droebachiensis (young 

 speoimen, enlarged), from above (A) and from below (B). The radii are dark, g genital 

 plate, m madreporite, o ocular plate. In the middle of A is the anal area with the anus, — 

 Orig. 



Pig 90. Shell of an Irregular Sea-nrohin, Brissopsis lyrifera (young specimen, 

 enlarged), from above (4) and below (B). (The radii in A are not dark enough). 

 Posteriorly in A the anal area may be seen. The white bands are arese with very small 

 spines. — Orig. 



large and five small, with which they are immovably connected ; in 

 each inter-radius lies one of the larger, in each radius one of the 

 smaller plates. Bach of the larger plates is pierced by the opening 

 of a genital gland, and they are therefore termed the gen it a 



