Plate XV. 



Fig. i. Ambulacral area of Echinus esculentus. l / l . 



2. Interambulacral area of Echinus acutus, var. norvegicus. 2 j l . 



3. affinis. z /,. 



4. elegans. 2 li. 



5. esculentus. I / I . 

 6. Apical area of Parechinus miliaris. 2 / I . 



7. Ambulacral area of Parechimis miliaris. 2 / I . 



8. microtitberculatus. 2 /i- 



9. Interambulacral area of Parechinus microtuberculatus. 2 / t . 



10. Ambulacral area of Echinus affinis. 2 / r (young specimen). 



ii. Interambulacral area of Parechinus miliaris. 2 j l . 



12. Apical area of Parechinus microtuberculattts. 2 / t . 



13. Ambulacral area of Echinus Alexandri. 2 / : . 



14. acutus, var. mediterranea. I / I . 



15. Interambulacral area of Echinus acutus, var. mediterranea. I / I . 



16. Ambulacral area of Echinus acutus, var. norvegicus. 2 / l . 



17. Interambulacral area of Echinus Alexandri. 2 /,. 



