Plate XV. 



Ficr. i. Ambulacral area of Echinus esculentus. l l 1 . 



— 2. Interambulacral area of Echinus acutus, var. norvegicus. z /i- 

 _ 3. — - affinis. 2 /i- 



» 4. — — - — elegaus. 2 t . 



c _ — - — esculentus. I / I . 



— 6. Apical area of Parechinus miliaris. 2 j 1 . 



— 7. Ambulacral area of Parechinus miliaris. 2 /r 



8. — — - — microtuberculatus. 2 / t . 



— 9. Interambulacral area of Parechinus microtuberculatus. 2 / T . 



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



— 11. Interambulacral area of Parechinus miliaris. 2 /\. 



— 12. Apical area of Parechinus microtuberculatus. 2 j l . 



— 13. Ambulacral area of Echinus Alexandri. 2 / I . 



14, — — - — aczttus, var. mediterranea. I j 1 . 



— 15. Interambulacral area of Echinus acntits, var. mediterranea. l ,. 



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



— 17. Interambulacral area of Echinus Alexandri. 2 j 1 . 



