Plate 53. 

 1-9. Arbacia punctulata Gray. 



1. Young specimen immediately after the resorption of the pluteus, seen from the actinal 



side, 0.8 mm. iu diameter, including the spines. 



2. The same as fig. 1, seen from the abactiual side. The right posterior ambulacrum is at 



the top in figs. 1, 2. 



3. The same, seen in profile facing the left posterior interambulacrum. 



4. Large odd terminal tentacle of the right posterior ambulacrum of the same. 



5. The right posterior ambulacrum and part of the actinal system of the same; 1-5, 



Newport, 1900. 



6. The odd anterior ambulacrum of a specimen 1.5 mm. in diameter, seen from the actinilj 



side ; Newport, 1872. 



7. Ambulacral spine of odd anterior ambulacrum of same, seen in profile. 



8. Interambulacral spine of same, seen in profile. 



9. Abactinal system of young specimens 3.6 mm. in diameter; U. S. C. S. Gulf Stewaj 



Exj)., 18G8-69, 125 fms. off the Tortugas. 



