Plate 54. 

 1-4. Arbacia punctiilata Gray. 



1. Young specimen 1.5 mm. iu diameter, seen from the abactinal side (same as PI. 53, 



figs. 6, 7, 8) ; Newport, 1872. 



2. Actinal system of specimen 3.G mm. in diameter, same as PI. 53, fig. 9; U. S. C. S. Gulf 



Stream Exp., 1868-69, off the Tortugas 125 fms. 



3. Abactinal part of odd anterior ambulacrum with adjoining genital plates and part 



of anal system, seen from the interior, same as fig. 2 and PI. 53, fig. 9. 



4. The abactinal system of a young specimen 2 mm. in diameter, showing the formation 



of the embryonic spines and ridges ; off the Tortugas 125 fms. 



5-6. Arbacia stellata Gray. 



5. Actinal plates of the odd ambulacrum and adjoining interarabulacrum of specimen 



16 mm. in diameter; "Hassler" Exp., Payta, Peru. 



6. The same as fig. 5, seen from the interior, showing the auricles and the primordial 



plate. 



