Puate 54. 
1-4, Arbacia punctulata Gray. 
. Young specimen 1.5 mm. in diameter, seen from the abactinal side (same as PI. 55, 
figs. 6, 7, 8); Newport, 1872. 
. Actinal system of specimen 3.6 mm. in diameter, same as Pl. 53, fig.9; U.S. C. 8. Gulf 
Stream Exp., 1868-69, off the Tortugas 125 fms. 
. Abactinal part of odd anterior ambulacrum with adjoining genital plates and part 
of anal system, seen from the interior, same as fig. 2 and Pl. 53, fig. 9. 
. The abactinal system of a young specimen 2 mm. in diameter, showing the formation 
y 4) g§ Sp 9 g 
of the embryonic spines and ridges; off the Tortugas 125 fms. 
5-6. Arbacia stellata Gray. 
. Actinal plates of the odd ambulacrum and adjoining interambulacrum of specimen 
16 mm. in diameter; “Hassler” Exp., Payta, Peru. 
. The same as fig. 5, seen from the interior, showing the auricles and the primordial 
plate. 
/ 
