Hapalosoma pellucidum (Agassiz, 1879). Adoral
and adapical ambulacral plating. From Mortensen, T. 1935. A
monograph of the Echinoidea. Volume 2, Bothriocidaroida,
Melonechinoida, Lepidocentroida and Stirodonta. C.A. Reitzel,
Copenhagen (fig. 149).