Dimensions.—Diameter of the shell 0.32; larger aspinal pores 0.02, smaller 0.002 to 0.01; bars 0.003.
Habitat.—Indian Ocean (Madagascar), Rabbe, surface.
Subgenus 2. Icosaspidium, Haeckel.
Definition.—Condyles of the neighbouring plates grown together, and sutures obliterated; therefore the whole shell forms a single piece of acanthin.
7. Icosaspis tetragonopa, Haeckel.
Haliommatidium tetragonopum, Haeckel, 1862, Monogr. d. Radiol., p.421, Taf. xxii. fig. 13.
Parmal meshes all of nearly equal size and form, square, three times as broad as the bars, little larger than the sutural meshes. In each plate commonly sixteen equal square meshes, viz., four primary aspinal and twelve secondary, surrounding the former as a square corona. Radial spines tetrapterous, stout; the outer pyramidal half somewhat longer than the inner. This species differs from the similar Icosaspis tabulata (Pl. [136], fig. 2) in the concrescence of the sutures, the smaller number of pores, and the form of the stouter spines. The figure in my Monograph, drawn from a broken fragment, is not quite correct.
Dimensions.—Diameter of the shell 0.18, pores 0.009, bars 0.003.
Habitat.—Mediterranean (Messina, Corfu), surface.
8. Icosaspis icosahedra, n. sp.