Parmal meshes hexagonal, ten to twelve times as broad as the thin bars, and on an average larger than the polygonal sutural meshes (the two proximal sides of each hexagonal parmal mesh two to three times as long as the four distal sides). Radial spines cylindrical, thin; their outer part longer than the inner.
Dimensions.—Diameter of the shell 0.15, of the parmal pores 0.01 to 0.015, bars 0.001.
Habitat.—North Pacific, Station 254, surface.
5. Tessaraspis trigonalis, n. sp.
Parmal meshes triangular, three to four times as broad as the thick bars, and on an average smaller than the irregular sutural meshes (in each plate all four parmal meshes of the same size, formed like an isosceles triangle, the distal base of which is somewhat curved, and convex towards the periphery, whilst the two proximal sides are straight). Radial spines thick, rounded; their outer conical part shorter than the inner cylindrical part.
Dimensions.—Diameter of the shell 0.1, of the parmal pores 0.01, of the sutural pores 0.01 to 0.02.
Habitat.—Tropical Atlantic (near Ascension), Station 345, depth 2010 fathoms.
6. Tessaraspis circularis, n. sp.
Parmal meshes circular, all eighty of equal size, quite regular, five to six times as broad as the thick bars, on an average larger than the roundish irregular sutural meshes. Radial spines quadrangular, prismatic, the outer part longer than the inner.
Dimensions.—Diameter of the shell 0.18, parmal pores 0.015 to 0.018, bars 0.003.