of the branches of the radial spines. This outer shell is either a simple lattice-plate (comparable to the cortical shell of Diplosphæra), or a spongy framework (as in Rhizoplegma).
Subgenus 1. Oroplegmium, Haeckel.
Definition.—External shell a simple fenestrated lamella, forming an outer concentric lattice-sphere around the inner primary shell.
1. Oroplegma diplosphæra, n. sp. (Pl. 107, fig. 1).
Radial spines slender, cylindrical, smooth, more or less curved, about twice as broad as the smooth bars of the network. External shell a simple irregular lattice-sphere, with loose polygonal meshes, which are on an average three to four times as broad as the irregular meshes of the internal shell. The free prominent parts of the radial spines are irregularly branched, very long, with partly confluent branches.
Dimensions.—Diameter of the inner sphere 1.5 to 2.0, of the outer 2.5 to 3.0; length of the free spines 1.2, breadth 0.04.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Oroplegma spinulosum, n. sp.
Radial spines slender, cylindrical, thorny, more or less curved, very similar to those of the preceding species; the shell also much resembles that of Oroplegma perplexum. It differs from the latter in the more regular fenestration of both shells, and mainly in the shape of the bars and the spine-branches, which are all spinulate and densely studded with small conical thorns.
Dimensions.—Diameter of the inner sphere 1.5 to 2.0, of the outer 2.5 to 3.0; length of the spines 1.2, breadth 0.03.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
3. Oroplegma velatum, n. sp.
Radial spines stout, cylindrical, somewhat club-shaped, spiny, slightly curved, about three to four times as broad as the thorny bars of the network. External shell a simple lattice-sphere with irregular polygonal meshes, which are for the most part pentagonal and about four times as broad as the polygonal meshes of the inner shell. The free prominent parts of the radial spines are thickened, club-shaped, and about as long as the radius.
Dimensions.—Diameter of the inner sphere 2.0 to 2.4, of the outer 2.8 to 3.6; length of the free spines 0.5 to 0.7, breadth 0.12 to 0.15.
Habitat.—Tropical Atlantic, Station 338, depth 1990 fathoms.
