Cortical shell thin walled, with smooth surface and regular network. Proportion of both axes = 4 : 3. Pores circular, twice as broad as the bars; ten to twelve on the half equator. Medullary shell spherical, one-third as broad as the cortical shell. Polar spines strong, straight, cylindrical, with conical apex, as broad at the base as two pores; the larger once and a half to twice as long as the main axis, the smaller only one-third to one-fourth as long.
Dimensions.—Major axis 0.1 to 0.12, minor 0.08 to 0.09; pores 0.008, bars 0.004; diameter of the medullary shell 0.03; length of the larger polar spine 0.15 to 0.2, of the minor 0.04 to 0.05, basal thickness of them 0.02.
Habitat.—Cosmopolitan; Atlantic, Indian, and Pacific, surface.
4. Druppatractus testudo, Haeckel.
Stylosphæra testudo, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, Taf. viii. fig. 16.
Cortical shell thick walled, spindle-shaped, with smooth surface and regular network. Proportion of the two axes = 3 : 2. Pores circular, five times as broad as the bars; only six to seven on the half equator. Medullary shell ellipsoidal, about one-third as large as the cortical shell. Polar spines strong, short, three-sided pyramidal; the larger as long as half the transverse axis, the smaller only one-fourth as long.
Dimensions.—Major axis 0.12, minor 0.8; pores 0.015, bars 0.003; axes of the medullary shell 0.04 and 0.03; length of the larger polar spine 0.04, of the smaller 0.02, basal thickness 0.01.
Habitat.—Pacific, Philippine and Californian Sea (Ehrenberg), Stations 244, 266, 289, &c., depth 2550 to 2900 fathoms.
Subgenus 2. Druppatractylis, Haeckel.
Definition.—Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface thorny or papillose, covered with small conical spines or tubercles.