5. Stylatractus carduus, Haeckel.
Cortical shell thin walled, spiny, with regular, circular pores, five times as broad as the bars; ten to twelve on the half equator. Polar spines conical, half as long as the main axis, at the base broader than the pores. (The cortical shell is ellipsoidal as well as both medullary shells; the figure of Ehrenberg, as is generally the case, is more correct than his description. This interesting species occurs in the Barbados rocks, with double as well as with simple medullary shell, and may in the latter case be distinguished as Lithatractus carduelis.)
Dimensions.—Major axis of the cortical shell 0.12 to 0.16, minor 0.1 to 0.14; pores 0.01 to 0.02, bars 0.002 to 0.005; main axes of the ellipsoidal medullary shells 0.05 and 0.03; length of the polar spines 0.06, basal breadth 0.02.
Habitat.—Fossil in the Tertiary rocks of Barbados.
Subgenus 3. Stylatractona, Haeckel.
Definition.—Network of the outer shell irregular, with meshes of different size or form; surface smooth, without thorns or papillæ.
6. Stylatractus variabilis, n. sp.
Cortical shell thin walled, smooth, with irregular, roundish pores, twice to six times as broad as the bars; twelve to sixteen on the half equator. Polar spines conical, about half as long as the main axis, and as broad at the base as the inner medullary shell. (The size and form of the pores and of the polar spines in this species are very variable, so that the proportions given are to be understood as averages.)
Dimensions.—Major axis 0.13, minor axis 0.11; pores 0.004 to 0.012, bars 0.002; main axes of the ellipsoidal medullary shells 0.07 and 0.04; length of the polar spines 0.06, basal breadth 0.03.
Habitat.—Pacific, central area. Stations 272 to 274, depth 2350 to 2750 fathoms.
7. Stylatractus sethoporus, n. sp. (Pl. 17, figs. 2, 3).
Cortical shell thick walled, smooth, with large irregular, roundish pores, twice to four times as broad as the bars; seven to eight on the half equator. At the bottom of each pore a thin lamella of silex, perforated by four to six irregular, roundish, double-contoured porules. Medullary shells resemble those of Stylatractus giganteus. Polar spines three-sided pyramidal; their length and basal thickness scarcely equal the diameter of the inner medullary shell.
Dimensions.—Major axis 0.15, minor axis 0.13; pores 0.02, bars 0.005, porules 0.01; length of the polar spines 0.04.
Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.
