Page:Scientific results HMS Challenger vol 18 part 1.djvu/326

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Definition.— with a double lattice-shell around every central capsule of the cœnobium; both concentric shells connected by irregular or subradial beams, commonly solid or lamellar staffs, rarely hollow tubes.

Definition.— with a double lattice-shell around every central capsule of the cœnobium; surface of the outer shell smooth.

The genus Clathrosphæra (with smooth surface) and the following Xanthiosphæra (with spiny surface) form together the small subfamily, Clathrosphærida, different from the other Collosphærida by the double lattice-shell. From the surface of the inner primary shell arise either solid spines or hollow tubes, which unite by the anastomosis of irregular branches and so form the outer secondary shell, often very incomplete and irregular. All Clathrosphærida seem to inhabit great depths.

Definition.—The connecting staffs between both shells are hollow tubes (derived from Siphonosphæra).

1. Clathrosphæra circumtexta, n. sp. (Pl. 8, fig. 6).

Inner shell spherical, with irregular roundish large meshes, now broader now smaller than their bars. Eight to ten meshes in the half meridian of the shell. All these meshes are prolonged into short cylindrical hollow tubes, about as long as broad, somewhat constricted in the middle. From the margins of the outer openings of these tubes proceed very numerous and delicate siliceous filaments, which all lie on the same spherical face, branch, anastomose, and twine over the openings and the intervals between them, forming a very thin, arachnoid spherical outer shell. The meshes of this are quite irregular polygonal, of very different size and form. The radius of the inner shell bears to that of the outer a ratio = 5 : 6.

Dimensions.—Diameter of the inner shell 0.11 to 0.13, of the outer 0.13 to 0.16; meshes of the inner shell 0.005 to 0.02, of the outer 0.005 to 0.04.

Habitat.—North Pacific, Stations 238 to 253, depths 2050 to 3950 fathoms.

Definition.—The connecting staffs between the two shells are solid rods or lamellar spines (derived from Acrosphæra).