n. In the brachiopods of the superfamily Spiriferacea, either of two spirally coiled calcareous ribbons which support the brachia. These consist of two cones placed base to base or with their axes inclined to one another. The spiralia are usually joined by a transverse band or jugum the bifurcations from which may be produced between the volutions of the spiralia, thus forming a double spiral on each side, or diplospire.