3. Xiphoptera icosactena, n. sp.
Four equatorial spines about twice as long and four times as broad as the sixteen other spines. All twenty spines crossed in the outer third by two large opposite transverse apophyses, each of which bears on its distal side two to four branches perpendicular to the apophysis and parallel to the spine itself.
Dimensions.—Length of the four equatorial spines 0.26, of the sixteen smaller 0.11 to 0.14.
Habitat.—South Pacific, Station 288, surface.
Genus 340. Lithoptera,[[380]] J. Müller, 1858, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 155.
Definition.—Quadrilonchida with two opposite branched and latticed apophyses, either on each radial spine or only on a part of the twenty spines.
The genus Lithoptera, founded by Johannes Müller in 1858 for the first observed Mediterranean species, Lithoptera fenestrata, differs from all other Quadrilonchida in the fenestrated form of the apophyses, which he compared to the sails of a windmill. This peculiar fenestration is effected by two to four parallel pairs of opposite apophyses, which are crossed by perpendicular branches, parallel to the spine itself. Therefore the wings or lattice-plates have quadrangular meshes and lie in one meridian plane of the spine, not in a tangential plane (as in the Acanthophracta). Commonly the lateral ends of the four broad equatorial wings are so crossed that one lateral corner of each wing lies on the upper, the other corner on the under side of both its neighbours; but sometimes the meeting corners have grown together.
Subgenus 1. Lithopteranna, Haeckel.
Definition.—Four equatorial spines with transverse apophyses; sixteen others (eight tropical and eight polar spines) simple, without apophyses.
1. Lithoptera tetraptera, n. sp. (Pl. [131], fig. 9).