Definition.—Astrolonchida with twenty radial spines, each of which bears two opposite apophyses or lateral transverse processes; sometimes two longitudinal rows of opposite apophyses.
Genus 326. Lithophyllium,[[366]] J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 52.
Definition.—Astrolonchida with two simple, not branched, opposite apophyses on each radial spine.
The genus Lithophyllium was founded by J. Müller for a single species (Lithophyllium foliosum), which we also here retain as the type of the genus. It is the first observed Astrolonchid, which bears two opposite lateral apophyses on each spine, and may therefore be regarded as the ancestral form of the subfamily Phractacanthida. The two opposite apophyses are here simple, whilst in the other genera of the subfamily they are branched or multiplied.
1. Lithophyllium cruciatum, Haeckel.
Acanthometra cruciata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 49, Taf xi. fig. 11.
Xiphacantha cruciata, Haeckel, 1862, Monogr. d. Radiol., p. 385, Taf. xviii. fig. 13.
Spines cylindrical, very thin, crossed perpendicularly in the distal third by a thin transverse beam; both lateral rods of the cross have the same length as the distal end. Apex simple. Base pyramidal, without leaf-cross.
Dimensions.—Length of the spines 0.05 to 0.15, breadth 0.001 to 0.002.
Habitat.—Mediterranean, Atlantic, Stations 352 to 354, &c., surface.