Xiphacantha foliosa, Haeckel, 1862, Monogr. d. Radiol., p. 385.
Spines lanceolate, tapering from the broader middle towards the two ends. From the middle part or from the outer third arise two opposite triangular apophyses, which are not perpendicular to the axis of the spine, but form an acute angle with its distal part. Therefore each spine represents a broad leaf with a middle rib and with three lobes or truncated teeth. The distal apex is distinguished by a violet colour. Base pyramidal, without leaf-cross. Central capsule yellow.
Dimensions.—Length of the spines 0.05 to 0.1, breadth 0.02 to 0.03.
Habitat.—Mediterranean, French shore, Saint Tropez, J. Müller.
Genus 327. Phractacantha,[[367]] Haeckel, 1881, Prodromus, p. 465.
Definition.—Astrolonchida with two branched, but not latticed, opposite apophyses on each radial spine.
The genus Phractacantha differs from its ancestral form, the preceding Lithophyllium by the ramification of the apophyses, which are either forked or bear lateral branches. If the prolonged fork-branches of the neighbouring spines meet and form a lattice-shell, this genus passes over into Phractaspis, the common ancestral form of the Diporaspida.
1. Phractacantha bifurca, n. sp.
Spines cylindrical, thin, of equal breadth throughout their whole length. Apex simple. Base pyramidal, without leaf-cross. From the outer third arise two opposite, thin, forked apophyses; ends of the fork branches acute.
Dimensions.—Length of the spines 0.1, breadth 0.006.