Genus 233. Stauralastrum,[[272]] n. gen.
Definition.—Porodiscida with four simple, undivided, chambered arms, without a patagium; quadrangular shell a regular cross, with four equal arms placed at right angles.
The genus Stauralastrum is the most simple form of the Tessarastrida, or of those Porodiscida in which the margin of the central disk is armed with four chambered arms. In Stauralastrum these four arms are quite simple and equal, without a patagium, separated by four right angles, so that the whole shell represents a regular rectangular cross. If we connect the distal points of the arms by lines, we get a complete square. (In my Prodromus, 1881, the species of this genus were united with Hagiastrum, which genus I now retain for the simple bilateral Tessarastrida.)
Subgenus 1. Stauralastrella, Haeckel.
Definition.—Ends of the arms blunt, without terminal spines.
1. Stauralastrum cruciforme, n. sp. (Pl. [45], fig. 6).
Arms very thin, nearly linear, four to five times as long as broad, of equal breadth at the base and at the truncated distal end; their breadth equals one-third of the radius of the central disk. Edges of the arms parallel.
Dimensions.—Radius of each arm 0.8, breadth 0.016.
Habitat.—South Pacific, Station 293, surface.
2. Stauralastrum lanceolatum, n. sp.