Habitat.—Central Pacific, Stations 265 to 274, depths 2350 to 2925 fathoms.
Genus 213. Axodiscus,[[252]] n. sp.
Definition.—Porodiscida with a simple central chamber, surrounded by one single concentric ring, which is divided by radial beams into two to six or more radial chambers; margin of the disk armed with radial spines.
The genus Axodiscus differs from the preceding Archidiscus only in the shape of the margin of the small lenticular disk, which is armed with a variable number of radial spines, indicating certain axes or radii of the shell. If these marginal spines at certain equal distances from the margin branch and their distal ends become united by these branches forming a concentric second ring, the genus passes into Porodiscus. The different number and disposition of the marginal spines are probably very important, as determining the later development of two to four or more radii in the different genera of Porodiscida.
1. Axodiscus stylophorus, n. sp.
Ring circular, with two equal semicircular chambers, connected with the central chamber by two opposite radial beams, which are prolonged outside into two strong conical spines.
Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
2. Axodiscus triradiatus, n. sp.
Ring regular, triangular, equilateral, connected with the central chamber by three equidistant radial beams, which are prolonged outside into three short conical spines. (Differs from Archidiscus trioniscus in the possession of marginal spines.)