Dimensions.—Diameter of the shell 0.15, breadth of the peristome 0.15.
Habitat.—North-Western Pacific (south of Japan), Station 231, depth 2250 fathoms.
Genus 695. Challengeron, John Murray, 1879, in litteris et schedulis.
Definition.—Challengerida without pharynx, with one or more teeth on the mouth, and with marginal spines.
The genus Challengeron has in general the same shape as the preceding closely allied Challengeria, but differs from it in the development of radial spines on the sagittal margin of the shell, which in the latter genus is smooth. According to the different number and arrangement of these marginal spines, which give a very singular appearance to them, we divide the twenty-five species of this cosmopolitan genus into four subgenera:—(1) with a single, odd apical spine; (2) with two opposed aboral spines (a dorsal and a ventral); (3) with a bunch of aboral spines; (4) with numerous radial spines along the whole sagittal margin of the shell.
Subgenus 1. Challengeranium, Haeckel.
Definition.—Margin of the shell with a single spine on the apical pole, opposite to the peristome (Challengeriæ caudatæ).
1. Challengeron monodon, n. sp.
Shell subspherical, slightly compressed, with a single straight conical spine on the apical pole, about as long as the radius. Peristome with a single vertical, straight, conical tooth, diametrically opposite to the apical spine and of the same length. (Similar to Challengeria naresii.)
Dimensions.—Diameter of the shell 0.2 to 0.3, length of the two opposite spines 0.1 to 0.15.