Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
Genus 247. Triodiscus,[[286]] n. sp.
Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms closed by lattice-work and by an equatorial girdle.
The genus Triodiscus differs from the preceding Triopyle in the development of loose lattice-work on both sides of the discoidal shell. This network closes the gates and transforms the whole shell into a fenestrated lens. The singular species of Triodiscus correspond to certain species of Triopyle.
1. Triodiscus lenticula, n. sp.
Disk circular, lenticular, three times as broad as the central chamber. Three arm-chambers trapezoidal, of the same size and form as the three gates between them, which are closed by a loose delicate network (differs from Triopyle circulus by the production of the two convex latticed plates, which envelop the whole lens). Margin smooth.
Dimensions.—Diameter of the disk 0.045, of the gates 0.015.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
2. Triodiscus trigonus, n. sp.
Disk triangular, four times as broad as the central chamber. Three arm-chambers at the base half as broad, at the distal end twice as broad as the roundish gates. Surface smooth. On the three corners of the margin (in the arm-radius) three strong spines. (Differs from Triopyle trigona only in the loose framework closing the gates.)