Subfamily 1. Triopylida, Haeckel

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers, which are separated by three notches or gates.

Genus 245. Triolena, n. gen.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms open.

The genus Triolena is the most simple form of all Pylodiscida, and must be regarded as their common ancestral form, from an ontogenetic as well as a phylogenetic point of view. The small shell is composed of a simple, spherical or lenticular, latticed, central chamber, and of three simple, surrounding equal arms, which are also simple latticed chambers, lie in the equatorial plane, and are separated by three equal angles or open gates.

1. Triolena primordialis, n. sp. (Pl. , fig. 12).

Arm-chambers trapezoid, nearly square, of the same size as the circular, lenticular, primordial, central chamber. Surface of the disk smooth.

Dimensions.—Diameter of the shell 0.045, of the central chamber 0.015, of each arm 0.015.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

2. Triolena tribelone, n. sp.

Arm-chambers lanceolate, of the same breadth as and twice the length of the triangular, central chamber; at the pointed end of each arm is a conical terminal spine (in the equatorial plane). Surface of the disk thorny.

Dimensions.—Diameter of the shell 0.05, of the central chamber 0.015; length of the arms 0.02, breadth 0.016.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Triolena trispinosa, n. sp.

Arm-chambers ovate, in the basal half nearly as broad as the hexagonal central chamber, at the pointed distal end with a strong conical radial spine of double the length. Surface rough.

Dimensions.—Diameter of the shell 0.055, of the central chamber 0.02.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

4. Triolena hexabelone, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the hexagonal central chamber, at the truncate distal end one and a half times as broad, and armed with two radial conical spines (in the equatorial plane). Surface of the disk smooth.

Dimensions.—Diameter of the shell 0.06, of the central chamber 0.02.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

5. Triolena trigonalis, n. sp.

Arm-chambers nearly triangular, at the base half as broad as the circular central chamber, at the concave lunulate distal end twice as broad, and armed with four conical radial spines (two on each side of the equatorial plane). Surface thorny.

Dimensions.—Diameter of the shell 0.05, of the central chamber 0.015.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Genus 246. Triopyle, Haeckel, 1881, Prodromus, p. 464.

Definition.—Pylodiscida with a simple, spherical or lenticular, central chamber, surrounded by three simple arm-chambers. Notches between the three arms transformed into gates by a connecting equatorial girdle.

The genus Triopyle differs from the preceding Triolene in the development of a simple ring or latticed equatorial girdle, which connects the distal ends of the three arm-chambers, and transforms the open notches between them into three gates. The ring may be circular, triangular, or hexagonal.

1. Triopyle circulus, n. sp.

Disk circular, three times as broad as the hexagonal central chamber. Three arm-chambers trapezoidal, at the convex distal end as broad, at the base half as broad as the three circular gates between them. Surface smooth. No marginal spines on the girdle.

Dimensions.—Diameter of the disk 0.045, of the gates 0.015.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

2. Triopyle hexagona, n. sp. (Pl. , fig. 13).

Disk hexagonal, three times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the truncated distal end as broad, at the base half as broad as the three triangular gates between them. Surface smooth. No marginal spines.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

3. Triopyle trigona, n. sp.

Disk triangular, four times as broad as the circular central chamber. Three arm-chambers nearly triangular, at the narrow base half as broad, at the distal end twice as broad as the circular or roundish gates. Surface smooth. On the margin (in the equatorial plane) three strong pyramidal spines (at the end of the arms).

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

Habitat.—Central Pacific, Station 274, depth 2750 fathoms.

4. Triopyle cordigera, n. sp.

Disk hexagonal, four times as broad as the hexagonal central chamber. Three arm-chambers triangular, at the base half as broad as at the truncated distal end, about the same size as the three heart-shaped gates. On the six corners of the margin (which forms a regular hexagon) are six pyramidal radial spines, as prolongations of the arm-edges.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—Indian Ocean, Ceylon, surface, Haeckel.

5. Triopyle renigera, n. sp.

Disk hexagonal, five times as broad as the circular central chamber. Three arm-chambers trapezoidal, at the base one-third, at the distal end two-thirds as broad as the three kidney-shaped gates. On the six corners of the margin (which forms an irregular hexagon) six conical radial spines, as prolongations of the arm-edges.

Dimensions.—Diameter of the disk 0.06, of the gates 0.02.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

6. Triopyle spinigera, n. sp.

Disk roundish, triangular, four times as broad as the triangular central chamber, which is armed with three radial spines between the arms. Arm-chambers club-shaped, at the narrow base one-fourth, at the distal end half as broad as the square gates. On the margin twelve large conical spines, two opposite on each face of the distal end of each arm-edge. Three smaller radial spines on the three corners of the girdle (in the same interradial meridian planes as the three spines of the central chamber). Compare Triodiscus spinosus.

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

Genus 247. Triodiscus, 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.)

Dimensions.—Diameter of the disk 0.04, of the gates 0.015.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

3. Triodiscus spinosus, n. sp. (Pl. , fig. 14).

Disk subcircular, four times as broad as the triangular central chamber. Three arm-chambers club-shaped, at the base one-third, at the distal end two-thirds as broad as the semicircular gates. Surface thorny. On the margin fifteen larger radial spines, three on the corners of the disk (in the radius of the gates), twelve on the two faces of the arms ends (two opposite on the edge of each end.) (Differs from Triopyle spinigera mainly by the delicate hexagonal network closing the gates.)

Dimensions.—Diameter of the disk 0.05, of the gates 0.02.

Habitat.—North Atlantic, Canary Islands (Lanzerote, Haeckel).