Page:Scientific results HMS Challenger vol 18 part 2.djvu/452

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Definition.— (vel Tricyrtida triradiata aperta) with three divergent solid ribs, which lie in the wall of the thorax and the abdomen, and are prolonged into three solid terminal feet.

The genus Theopodium and the following closely allied Pterocanium differ from the preceding four genera in the development of the three radial rods or the primary cortinar spines, which are not free lateral wings, but longitudinal ribs enclosed in the wall of the thorax and abdomen, and prolonged over the basal mouth into three free terminal feet. These are solid in Theopodium, which, therefore, corresponds to Lychnocanium among the Dicyrtida.

1. Theopodium tricostatum, n. sp. (Pl. 97, fig. 14).

Shell three-sided pyramidal, thorny, with two distinct strictures. Length of the three joints = 1 : 2 : 2, breadth = 1 : 3 : 4. Cephalis hemispherical, with a stout conical horn of the same length. Thorax with regular, circular, hexagonally-framed pores. Abdomen with irregular, roundish pores of very different sizes. From the middle part of the thorax arise the three prominent, wing-like edges of the pyramid, which are prolonged over its wide mouth into three stout, pyramidal, divergent feet about as long as the thorax, with dentate, lamellar edges.

Dimensions.—Length of the three joints, a 0.02, b 0.07, c 0.06; breadth, a 0.04, b 0.09, c 0.12.

Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.

2. Theopodium pyramidale, n. sp.

Shell three-sided pyramidal, rough, without external strictures, but with two broad internal girdles. Length of the three joints = 1 : 2 : 6, breadth = 2 : 4 : 8. Cephalis with a thick horn of the same length, conical. Thorax with very small, regular, circular pores. Abdomen with irregular, roundish pores of very different sizes. From the collar stricture arise the three rectilinear edges of the pyramid, which are prolonged over its wide-open mouth into three stout, divergent, pyramidal feet, about as long as the thorax.

Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.12; breadth, a 0.04, b 0.075, c 0.15.

Habitat.—Fossil in Barbados.

Definition.— (vel Tricyrtida triradiata aperta) with three divergent ribs, which run along the thorax and abdomen, and are prolonged into three latticed terminal feet.