Page:Scientific results HMS Challenger vol 18 part 2.djvu/440

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Definition.— (vel Tricyrtida triradiata aperta) with three simple, free lateral wings arising from the sides of the thorax.

The genus Pterocorys, comprising numerous and some very common species, may be one of the oldest and most primitive Theopilida, and is perhaps the common ancestral form of all Tricyrtida. It exhibits three free lateral wings, arising from the sides of the thorax, like Lithomelissa among the Dicyrtida, and may be derived directly from this genus by development of an abdomen. The latter is commonly cylindrical or ovate, with a wide open mouth, whilst the thorax is either campanulate or three-sided and pyramidal.

Definition.—Horn of the cephalis simple. Abdomen not prolonged into a narrow tube.

1. Pterocorys campanula, n. sp. (Pl. 71, fig. 3).

Shell campanulate, with two distinct strictures. Length of the three joints = 2 : 3 : 2, breadth = 2 : 4 : 6. Cephalis subovate, with a pyramidal horn of the same length. Thorax subconical, in the middle zone with three conical, horizontal wings, shorter than the cephalis, from which three thin ribs are decurrent to the mouth. Abdomen short and much dilated, with wide, truncate mouth. Pores nearly equal, small, subregular, circular.

Dimensions.—Length of the three joints, a 0.04, b 0.06, c 0.04; breadth, a 0.03, b 0.08, c 0.12.

Habitat.—Central Pacific, Stations 266 to 274, surface.

2. Pterocorys carinata, Haeckel.

Eucyrtidium carinatum, Haeckel, 1862, Monogr. d. Radiol., p. 322, Taf. vii. figs. 4-7.

Shell subovate, with two distinct strictures. Length of the three joints = 1 : 2 : 3, breadth = 1 : 3 : 4. Cephalis ovate, with a pyramidal horn of twice the length. Thorax campanulate, with three decurrent crests, from which in the lower part three small conical wings arise, shorter than the cephalis. Abdomen barrel-shaped, inflated, with wide, truncate mouth. Pores everywhere equal, small, regular, circular, quincuncial.

Dimensions.—Length of the three joints, a 0.25, b 0.05, c 0.075; breadth, a 0.25, b 0.09, c 0.1.

Habitat.—Cosmopolitan; Mediterranean, Atlantic, Pacific; many stations, surface.