Page:Scientific results HMS Challenger vol 18 part 2.djvu/523

Rh 2. Cecryphalium sestrodiscus, n. sp. (Pl. 58, fig. 1).

Shell very flat, subconical, nearly discoidal, with two distinct strictures. Length of the three joints = 1 : 2 : 1, breadth = 1 : 8 : 10. Cephalis kidney-shaped, very small. Thorax flat, campanulate, with curved lateral outline; its pores irregular, polygonal, increasing in size towards the girdle. Abdomen horizontally expanded, like the brim of a hat, with five to six concentric, circular rows of pores, the pores of the inner rows twice to three times as large as those of the outer rows. (The inner circle of large, oblongish, quadrangular pores, characteristic of the preceding species, is here divided into three concentric rings by two circular hoops.)

Dimensions.—Length of the three joints, a 0.02, b 0.04, c 0.02; breadth, a 0.02, b 0.15, c 0.2.

Habitat.—Central Pacific, Station 274, surface.

Definition.— (vel Tricyrtida eradiata aperta) with conical abdomen, gradually dilated towards the wide open mouth. Cephalis with a single horn.

The genus Theoconus, and the following closely allied Lophoconus, differ from the other Theocorida in the conical or campanulate form of the shell; the abdomen is a truncated cone, gradually dilated towards the terminal mouth. The latter is usually truncated, widely open, sometimes with a slightly constricted peristome. The cephalis of Theoconus bears a single apical horn.

Definition.—Pores of the thorax and of the abdomen of nearly equal size and similar form.

1. Theoconus zancleus, Haeckel.

Eucyrtidium zancleum, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 41, Taf. vi. figs. 1-3.

Eucyrtidium zancleum, Haeckel, 1862, Monogr. d. Radiol., p. 321.

Shell bell-shaped, nearly conical, smooth. Length of the three joints = 1 : 3 : 4, breadth = 1 : 4 : 6. Cephalis nearly spherical, with a stout, straight, pyramidal horn of the same length. Thorax hemispherical. Abdomen gradually increasing in breadth towards the wide truncated mouth. Pores in all three joints nearly of the same shape, circular, regular, four times as broad as the thin bars.

Dimensions.—Length of the three joints, a 0.027, b 0.08, c 0.1; breadth, a 0.03, b 0.12, c 0.18.

Habitat.—Mediterranean (Messina, Naples, Nice, &c.).