Page:Scientific results HMS Challenger vol 18 part 2.djvu/196

1072

Definition.— apoda, without descending basal feet.

Definition.— without basal feet, with an apical horn.

The genus Circospyris and the following closely allied genus Dictyospyris represent together the small subfamily Circospyrida, differing from all other Zygospyrida in the absence of feet on the basal face. They have probably arisen from the Tripospyrida (Tripospyris) by reduction and loss of the feet (in the same way as the eradiate from the triradiate). But it is also possible that many of the Circospyrida (if not all) are derived directly from the Semantida (Clathrocircus) by the closing of the two lateral openings and by completing the framework.

1. Circospyris nucula, n. sp. (Pl. 95, fig. 13).

Shell nut-shaped, compressed, smooth, with prominent sagittal ring. On each side of the ring three to four pairs of very large annular polygonal pores. Lateral pores small and numerous, roundish. Basal plate with two large pores only. Horn slender, conical, shorter than half the shell.

Dimensions.—Shell 0.11 long, 0.13 broad.

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

2. Circospyris gigas, Haeckel.

Dictyospyris gigas, Ehrenberg, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 68, Taf. xix. fig. 6.

Shell nut-shaped, tuberculate, with distinct sagittal stricture. On each side of the ring four pairs of larger annular pores. Lateral pores roundish, smaller. Basal plate with four large central and a circle of eight to twelve smaller peripheral pores. Horn cylindrical, about half as long as the shell (in the inverted figure of Ehrenberg directed downwards).

Dimensions.—Shell 0.1 to 0.15 long, 0.15 to 0.2 broad; horn 0.05 to 0.08 long.

Habitat.—Fossil in Barbados.

3. Circospyris tridentata, Haeckel.

Dictyospyris tridentata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 70, Taf. xix. fig. 10, a, b.

Shell nut-shaped, smooth, with sharp sagittal stricture. On each side of the ring two pairs of large annular pores. Lateral pores roundish, smaller. Basal plate with six large pores. Horn slender, cylindrical, about as long as the shell, with three sharp teeth at the distal end.

Dimensions.—Shell 0.03 long, 0.05 broad; horn 0.03 long.

Habitat.—Fossil in Barbados.