Page:Scientific results HMS Challenger vol 18 part 2.djvu/393

Rh

Definition.— (vel Dicyrtida multiradiata aperta) without thoracic ribs, with nine terminal feet around the mouth. Cephalis free, with an apical horn.

The genus Anthocyrtis (in the original definition of Ehrenberg) contained all Dicyrtida without thoracic ribs, with terminal feet. We here restrict the definition to those Sethophormida in which the number of free terminal feet is constantly nine (three primary perradial and three alternate pairs of secondary interradial feet). Anthocyrtis may be derived either directly from Patagospyris by loss of the sagittal ring, or from Lychnocanium by interpolation of three secondary feet.

Definition.—Feet of the peristome-corona divergent, their basal distance less than their terminal distance.

1. Anthocyrtis mespilus, Ehrenberg.

Anthocyrtis mespilus, Ehrenberg, 1854, Taf. xxxvi. fig. 13; Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, p. 66, Taf. vi. fig. 4 (not 5).

Shell smooth, with distinct collar stricture. Length of the two joints = 1 : 5, breadth = 2 : 6. Cephalis hemispherical, with a stout pyramidal horn of twice the length. Thorax nearly hemispherical, with regular, circular, quincuncial pores. Mouth scarcely constricted, with nine divergent, triangular, lamellar feet, about as long as the thorax.

Dimensions.—Cephalis 0.012 long, 0.02 broad; thorax 0.05 long, 0.06 broad.

Habitat.—Fossil in Barbados.

2. Anthocyrtis furcata, Ehrenberg.

Anthocyrtis furcata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 64, Taf. vi. fig. 2.

Shell smooth, with deep collar stricture. Length of the two joints = 1 : 5, breadth = 2 : 6. Cephalis hemispherical, with a short pyramidal horn of half the length. Thorax hemispherical, with large, irregular, roundish pores. Mouth scarcely constricted, with nine divergent, curved, slender feet, which are about as long as the shell, and forked at the distal end.

Dimensions.—Cephalis 0.01 long, 0.02 broad; thorax 0.05 long, 0.06 broad.

Habitat.—Fossil in Barbados.