Page:Scientific results HMS Challenger vol 18 part 2.djvu/108

984. Basal ring smaller than the sagittal ring, thorny, kidney-shaped, with four different gates; the two cardinal pores much larger than the two jugular pores. (The four basal pores are often much larger than in the specimen figured by Bütschli. Also the number, form, and size of the spines is very variable.)

Dimensions.—Height of the frontal ring 0.07 to 0.09, breadth 0.17 to 0.2.

Habitat.—Fossil in Barbados.

Definition.—Sagittal and frontal ring of equal size and form.

4. Tristephanium quadricorne, n. sp. (Pl. 93, fig. 7).

Sagittal and frontal ring of equal size and form, larger than the circular basal ring. From the four corners, in which the latter crosses the two former, arise four strong, divergent spines, branched like a deer's antler. Some smaller spines are scattered on the rings, and a bunch of four spines arises on the apical pole. The four upper gates are triangular, the four lower nearly semicircular, the latter of equal size, half as large as the former.

Dimensions.—Height of the frontal ring 0.13, breadth 0.14.

Habitat.—South Atlantic, Station 342, depth 1445 fathoms.

Definition.— with eight large, partly fenestrated gates; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three latticed complete rings, perpendicular to one another.

The genus Tricyclidium differs from the preceding Tristephanium, its ancestral form, in the development of loose rudimentary lattice-work along the rings, and therefore bears to it the same relation that Plectocoronis does to Eucoronis. It may pass directly over into Dictyospyris.

1. Tricyclidium dictyospyris, n. sp. (Pl. 93, fig. 13).

Sagittal ring ovate, twice as thick as the two other larger rings, which become very thin, thread-like at the lateral junction, and are both slightly violin-shaped, in the middle sagittal plane constricted; the frontal ring larger than the basal. All three rings bear small scattered spines, which are irregularly branched, and by anastomoses of the thread-like branches form small irregular meshes along the rings. The four basal gates are of equal size.

Dimensions.—Height of the frontal ring 0.11, breadth 0.15.

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