Page:Scientific results HMS Challenger vol 18 part 2.djvu/99

Rh in the figure seen from the apical pole) with cylindrical rods, armed with numerous stout spines, branched like a deer's antler. Basal gate rather oblong, twice as broad as long.

Dimensions.—Height of the frontal ring 0.08, breadth 0.16.

Habitat.—Central Pacific, Station 272, depth 2600 fathoms.

4. Coronidium acacia, n. sp. (Pl. 82, fig. 2).

Frontal ring and sagittal ring nearly circular, of equal size, truncated at the base. Basal ring circular, somewhat smaller. All three rings with prominent edges, bearing bunches of short and straight pointed spines, like those of an Acacia. Basal gate circular.

Dimensions.—Height of the frontal ring 0.12, breadth 0.14.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

Akad. d. Wiss. Berlin, p. 485.

Definition.— with five large, partly latticed gates (four lateral and one basal). Skeleton composed of two incomplete, partly fenestrated meridional rings, and one complete basal ring.

The genus Acanthodesmia, the oldest known form of all Coronida, differs from the preceding Coronidium, its ancestral form, in the development of irregular loose lattice-work along the rings, and therefore bears to it the same relation that Zygostephanium does to Zygostephanus. The first species described by Johannes Müller, Acanthodesmia vinculata ("with five large gates between the bars of the shell") remains the true type of this genus; the second species described by him (Acanthodesmia dumetum) belongs to the Plectanida (Polyplecta).

1. Acanthodesmia vinculata, J. Müller.

Acanthodesmia vinculata, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 30, Taf. i. figs. 4-6 (non 7).

Lithocircus vinculatus, J. Müller, 1856, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 484.

Frontal ring violin-shaped, one and a half times as broad as high, with a sagittal constriction. Sagittal ring ovate, smaller. The four gates between the two rings are partly fenestrated by a few thin threads, irregularly branched and connecting the two rings. A few short thorns are scattered here and there. Basal gate elliptical.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—Mediterranean (Nice), Atlantic (Canary Islands), surface.