Definition.—Thalassosphærida without alveoles, with numerous branched or compound spicula in the calymma.
The genus Thalassoxanthium differs from the foregoing Thalassosphæra, by the ramification of the spicula, and has therefore the same relation to it as Sphærozoum to Belonozoum. The soft unicellular body is as simple as in Actissa, and exhibits alveoles neither in the capsule nor in the calymma.
Subgenus 1. Thalassoxanthella, Haeckel.
Definition.—Spicula not geminate, but simply radiate, consisting of three, four, or more needles or shanks, radiating in different directions from one and the same point; shanks now simple or needle-like, now furcate or branched.
1. Thalassoxanthium triactinium, n. sp.
Spicula all (or nearly all) triradiate, composed of three (or sometimes in a few spicula four) needle-like shanks of equal length, diverging from one common point. Shanks straight or somewhat curved, smooth, pointed. Central capsule pellucid, twice as broad as its dark nucleus, without larger oil-globules. Jelly-envelope very thin, with numerous xanthellæ.
Dimensions.—Diameter of the central capsule 0.1, of its nucleus 0.05, length of the spicule-shanks 0.6 to 0.8.
Habitat.—Central Pacific, Station 266, surface.
2. Thalassoxanthium triradiatum, n. sp.
Spicula all (or nearly all) triradiate, composed of three (or sometimes in a few spicula four) needle-like shanks of different length, diverging from one common point. Shanks curved or bent, covered with small conical thorns. Central capsule dark, three times as large as the nucleus, with numerous large oil-globules. Jelly-envelope thick, without xanthellæ.