Page:Scientific results HMS Challenger vol 18 part 1.djvu/244

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Definition.— with numerous large alveoles in the calymma (but not in the central capsule), and with numerous simple, needle-shaped spicula around the central capsule.

The genus Thalassoplancta was founded by me in 1862 for a Radiolarian with simple hollow needles in the calymma, which was afterwards recognised as a Phæodarium, belonging to Cannorrhaphis. We here retain this name for a true Thalassosphærid, very similar to the latter, but distinguished by the absence of the phæodium and the solid—not hollow—needle-shaped spicula, which are scattered in the alveolated calymma. Thalassoplancta can be regarded as the solitary form of the social Belonozoum.

1. Thalassoplancta longispicula, n. sp.

Spicula long and thin, cylindrical, smooth, more or less bent, pointed at both ends, similar to those of Thalassoplancta cavispicula. Central capsule thin-walled, without oil-globules, four times as broad as the nucleus, which encloses one single nucleolus.

Dimensions.—Diameter of the capsule 0.6, of the nucleus 0.15, of the calymma 4 mm.

Habitat.—North Atlantic, Færöe Channel (Gulf Stream), John Murray.

2. Thalassoplancta brevispicula, n. sp. (Pl. 2, fig. 2).

Lampoxanthium brevispiculum, Haeckel, 1882, Atlas.

Spicula short and thick, thorny, irregularly curved, pointed at both ends, very numerous. In the observed specimen all spicula were aggregated in the outer part of the voluminous calymma, whilst the inner alveolated part was devoid of them. Central capsule thick walled, with a layer of large oil-globules on its inner surface, twice as broad as the large nucleus which contains numerous nucleoli.

Dimensions.—Diameter of the central capsule 0.5, of the nucleus 0.2, of the calymma 2.5.

Habitat.—South Atlantic, Station 334, surface.

Definition.— with numerous large alveoles in the calymma (but not in the central capsule), and with numerous branched or compound spicula in the calymma.