Page:Scientific results HMS Challenger vol 18 part 1.djvu/247

Rh Other forms were afterwards described by Müller and by myself in 1862. Further investigations have shown me that some species of this family are among the most common Radiolaria, and occur in astonishing numbers on the surface of all warmer seas. But the number of species is comparatively small, and their distinction is very difficult, as all the different forms are very variable and connected by intermediate forms—a truly "transformistic" group.

The only character sufficient for the constitution of genera in this transformistic group is found in the form and composition of the spicula; the very variable form of the jelly-calymma and the enclosed central capsule being without value for this purpose. But also the form of the spicula is very variable, and not always constant. In some species the particular form of the spicula is transmitted by constant heredity, whilst in others it is very inconstant, even in one and the same individual. (Compare the remarks on variability in the general introduction.)

As the number of various forms is rather great, it seems to be advisable to distinguish the three following genera.

Definition.— with simple needle-shaped spicula, which are neither radiate nor branched.

The genus Belonozoum comprises the Sphærozoida with simple needle-shaped spicula, and may be regarded as the colonial form of Thalassosphæra or Thalassoplancta, derived from these solitary by multiplication of the capsules and union in a common calymma.

1. Belonozoum bacillosum, n. sp.

Sphærozoum bacillosum, Haeckel, 1881, Manuscript.

Spicula all simple rods, straight cylindrical, obtuse at both ends, quite smooth. Central capsule pellucid, with one single central oil-globule.

Dimensions.—Diameter of the central capsule 0.08 to 0.12, length of the spicula 0.05 to 0.08.

Habitat.—Central Pacific, Station 271, surface.