Page:Scientific results HMS Challenger vol 18 part 2.djvu/875

Rh dense fork-thicket. Whilst in Cœlotholus each frontal main tube (arising from the frontal corner of the galea at right and left) is divided into an anterior or pectoral, and a posterior or tergal style, in Cœlothamnus each of these two divergent main styles is again forked, so that the total number of projecting and radially diverging styles amounts to sixteen. One Mediterranean species of this genus, Cœlothamnus davidoffii, has been already described by Bütschli in 1882 (Zeitschr. f. wiss. Zool., vol. xxxvi. p. 486, Taf. xxxi.). Though its description on the whole is accurate, some important errors, which may be here corrected, are to be met with. The two central valves of the lattice-shell (dorsal and ventral) are symmetrically equal in size and in form, as in all other Cœlographida; the different forms and the inverse arrangement of the two valves, described by Bütschli (pp. 488, 491), were effected by an artificial dislocation and inversion. The peculiar opening, which, according to his opinion, was supposed to bring about a direct communication between the cavities of the galea and its valve, is in reality the optical section of the rhinocanna, the two convergent frenula of which he figured, but did not recognise. Cœlothamnus attains the greatest size among all Radiolaria; the diameter of the body in Cœlothamnus maximus amounts to 33 mm.

1. Cœlothamnus bivalvis, n. sp. (Pl. 122, figs. 6-9).

Sixteen styles all of equal length, about three times as long (in their free part) as the diameter of the dense fork-thicket. The size of the anchor-pencils tapers from the proximal to the distal end. Each of the four primary frontal tubes (which arise in opposite pairs from the frontal corners of the two galeæ) is twice forked, and so produces four styles.

Dimensions.—Diameter of the whole body 18, of the fork-thicket 2.4 to 3.0.

Habitat.—North Atlantic, Canary Islands, Station 354, surface.

2. Cœlothamnus davidoffii, Bütschli.

Cœlothamnus davidoffii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 486, Taf. xxxi.

Sixteen styles all of equal length (?), about four times as long (in their free part) as the diameter of the fork-thicket. The size of the anchor-pencils is nearly equal throughout their entire length. (Compare the careful description of this species by Bütschli.)

Dimensions.—Diameter of the whole body 15, of the fork-thicket 1.8.

Habitat.—Mediterranean (Villafranca, near Nice), Davidoff, surface.

3. Cœlothamnus sedecimalis, n. sp.

Sixteen styles straight, of different sizes. The pectoral or anterior branch of each frontal main tube is simple, and twice as long as the diameter of the large fork-thicket. The tergal or posterior branch is forked at the base, and its anterior branch is again forked in the middle part, so that three