Page:Scientific results HMS Challenger vol 18 part 2.djvu/281

Rh

Definition.— (vel Monocyrtida triradiata clausa) without internal columella and without apical horn.

The genus Archibursa has probably arisen from Peridium by loss of the apical horn, and is the only genus of Archiperida which bears no horn. The three basal feet are well-developed. It differs from the similar Tristylospyris by the absence of the sagittal ring and the corresponding longitudinal constriction.

1. Archibursa tripodiscus, n. sp. (Pl. 98, fig. 6).

Shell subspherical, smooth, with irregular roundish pores. Basal plate with three large triangular pores of equal size (fig. 6). Three feet widely divergent, straight, three-sided prismatic, about as long as the diameter of the shell.

Dimensions.—Diameter of the shell 0.07, length of the feet 0.09.

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

Archiphormida et Archiphænida, Haeckel, 1881, Prodromus, pp. 428, 429.

Definition.— multiradiata. ( with a simple, not jointed shell, resembling a simple cephalis, with numerous radial apophyses (four to nine or more).

The family, composed of the Archiphormida and Archiphænida of my Prodromus, comprises those in which the lattice-shell is quite without transverse constriction, but bears numerous radial apophyses. The two subfamilies differ in the shape of the basal mouth, which in the Archiphormida is a simple wide opening, but is closed in the Archiphænida by a lattice-plate.

Several Phænocalpida were formerly described by Ehrenberg, viz., Halicalyptra virginica (in 1844) and Litharachnium arachnodiscus (in 1872, called by him Carpocanium, though it is quite different from this genus, and closely allied to my Litharachnium tentorium, figured in 1862). These forms belong to the Archiphormida (with open mouth). Several fossil Archiphænida (with closed mouth) were figured by Ehrenberg, in 1875, as belonging to Petalospyris (ocellata, carinata, flabellum), though the absence of the sagittal ring and the corresponding longitudinal constriction demonstrates their character as Phænocalpis.