Page:Scientific results HMS Challenger vol 18 part 2.djvu/208

1084 3. Pylospyris canariensis, n. sp. (Pl. 95, fig. 16).

Shell rough, with deep coronal and slight sagittal constriction. Galea hemispherical, with numerous small irregular, roundish pores, about half as long as the cephalis, with a slender conical horn of twice the length. Cephalis nut-shaped, with larger roundish pores of very unequal size, three pairs of larger pores on each side of the ring. Basal plate with two larger pores.

Dimensions.—Galea 0.03 long, 0.08 broad; cephalis 0.06 long, 0.11 broad.

Habitat.—North Atlantic, Canary Islands, surface.

Phormospyrida, Haeckel, 1881, Prodromus, p. 442.

Definition.— with a thorax, without galea; the shell composed of the bilocular cephalis and of a simple thorax arising from its basal face.

The family differs from the Zygospyrida, their ancestral group, in the development of a thorax, or a second fenestrated shell-joint, which arises from the lower face of the cephalis. It corresponds, therefore, to the Dicyrtida among the, and may perhaps be, wholly or partially, the ancestral group of the latter. When the sagittal ring and the longitudinal constriction of the cephalis disappear, the Phormospyrida pass over into the Dicyrtida.

Only three species of this family have been hitherto known, which were found fossil in Barbados, and described by Ehrenberg (1875) as Lithobotrys stiligera and Petalospyris confluens, and by Bütschli (1882) as Petalospyris anthocyrtoides. Fifteen other species are found in the Challenger collection, which we dispose here among five genera.

Two of these five genera (the horned Acrospyris and the hornless Phormospyris) possess the three typical basal feet of Cortina and Tripospyris, and may be derived from these genera by the development of network between the bases of the feet. The three other genera possess numerous feet, and may be derived in the same way from the Polyspyrida; the apical face differs in the three genera, in Desmospyris it is hornless, in Patagospyris it bears an apical horn, and in Rhodospyris three horns (an apical and two lateral or frontal).

The cephalis in the Phormospyrida exhibits the same typical structure, which we have described above, of all (compare, p. 1017). The thorax or the second joint of the shell arises by reticular connection of the bases of the basal feet, and represents a cylindrical or truncate-conical joint in the polypodal forms, or a three-sided joint in the tripodal forms. The terminal aperture or the mouth of the thorax is constantly open, and surrounded by the free ends of the feet.