spine, placed in the prolongation of the main axis, and about half as long as the shell. Its base is pierced by two large opposite pedal pores. The anterior or oral pole bears a cylindrical peristome, similar to a bird's head, and curved towards the ventral face; on both sides of its neck (at right and left) a series of three or four irregular, ovate, buccal holes. The neck bears four cylindrical, spinulate, radial tubes (two on each side), crossed nearly horizontally, and placed in two diagonal planes perpendicular one to another; these planes correspond to those in which the four feet of Tuscarusa medusa lie. The base of each tube is pierced by four dental pores.
Dimensions.—Length of the shell 3.2, breadth 1.6.
Habitat.—North Pacific, Station 250, depth 3050 fathoms.
2. Tuscaridium lithornithium, n. sp. (Pl. 100, figs. 8, 8a, 8b).
Shell spindle-shaped, twice as long as broad, very similar to the preceding closely allied species. It differs from the latter in the following characters:—The curved proboscis of the peristome is broader and more spiny. The four radial tubes of the mouth and the terminal caudal spine are very spiny (in the preceding species nearly smooth). The number of buccal holes (six to eight on each side of the mouth) is twice as great as in the former. Each circoral tube is pierced at the base by six or eight (in the former by four pores), and the base of the caudal spine exhibits a cross of four pores (in Tuscaridium cygneum only two pores).
Dimensions.—Length of the shell 3.6, breadth 1.8.
Habitat.—North Pacific, Station 264, depth 3000 fathoms.
Order IV. PHÆOCONCHIA, Haeckel, 1879.
Definition.—Phæodaria with a bivalved lattice-shell, composed of two free opposite valves (a dorsal and a ventral), between which the central capsule is enclosed.
Concharida, Haeckel, 1879, Sitzungsb. med.-nat. Gesellsch. Jena, Dec. 12, p. 6.
Definition.—Phæodaria with a bivalved lattice-shell, which is spherical or lenticular, and composed of two equal or unequal boat-shaped valves, a dorsal and a ventral. The valves bear neither an apical latticed cupola or galea, nor hollow radial tubes. The central capsule is placed in the aboral half of the shell-cavity, and so enclosed between both valves, that its three openings lie in the open frontal fissure between them (the astropyle on the oral pole of the main axis, the two parapylæ on both sides of its aboral pole, at right and left).
