dentated in the remaining 0.7 middle part; about fifty slender teeth of equal size on one lateral edge of each valve. In the half lateral perimeter of the shell about forty-five to fifty pores, in the half sagittal perimeter sixty-five to seventy, in the half equator thirty-two to forty pores. The pores are arranged in parallel curved rows, which are separated by high denticulate crests. Aboral hinge with a strong ligament.
Dimensions.—Length of the shell 0.6 to 0.7, height 0.55 to 0.65, breadth 0.35 to 0.45.
Habitat.—South Atlantic (east of Patagonia), Station 318, depth 2040 fathoms.
4. Conchopsis lenticula, n. sp. (Pl. 123, fig. 9).
Shell subcircular, lenticular, strongly compressed on both sides, with a sharp and broad hyaline keel in the sagittal perimeter. Borders of the two valves smooth in 0.3 of the oral, and 0.2 of the aboral part, strongly dentated in the remaining 0.5 middle part; about thirty strong, conical teeth on the lateral edge of each valve. In the half lateral perimeter of the shell fifty to fifty-five pores, in the half sagittal seventy to seventy-five, in the half frontal forty to forty-five pores. The large central capsule of this species fills up the posterior half of the shell-cavity, the dark green phæodium the anterior half; the latter contains numerous peculiar, longish, nucleated cells (fig. 9a), parasites or symbiontes (?). Aboral hinge of the shell with a strong ligament.
Dimensions.—Length of the shell 0.7, height 0.6, breadth 0.3.
Habitat.—Central Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.
5. Conchopsis pilidium, n. sp. (Pl. 125, fig. 9).
Shell ovate, lenticular, compressed on both sides, with a broad, wing-like sagittal keel. Proportion of its longitudinal diameter to the sagittal and lateral = 6 : 5 : 3. Sagittal perimeter elliptical. Borders of the two hat-like valves smooth in 0.15 of the oral, and 0.2 of the aboral part, strongly dentated in the remaining 0.65 middle part; about twenty-five to thirty teeth of nearly equal size on one side of each valve. In the half lateral perimeter of the shell (along one border of each valve) forty-five to fifty pores, in the half sagittal perimeter (on the keel of one valve) seventy to seventy-five pores, in the half equator thirty-six to forty pores. Each pore is surrounded by a hexagonal frame. The opening of each valve in this species is bordered and partly closed by a broad, horizontal diaphragm or velum, like the deck of a boat; it is broadest on the oral side.
Dimensions.—Length of the shell 0.78 to 0.8, height 0.66 to 0.7, breadth 0.3 to 0.4.
Habitat.—South Atlantic, between Buenos Ayres and Tristan da Cunha, Stations 324 to 334, at depths between 1715 and 2900 fathoms.
6. Conchopsis aspidium, n. sp. (Pl. 125, figs. 1, 2).
Shell scutiform, strongly compressed on both sides, in the centre only lenticular, in the periphery wing-like, keeled. Proportion of the longitudinal diameter to the sagittal and frontal = 6 : 5 : 2. Sagittal circumference in the oral half semicircular, in the aboral half pentagonal, two
