Shell subcircular, lenticular, strongly compressed on both sides, nearly as high as long, its sagittal perimeter nearly circular; frontal and cinctural perimeter spindle-shaped. Borders of the two boat-shaped valves smooth in 0.4 of the oral part, and in 0.1 of the aboral part of their length, strongly dentated in the remaining 0.5 middle part; about twenty-five slender, straight teeth on each side of one valve, size of the teeth increasing from the aboral towards the oral pole. In the half lateral perimeter of the shell (along the right and the left borders of each valve) sixty to sixty-five pores, in the half sagittal perimeter (along the keel of each valve) eighty to eighty-five pores, in the half equator sixty to sixty-five pores.
Dimensions.—Length of the shell 0.53, height 0.55, breadth about 0.2.
Habitat.—South Atlantic, west of Tristan da Cunha, Station 333, depth 2025 fathoms.
2. Conchopsis compressa, n. sp. (Pl. [125], figs. 7, 8).
Shell lenticular, strongly compressed on both sides; proportion of its longitudinal diameter to the sagittal and lateral = 10 : 9 : 3, its sagittal perimeter elliptical (fig. 7), cinctural and frontal perimeter spindle-shaped (fig. 8). Borders of the two boat-shaped valves smooth in 0.3 of the oral, and 0.3 in the aboral part, dentated in the remaining 0.4 middle part; about forty to forty-four very slender teeth of equal size on one lateral edge of each valve. In the half frontal perimeter of the shell (along the border of the valve) sixty-four to sixty-eight pores, in the half sagittal perimeter (along one valve-keel) seventy to eighty pores, in the half equator forty-four to forty-eight pores. Ventral and dorsal pores linear, three to four times as long as the circular, lateral pores.
Dimensions.—Length of the shell 0.6 to 0.8, height 0.55 to 0.72, breadth 0.2 to 0.3.
Habitat.—North Pacific, between 30° and 40° north latitude (between Japan and San Francisco), in depths from 2000 to 3000 fathoms frequent, Stations 241 to 252.
3. Conchopsis carinata, n. sp. (Pl. [123], fig. 8).
Shell subcircular, lenticular, in the central half slightly compressed, nearly spherical, in the peripheral half strongly compressed, with a broad, hyaline, smooth keel on the sagittal plane. Borders of the two valves smooth in the 0.2 of the oral, and 0.1 of the aboral part, strongly 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.