Shell-mantle one and a half times as long as broad; its frontal perimeter pentagonal, with a deep median incision at the base; the two oral sides of the pentagon twice as long as the two lateral sides, and one and a half times as long as the base. Sagittal perimeter ovate; equatorial perimeter subcircular. Nasal odd style of each valve with fourteen to sixteen pairs of branches, one and a half times as long as the paired frontal styles (each with eight to nine pairs), and twice as long as the paired tergal styles (each with four to six pairs of branches). Terminal coronets (on the free distal ends of the styles) richly branched, each with thirty to forty thorny fingers, which bear a conical point with recurved teeth, like an arrow.
Dimensions.—Length of the shell 3.2, breadth 2.1.
Habitat.—Tropical Atlantic, Station 347, depth 2250 fathoms.
2. Cœlodecas decastyla, n. sp.
Shell-mantle one and a third times as long as broad; its frontal perimeter pentagonal, with a slight incision on the base; the two oral sides of the pentagon as long as the base, and one and a half times as long as the two lateral sides. Nasal odd style of each valve with ten to twelve pairs of branches, about twice as long as the four paired frontal and tergal styles, each of which bears five or six pairs. Terminal coronets three times forked, each with eight straight, spinulate, slightly divergent fingers, shaped like a human finger.
Dimensions.—Length of the shell 3.6, breadth 2.7.
Habitat.—Central Pacific, Station 272, depth 2600 fathoms.
3. Cœlodecas pentagona, n. sp.
Shell-mantle about as long as broad; its frontal perimeter nearly regular pentagonal, with five equal sides. Nasal odd style of each valve with six to eight pairs of branches scarcely longer than the four paired frontal and tergal styles, each of which is provided with four to six pairs. Terminal coronets irregularly branched, each with twelve to sixteen slender curved fingers, which bear at the distal end a spinulate knob.
Dimensions.—Length of the shell 2.6, breadth 2.4.