quadrangular pyramid, without leaf-cross. All the twenty spines of this species exhibit nearly the same form, which is seen in the frontal or anterior (hydrotomical) spine of Amphilonche anomala (Monogr. d. Radiol., Taf. xviii. fig. 23, a).
Dimensions.—Length of the spines 0.15, breadth in the middle part 0.012, on both ends 0.025.
Habitat.—South Pacific, Station 288, surface.
8. Acanthonia quadrangula, n. sp.
Spines quadrangular prismatic, with smooth prominent straight edges, but of very different breadth in both halves; the inner or proximal half (inside the central capsule) twice to four times as broad as the outer or distal half (outside the central capsule); both ends suddenly separated by a constriction, in which is inserted the membrane of the capsule. The latter is pellucid, with a number of yellow bodies. Apex of the spines simple, base pyramidal, without leaf-cross.
Dimensions.—Length of the spines 0.2 to 0.4, breadth of the basal half 0.01, of the distal half 0.002 to 0.004.
Habitat.—Atlantic, Canary Islands, Azores, Station 354, surface.
Subgenus 2. Acanthonidium, Haeckel.
Definition.—Spines at the central base with a broad leaf-cross, composed of four prominent triangular lamellæ; the meeting edges of these crossed lamellæ between every three or four neighbouring spines so rest one upon another that twenty-two hollow pyramidal compartments are formed (compare p. 721).
9. Acanthonia echinoides, Haeckel.
Spines quadrangular prismatic without prominent edges, with four plane lateral faces, of equal breadth throughout their whole length. Central base three to four times as broad, with large leaf-cross. Apex truncated or bifid (sometimes with four short teeth).
Dimensions.—Length of the spines 0.3 to 0.5, breadth 0.004 to 0.008; leaf-cross 0.02 to 0.03.
Habitat.—North Atlantic, west coast of Norway (Claparède et Lachmann); Færöe Channel (Gulf Stream), John Murray, surface.
10. Acanthonia claparedei, Haeckel.
Spines quadrangular prismatic, with four prominent lamellar edges, of equal breadth throughout their whole length. Apex bifid. Central base twice as broad, with large leaf-cross. Central capsule opaque, reddish-brown.
Dimensions.—Length of the spines 0.6, breadth 0.016; leaf-cross 0.032.
Habitat.—Mediterranean (Messina); Atlantic, Station 347, surface.
