Distance between the paired arms about half as large as their distance from the odd arm. All three arms nearly of the same size and form, about twice as long as broad, one and a half times at the blunt convex end as broad as at the base. Patagium incomplete, with concave chamber-rows and irregular network, only enveloping the basal half of the arms.
Dimensions.—Radius of all three arms 0.15, basal breadth of each arm 0.04, terminal breadth 0.06.
Habitat.—North Pacific, Californian Sea, depth 2600 fathoms, Ehrenberg.
2. Euchitonia mülleri, Haeckel.
Euchitonia mülleri, Haeckel, 1862, Monogr. d. Radiol., p. 508, Taf. xxx. figs. 5-10.
Euchitonia mülleri, Stöhr, 1880, Palæontogr., vol. xxvi. p. 110, Taf. v. fig. 5.
Distance between the paired arms about two-thirds as large as their distance from the odd arm, which is somewhat larger. Length of the arms equals two and a half times the breadth of the blunt convex end or five times the breadth of the base. Patagium with concave chamber-rows, nearly complete, enveloping the arms with exception of the terminal face. (This common species is very variable; compare my Monograph.)
Dimensions.—Radius of all three arms 0.16 to 0.22, basal breadth 0.03 to 0.05, terminal breadth 0.06 to 0.08.
Habitat.—Cosmopolitan; one of the most common Discoidea in all seas, on the surface as well as at different depths; also fossil in the Tertiary rocks of Barbados and Sicily.
3. Euchitonia triangulum, Haeckel.