The genus Pylolena opens the series of the Hexapylida, or of those Pylodiscida in which the centre of the shell is formed by a tri-radiated medullary shell like Triopyle. In the equatorial plane of this triopyle-shaped disk are developed on its margin three distal arm chambers, as prolongations of the three arms of Triopyle, but much larger. In Pylolene the three angles or notches between the distal arms remain open, repeating the form of Triolene.
1. Pylolena inermis, n. sp.
Arms club-shaped, at the base half as broad, at the rounded distal end as broad as the triopyle-shaped medullary shell. Surface and margin smooth.
Dimensions.—Diameter of the cortical shell 0.15, of the medullary shell 0.05.
Habitat.—Equatorial Atlantic, Station 347, surface; Central Pacific, Station 272, surface.
2. Pylolena armata, n. sp. (Pl. [48], fig. 15).
Arms trapezoid, at the base half as broad, at the distal end twice as broad as the triopyle-shaped medullary shell. Surface and margin thorny. Twelve strong conical spines at the distal end of the three arms, two opposite on both faces of the arm-edges.
Dimensions.—Diameter of the cortical shell 0.2, of the medullary shell 0.06.
Habitat.—South Atlantic, Station 325, surface.