Page:Scientific results HMS Challenger vol 18 part 1.djvu/864

656 6. Pylonium stenozonium, n. sp.

Cortical shell thorny, with eight short conical radial spines, lying in two crossed diagonal planes (as in the foregoing species). All three girdles nearly of the same size, subcircular, very narrow, only with one to two rows of pores. Four gates kidney-shaped.

Dimensions.—Principal axis 0.15, transverse axis 0.14; diameter of the quadrangular medullary shell 0.04.

Habitat.—Equatorial Atlantic, Station 347, surface.

Definition.— with three concentric systems of fenestrated girdles, lying in three concentric lentelliptical faces (every system with one to three girdles lying in one lentelliptical face).

Definition.— with trizonal lentelliptical medullary shell, surrounded by a double latticed cortical shell; inner cortical shell Pylonium-shaped, with three perfect crossed girdles; outer cortical shell only represented by a single (transverse) girdle.

The genus Amphipylonium opens the series of Triplozonaria, or of those Pylonida in which the shell is composed of three concentric systems of latticed girdles. The first (and innermost) system represents the complete trizonal medullary shell, which is probably a lentelliptical Larnacilla-shell. The first and intermediate system is formed of a complete trizonal cortical shell of the same form, but much larger (like Pylonium). The third (and outermost) system is represented by one to three latticed girdles, corresponding to the former and forming an outer or second cortical shell. In Amphipylonium (as the most simple form of the Triplozonaria) there is only developed the first (transverse) girdle of the third system. It repeats therefore the form of Amphipyle, the cortical shell of which is here double (Prodromus, 1881, p. 463).

1. Amphipylonium semilunare, n. sp.

Inner cortical shell lentelliptical, one and a half times as long as broad, with smooth surface and four semilunar gates. Transverse girdle of the outer cortical shell with two smooth semilunar wings, with convex, smooth lateral crests; each wing as broad as the transverse girdle of the inner cortical shell and twice as long as its lateral girdle.

Dimensions.—Length of the lentelliptical medullary shell 0.04, breadth 0.03; length of the inner cortical shell 0.15, breadth 0.1; length of each lateral wing of the outer cortical shell 0.3, breadth 0.1.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.