Page:Scientific results HMS Challenger vol 18 part 1.djvu/828

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Definition.— with a simple lentelliptical cortical shell, without radial spines. Medullary shell double, Larnacilla-shaped.

The genus Larnacalpis represents the most simple form of the sub-family Larnacalpida, and is very important as the common original form of all those in which a double Larnacilla-shaped medullary shell is surrounded by a simple, perfectly closed, latticed, lentelliptical cortical shell. Therefore the same typical, trizonal, lentelliptical shell, which in Larnacilla represents the external envelop (or cortical shell) of the central capsule, here in Larnacalpis becomes enclosed as an internal nucleus (or medullary shell) in the interior of the central capsule, and this latter becomes overgrown by a new lentelliptical cortical shell. The connection between the two shells of Larnacalpis is either effected by a number of radial beams (e.g., in Larnacalpis triaxonia by six beams situated in the three dimensive axes), or by two lateral, latticed, tube-like wings, which are repetitions of the smaller lateral wings connecting its external shell with the internal medullary shell (as in Larnacalpis lentellipsis). The latter species may be regarded as a Pylonium with a completely latticed shell.

1. Larnacalpis lentellipsis, n. sp. (Pl. 50, figs. 2, 2a, 2b).

Cortical shell with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; about sixteen on the half meridian, twelve on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Medullary shell one-third as large as the cortical, with four elliptical internal gates, connected with it by two opposite beams in the principal axis and by two latticed wings in the transverse axis; therefore between the two shells are four large kidney-shaped gates, halved by the polar beams (as in Octopyle).

Dimensions.—Length of the cortical shell (or principal axis) 0.14, breadth (or transverse axis) 0.11, height (or sagittal axis) 0.07; pores 0.01 to 0.02, bars 0.005; length of the medullary shell 0.05, breadth 0.04, height 0.03.

Habitat.—Pacific, central area, Station 273, depth 2600 fathoms.

2. Larnacalpis phacodiscus, n. sp.

Cortical shell with thorny surface and regular network; pores circular, twice as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell half as large as the cortical, with four kidney-shaped internal gates.

Dimensions.—Length of the cortical shell 0.13, breadth 0.11, height 0.09; pores 0.012, bars 0.006; length of the medullary shell 0.06, breadth 0.045, height 0.03.

Habitat.—North Pacific, Station 253, depth 3125 fathoms.