Subfamily 1. Larnacillida, Haeckel

Definition.—Larnacida with a simple, spherical or lentelliptical, medullary shell, connected by the lateral wings of a latticed transverse girdle with the simple lentelliptical trizonal cortical shell; the central capsule encloses the former and is enveloped by the latter.

Genus 272. Larnacilla, n. gen.

Definition.—Larnacida with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface without radial spines.

The genus Larnacilla represents the most simple form of Larnacida, and at the same time the most important common ancestral form, from which the greater number of Larcoidea may be derived, viz., all those genera which possess the characteristic "Larnacilla-shaped medullary shell." This typical form of medullary shell may be derived from the genus Trizonium among the Pylonida by the closing of the four open gates of this genus. The free opening of these four gates becomes overgrown and closed by lattice-work, developed from the free edges of the three crossed girdles, and thus finally all three girdles are united in the form of a simple lentelliptical shell (Pl. , figs. 1, 1a, 1b). Seen from the sagittal poles (or from the poles of the shortest axis, fig. 1), the shell exhibits on both sides of the small spherical medullary shell the two lateral wings of the transverse girdle from the face; seen from the lateral poles (or from the poles of the transverse axis, fig. 1a), one of these wings appears in the optical section as an oblong ring, which seemingly encloses the concentric medullary shell, and on both sides is grown together with the sagittal girdle; seen from the principal poles (or from the poles of the longitudinal axis, fig. 1b), both wings exhibit their elliptical opening (at the right and left from the central medullary shell). The two concentric shells are only connected by the two lateral tube-like wings of the transverse girdle; the lateral and the sagittal girdles have no connection with the medullary shell. The latter is sometimes spherical, at other times lentelliptical.

1. Larnacilla typus, n. sp. (Pl. , fig. 1, 1a, 1b).

Cortical shell with smooth surface and with subregular network; pores twice as broad as the bars; about twelve pores on the half meridian, ten on the half equator. Proportion of the three dimensive axes = 2 : 3 : 4. Internal four gates (between transverse and lateral girdles) roundish-triangular, little broader than high. Medullary shell spherical, scarcely one-third as broad as the lentelliptical cortical shell.

Dimensions.—Length of the cortical shell (or principal axis) 0.13, breadth of it (or transverse axis) 0.1, height of it (or sagittal axis) 0.07; pores 0.006, bars 0.003; medullary shell (diameter) 0.03.

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

2. Larnacilla prometor, n. sp.

Cortical shell with rough surface and regular network; pores three times as broad as the bars; about ten on the half meridian, eight on the half equator. Proportion of the three axes = 1 : 2 : 3. Internal four gates (between transverse and lateral girdles) kidney-shaped, twice as broad as high. Medullary shell lentelliptical, of the same form as the external cortical shell, but only one third as large.

Dimensions.—Length of the cortical shell 0.15, breadth 0.1, height 0.05, pores 0.015, bars 0.005; medullary shell 0.02 to 0.05.

Habitat.—Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

3. Larnacilla subglobosa, n. sp.

Cortical shell nearly spherical, with thorny surface and irregular network; pores roundish, twice to four times as broad as the bars; twelve to sixteen in the half circumference. Proportion of the three axes very little different = 1.3 : 1.4 : 1.5. Internal four gates elliptical, one and a half times as broad as high. Medullary shell spherical, one-fourth as broad as the cortical shell.

Dimensions.—Length of the cortical shell 0.15, breadth 0.14, height 0.13; pores 0.006 to 0.012, bars 0.003; medullary shell 0.035.

Habitat.—Pacific, central area. Station 266, depth 2750 fathoms.

4. Larnacilla medullaris, n. sp.

Cortical shell lentelliptical, with smooth surface and irregular network; pores roundish, very small, scarcely as broad as the bars; about eight to nine on the half meridian, six to seven on the half equator. Proportion of the three axes = 3 : 4 : 6. Internal four gates elliptical. Medullary shell spherical, scarcely one-third as broad as the cortical shell. (This small species may be only the medullary shell of some other Larcoid, the cortical shell of which is not yet formed.)

Dimensions.—Length of the cortical shell 0.06, breadth 0.04, height 0.03; pores and bars about 0.004; medullary shell 0.013.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Genus 273. Larnacidium, n. gen.

Definition.—Larnacida with a simple lentelliptical cortical shell, connected by the lateral wings of a latticed transverse girdle with the simple, spherical or lentelliptical, medullary shell. Surface armed with radial spines.

The genus Larnacidium has the same shell-formation as the foregoing Larnacilla, and differs from it only in the possession of radial spines on the surface, which in all known species exhibit a symmetrical disposition. From the nearly allied genus Larcidium it differs in the characteristic mode of connection between the two shells, owing to the different kind of growth. In Larcidium this connection is effected only by radial beams, whereas in Larnacidium (as in all Larnacida) by two lateral latticed tubes, the wings of the primary transverse girdle.

1. Larnacidium staurobelonium, n. sp.

Cortical shell smooth, with four strong conical, radial spines in the lateral plane, opposite in pairs, two on the poles of the principal and two on the poles of the transverse axis. Pores subregular, circular, twice as broad as the bars; about twelve on the half meridian. Proportion of the three axes = 2 : 3 : 4. Medullary shell spherical, one-third as broad as the cortical shell.

Dimensions.—Length of the cortical shell 0.12, breadth 0.09, height 0.06; pores 0.008, bars 0.04; medullary shell 0.03.

Habitat.—North Pacific Station 244, depth 2900 fathoms.

2. Larnacidium hexabelonium, n. sp.

Cortical shell thorny, with six strong, three-sided pyramidal, radial spines, lying opposite in pairs on the poles of the three dimensive axes. Pores subregular, circular, three times as broad as the bars; about fourteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell spherical, one-third as broad as the cortical shell.

Dimensions.—Length of the cortical shell 0.14, breadth 0.11, height 0.08; pores 0.01, bars 0.003; medullary shell 0.04.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.

3. Larnacidium polybelonium, n. sp.

Cortical shell very spiny, with numerous (twenty to thirty or more) larger thin radial spines, about as long as the shell. Pores irregular, twice to five times as broad as the bars; about sixteen on the half meridian. Proportion of the three axes = 2 : 2.5 : 3. Medullary shell lentelliptical, half as large as the cortical shell.

Dimensions.—Length of the cortical shell 0.11, breadth 0.09, height 0.07; pores 0.004 to 0.01, bars 0.002; length of the medullary shell 0.06, breadth 0.05, height 0.04.

Habitat.—Western Tropical Pacific, Station 225. depth 4475 fathoms.