Family XXVIII. Zonarida, n. fam. (Pl. , figs. 9-12)

Definition.—Larcoidea with regular, completely latticed cortical shell, distinguished by two to four or more annular constrictions, which lie (all or partly) in the dimensive planes (sagittal, transverse, or lateral), and by which four to eight or more vaulted cupolas or dome-like chambers become separated. In the centre of this chambered cortical shell lies constantly a trizonal or Larnacilla-shaped medullary shell.

The family Zonarida comprises a small number of peculiar Larcoidea, resembling the Tholonida in the composition of the polythalamous cortical shell by a number of cupolas or dome-shaped protuberances. But the disposition and origin of these latter are quite different. Whilst in the Tholonida the axes of the domes are dimensive axes, and these are separated by annular constrictions lying in diagonal planes, in the Zonarida we find the contrary; the axes of the domes are here diagonal axes, and these are separated by annular constrictions lying in dimensive planes. However, this definition agrees absolutely only in the four-chambered Zonarium and in the eight-chambered Zonidium, whilst in the six chambered Zoniscus only four domes are disposed according to this law, two others, however, in the same manner as in the Tholonida. Therefore this genus is intermediate between both families.

The Cortical Shell of the Zonarida is in all cases completely latticed and of regular lentelliptical fundamental form, as in the nearly allied Larnacida and Tholonida. The three dimensive axes are constantly of different sizes, each with two equal poles; commonly (as in the human body) the principal or longitudinal axis is the longest, the sagittal (or dorso-ventral) axis the shortest; the transverse (or lateral) axis being intermediate between them. Of the three dimensive planes the lateral plane is the largest (determined by the principal and transverse axes); the smallest is the equatorial plane (crossed by the transverse and sagittal axes); the sagittal plane (determined by the sagittal and principal axes) being intermediate between them.

The annular constrictions of the cortical shell which produce the dome-shaped protuberances are different in number in the three known genera—two, three, or four. To each constriction often (but not always) corresponds an internal latticed septum, which connects the cortical with the medullary shell. The number of the cupolas is always double the number of the annular constrictions by which they are separated, therefore four, six, or eight.

In all known Zonarida the sagittal septum is quite constant, but derived from the original axial rod, which lies in the principal axis. By ramification of this axial beam and reticular connection with the sagittal girdle arises the sagittal septum, which we found first in Octopyle, halving the four gates of Tetrapyle. Whilst this sagittal septum (between right and left halves of the body) is common to all three known genera of this family, the number and shape of the other annular constrictions are different. In Zonarium (Pl. , fig. 9) we find only one transverse constriction (in the equatorial plane), in Zoniscus (figs. 10, 11) two parallel transverse constrictions (parallel to the equatorial plane, on both sides of it). Zonidium (fig. 12) is a combination of both foregoing genera; it has three parallel transverse constrictions (one in the equatorial plane, and one on each side of it).

The Latticed Domes (cupolas or chambers) of the cortical shell exhibit correspondingly a different number and disposition in the three known genera. In Zonarium are found only four crossed chambers, separated by the sagittal and transverse septa; the axes of the four crossed domes are diagonal axes, whilst in the similar Staurotholus they are dimensive axes (principal and transverse axes). In Zonidium we find eight domes, each cupola of Zonarium being halved by a diagonal septum. Zoniscus is intermediate between the two foregoing genera, and has six cupolas, three on each side of the sagittal septum.

The inner communication of the cupolas or chambers is more or less free, the lattice-work of the separating septa between them commonly remaining more or less imperfect, or represented only by some isolated beams or meshes. The outer network of the cupolas is commonly irregular (as in the majority of Larcoidea), but sometimes distinguished by a small number of regularly disposed larger apertures (similar to the "gates" of the Pylonida). From the surface radial spines often arise in characteristic number and symmetrical disposition, commonly as prolongations of the septal axes or of the constricted edges.

The Medullary Shell in all Zonarida is a true trizonal or Larnacilla-shaped lattice-shell (compare above, p. ); its perimeter (or the first lateral girdle) is sometimes more elliptical, at other times more hexagonal; the hexagon is amphithect; both its lateral sides are often concave and commonly longer than the four other sides.

The Central Capsule in all Zonarida is in a strict geometrical sense a true lentellipsis (compare above, p. ); its principal axis is commonly one and a third to one and a half times as great as the transverse axis, and twice to three times as great as the sagittal axis. The lentelliptical central capsule encloses the trizonal medullary shell, whilst it is externally enveloped by the chambered cortical shell.

Synopsis of the Genera of Zonarida.

Two annular constrictions and four cupolas, 301. Zonarium.

Three annular constrictions and six cupolas, 302. Zoniscus.

Four annular constrictions and eight cupolas, 303. Zonidium.

Genus 301. Zonarium, n. gen.

Definition.—Zonarida with four dome-shaped chambers of the cortical shell, separated by two annular constrictions (one sagittal and one transverse).

The genus Zonarium is the most simple form of the Zonarida, and differs from the nearly allied Larnacalpis by two ring-like constrictions, which are crossed at right angles, one in the sagittal (or median) plane, and one in the transverse (or equatorial) plane. By these two annular constrictions four egg-shaped or kidney-shaped chambers become imperfectly separated, which correspond to the quadrants of the lateral plane. The first cause of the marked constrictions may be the formation of the latticed sagittal septum, which is found first in Octopyle, as halving the four gates of Tetrapyle. Between this septum and the constricted narrow transverse girdle the cortical shell grows out in the form of four vaulted cupolas; every two opposite domes are congruent, two neighbouring are symmetrically equal.

1. Zonarium quadrigatum, n. sp.

Cortical shell quadrangular, one and a half times as long as broad, with four rounded corners. Surface thorny, with numerous short radial spines. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped.

Dimensions.—Length of the cortical shell 0.16, breadth 0.11; length of the medullary shell 0.06, breadth 0.04.

Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.

2. Zonarium quadrispinum, n. sp.

Cortical shell quadrangular, nearly rectangular, about twice as long as broad, with four corners, from which arise four strong, three-sided pyramidal, radial spines (crossed in two diagonals of the lateral plane). Surface thorny, only smooth in the transverse constriction. Sagittal constriction three times as long as the lentelliptical medullary shell. Four cupolas elliptical or nearly quadrangular.

Dimensions.—Length of the cortical shell 0.22, breadth 0.1; length of the medullary shell 0.07, breadth 0.05.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.

3. Zonarium octangulum, n. sp. (Pl. , fig. 9).

Cortical shell octangular, one and a fourth times as long as broad, with eight strong conical spines on the eight corners; these are separated by four deep constrictions on the poles of the principal and transverse axes, and by four truncated planes on the poles of the crossed diagonal axes between the former. Sagittal constriction twice as long as the hexagonal medullary shell. Four cupolas kidney-shaped or nearly pentagonal.

Dimensions.—Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

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

4. Zonarium tetratholium, n. sp.

Cortical shell quadrangular, with four rounded corners. Surface thorny, with sixteen stronger radial spines; eight of these lie in the lateral plane, in the same symmetrical disposition as in the foregoing species; eight others lie on both sides of the lateral plane, opposite in pairs in two crossed diagonal planes, in the same symmetrical disposition as in Tetrapyle octacantha. Sagittal constriction three times as long as the lentelliptical medullary shell. Four cupolas obliquely elliptical.

Dimensions.—Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.04, breadth 0.03.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

Genus 302. Zoniscus, n. gen.

Definition.—Zonarida with six dome-shaped chambers of the cortical shell, separated by three annular constrictions (one sagittal and two transverse, parallel to the equatorial plane).

The genus Zoniscus differs from Zonarium as well as from Zonidium by the development of the transverse girdle, which is not constricted, but on the contrary prominently vaulted in the equatorial plane. Therefore both wings of the transverse girdle form here two opposite lateral or "equatorial cupolas," as in Amphitholus. These are separated from four other domes (the "corner cupolas") by two transverse annular constrictions, which correspond to the free edges of the original transverse girdle. The corner domes of each pair are separated from each other by the sagittal septum.

1. Zoniscus rectangulus, n. sp.

Cortical shell nearly rectangular, with rounded corners, nearly one and a half times as long as broad. Surface thorny, without larger radial spines. Sagittal constriction scarcely half as long as the hexagonal medullary shell. Both equatorial cupolas (or wings of the transverse girdle) scarcely half as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.15, breadth 0.11; length of the medullary shell 0.07, breadth 0.045.

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

2. Zoniscus hexathalamus, n. sp.

Cortical shell nearly elliptical, one and a third times as long as broad. Surface nearly smooth, without radial spines. Sagittal constriction three times as long as the lentelliptical medullary shell. Both equatorial cupolas about as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.12, breadth 0.09; length of the medullary shell 0.035, breadth 0.025.

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

3. Zoniscus tetracanthus, n. sp. (Pl. , fig. 10).

Cortical shell nearly quadrangular, one and a half times as long as broad, with four prominent corners, from which arise in the lateral plane four strong, three-sided pyramidal radial spines (opposite in pairs in two crossed diagonal axes). Surface thorny, with exception of the concave lateral sides. Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas scarcely half as large as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.18, breadth 0.12; length of the medullary shell 0.07, breadth 0.04.

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

4. Zoniscus octacanthus, n. sp.

Cortical shell nearly four-sided, prismatic, one and a third times as long as broad, with spiny surface. Eight longer thin radial spines opposite in pairs in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction two and a half times as long as the hexagonal medullary shell. Both equatorial cupolas somewhat larger than the four corner cupolas.

Dimensions.—Length of the cortical shell 0.16, breadth 0.12; length of the medullary shell 0.055, breadth 0.04.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

5. Zoniscus hexatholius, n. sp. (Pl. , fig. 11).

Cortical shell nearly rectangular, with four rounded corners and deep sagittal constriction, one and a fourth times as long as broad with thorny surface. Twelve longer edged radial spines; eight opposite in pairs in two crossed diagonal planes (as in the foregoing species), four others in the lateral plane, opposite in pairs on both sides of the sagittal constriction, which is scarcely twice as long as the hexagonal, in the equatorial plane constricted medullary shell. Both equatorial cupolas nearly of the same size as the four corner cupolas.

Dimensions.—Length of the cortical shell 0.16, breadth 0.13; length of the medullary shell 0.07, breadth 0.04.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.

Genus 303. Zonidium, n. gen.

Definition.—Zonarida with eight dome-shaped chambers of the cortical shell, separated by four annular constrictions (one sagittal, one transverse, and two others parallel to the latter).

The genus Zonidium must be regarded as a Zonarium, in which the four cupolas (in the quadrants of the lateral plane) are halved by diagonal beams or latticed septa, lying opposite in pairs in two crossed diagonal planes. Therefore the number of the septa (four) and the domes (eight) is here doubled. Among the eight cupolas we distinguish four median (on both sides of the sagittal plane) and four lateral (on both sides of the equatorial plane); both groups are of different size and form. Probably Zonidium is derived from Zonarium by lattice-connection between the eight diagonal wing-spines, which in both species of this genus are present, the same as in Tetrapyle octacantha.

1. Zonidium octostylium, n. sp.

Cortical shell nearly quadrangular, with rounded corners and thorny surface. Eight long and thin radial spines on both sides of the lateral plane opposite in pairs and lying in two crossed diagonal planes (as in Tetrapyle octacantha). Sagittal constriction three times as long as the lentelliptical medullary shell. Four medial cupolas (on both sides of the sagittal plane) somewhat larger than the four lateral cupolas (on both sides of the equatorial plane).

Dimensions.—Length of the cortical shell 0.15, breadth 0.12; length of the medullary shell 0.05, breadth 0.03.

Habitat.—Indian Ocean, Madagascar, Rabbe, surface.

2. Zonidium octotholium, n. sp. (Pl. , fig. 12).

Cortical shell nearly octangular, with spiny surface; twenty long and stout radial spines between numerous smaller spines; eight wing-spines opposite in pairs in two crossed diagonal planes (as in the preceding species); twelve other strong spines in the lateral plane (four longer opposite in pairs on the poles of the principal and transverse axes, eight others smaller, alternating between these and the diagonal spines). Sagittal constriction twice as long as the hexagonal medullary shell. Four median cupolas somewhat smaller than the four lateral cupolas.

Dimensions.—Length of the cortical shell 0.18, breadth 0.15; length of the medullary shell 0.07, breadth 0.05.

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