The genus Staurotholonium differs from the nearly allied Staurotholus (its probable ancestral form) only in the duplication of the cortical shell. The outer shell commonly repeats the cross-form of the inner, with four corresponding cupolas; but sometimes the four cupolas of the outer shell alternate in size and form with those of the inner, or the outer shell forms a simple lenticular envelope around the inner. From the similar Tholoma, Staurotholonium differs in the possession of a medullary shell in the central chamber.
Definition.—Surface of the outer cortical shell smooth or rough, without radial spines.
1. Staurotholonium biquadratum, n. sp.
Outer cortical shell smooth, of the same regular crucial form as the inner, equidistant from it everywhere. Form and structure of both cortical shells nearly the same, but the outer about twice as large as the inner; both connected only by eight diagonal beams. All four cupolas of each cortical shell regular, of the same size. Pores regular, circular, twice as broad as the bars; six to eight in the basal semicircle of each cupola. Medullary shell square. (Similar to Staurotholus quadratus, but differs by the double cortical shell.)
Dimensions.—Diameter of the outer cortical shell 0.16, of the inner 0.08, of the medullary shell 0.04; pores of the inner cortical shell 0.006, bars 0.003.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
2. Staurotholonium bicruciatum, n. sp.
Outer cortical shell rough, twice as large as the inner, of the same form and structure, at an equal distance from it. In both shells the principal cupolas are larger than the lateral. Pores irregular, roundish, in the outer shell four times, in the inner twice as large as the bars; eight to ten in the basal semicircle of one cupola. (Similar to Staurotholus cruciatus, but differs mainly in the double cortical shell.) Medullary shell lentelliptical.
Dimensions.—Major (longitudinal) axis of the outer cortical shell 0.016, of the inner 0.08; minor (transverse) axis of the former 0.14, of the latter 0.07; medullary shell 0.03 to 0.04.
Habitat.—Pacific, central area, Station 267, depth 2700 fathoms.
3. Staurotholonium alternatum, n. sp.
Outer cortical shell smooth, very different from the inner; in the outer the two principal cupolas are larger than the two lateral; in the inner inversely smaller. Pores subregular, circular, in the outer shell four times, in the inner shell twice as broad as the bars; ten to twelve pores in the basal semicircle of one cupola.
Dimensions.—Major axis (length) of the outer cortical shell 0.15, minor (breadth) 0.13; pores 0.012, bars 0.003; major axis (length) of the inner cortical shell 0.11, minor axis (breadth) 0.09; pores 0.006, bars 0.003.
Habitat.—Indian Ocean, surface, Madagascar, Rabbe.
4. Staurotholonium lenticulare, n. sp.
Outer cortical shell smooth, lenticular, with circular circumference, with very delicate irregular network and small roundish pores. Its distance from the inner much greater in the four diagonal points than in the four polar points. Inner cortical shell regular, cross-like, with four cupolas of similar size and form. Pores subregular, circular, twice as broad as the bars; eight to ten in the basal semicircle of one cupola. Medullary shell lenticular.
Dimensions.—Diameter of the outer cortical shell 0.16, of the inner 0.12; pores of the inner 0.008, bars 0.004.
Habitat.—North Atlantic, Station 353, surface.
Definition.—Surface of the outer cortical shell with radial spines or thorns.
5. Staurotholonium octodoratium, n. sp.
Outer cortical shell of the same form and structure as the inner, but twice as large, both principal domes somewhat larger than both lateral. Pores subregular, circular, of the same breadth as the bars; five to six in the semicircle of one inner, eight to ten of one outer cupola. Eight thin and long bristle-like spines, opposite in pairs in two crossed diagonal planes.
Dimensions.—Major axis of the outer cortical shell 0.15, minor 0.12; major axis of the inner cortical shell 0.07, minor 0.06; pores and bars 0.005.
Habitat.—North Pacific, Station 231, surface.
6. Staurotholonium octodoronium, n. sp. (Pl. 10, fig. 11).
Outer cortical shell of the same form as the inner, both little distant; network of the outer irregular and delicate. Pores of the inner regular, circular, twice as broad as the bars; seven to nine in the basal semicircle of one cupola. Both lateral domes larger than the principal. Eight long and thin, cylindrical radial spines opposite in pairs in two crossed diagonal planes.
Dimensions.—Major axis of the outer cortical shell 0.2, minor 0.18; major axis of the inner cortical shell 0.16, minor 0.14; pores 0.008, bars 0.004.
Habitat.—South Pacific, Station 288, surface.
Definition.—Tholonida with triaxial growth; cupolas lying in pairs on the six sides of a cubical central chamber, opposite at the poles of three axes perpendicular one to another. (Shell commonly seven-chambered, with six domes surrounding the central chamber.)
Definition.—Tholonida with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).
The genus Tholocubus is the most simple form of the Cubotholida, or of the Tholonida with domes situated in three axes perpendicular one to another; six hemispherical cupolas lying on the six sides of a cuboidal central chamber; this latter contains no medullary shell. Tholocubus may be derived phylogenetically either from Tholostaurus by apposition of two opposite domes on the flat sides of the cross-shell, or from Cubotholus by loss of the medullary shell.
Definition.—Surface of the shell smooth or rough, without radial spines.
1. Tholocubus tessellatus, n. sp. (Pl. 10, fig. 12).
Surface of the shell smooth, without radial spines. Pores regular, circular, hexagonally framed, twice as broad as the bars; eight to twelve pores on the semicircle of one cupola. Principal cupolas smaller than the lateral, larger than the sagittal cupolas.
Dimensions.—Diameter of the shell 0.15; pores 0.01, bars 0.005.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
2. Tholocubus tesserarius, n. sp.
Surface of the shell rough, without radial spines. Pores irregular, roundish, once to three times as broad as the bars; twelve to sixteen pores in the semicircle of one cupola. All six cupolas nearly of the same size.
Dimensions.—Diameter of the shell 0.16; pores 0.004 to 0.008, bars 0.003.
Habitat.—North Atlantic, Station 353, depth 2965 fathoms.
Definition.—Surface of the shell with radial spines or thorns.
3. Tholocubus tesseralis, n. sp. (Pl. 10, fig. 16).
Surface of the shell with numerous (eight to sixteen) thin and long, bristle-shaped radial spines (the greater part broken off in the figured specimen); pores subregular, circular, three to four times as broad as the bars; ten to twelve in the semicircle of one cupola.
Dimensions.—Major axis of the shell 0.16, minor axis 0.14; pores 0.01, bars 0.0027.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
Definition.—Tholonida with double cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the simple cuboidal central chamber (without medullary shell).
The genus Tholonium (Pl. 10, fig. 17) differs from the preceding Tholocubus only in the duplication of the cortical shell. The outer (secondary) shell forms either a simple (spheroidal or ellipsoidal) thin veil around the inner (primary) shell, or both shells are of the same form, with six corresponding cupolas. Possibly Tholonium is the offspring of Cubotholonium, having originated by loss of the medullary shell.
Definition.—Surface of the shell smooth or rough, without radial spines or thorns.
1. Tholonium bicubicum, n. sp.
Outer shell with six hemispherical dome-shaped protuberances, corresponding in those of the inner shell. Both shells connected by numerous radial beams. Surface of the outer shell smooth; its network nearly of the same shape as that of the inner, with subregular, circular pores, twice as broad as the bars; ten to fifteen pores on the semicircle of one cupola.
Dimensions.—Diameter of the outer shell 0.14, of the inner 0.12; pores of the latter 0.006, bars 0.003.
Habitat.—South Atlantic, Station 325, depth 2650 fathoms.
2. Tholonium ellipticum, n. sp.
Outer shell ellipsoidal, without dome-shaped protuberances, with smooth surface, without radial spines; network delicate, with subregular, circular pores. Inner shell with regular, circular, hexagonally framed pores, twice as broad as the bars; ten to twelve pores on the semicircle of one cupola.
Dimensions.—Major axis of the outer shell 0.16, minor axis 0.14; major axis of the inner shell 0.14, minor axis 0.12; pores 0.008, bars 0.004.
Habitat.—Pacific central area, Station 267, depth 2700 fathoms.
3. Tholonium sphæricum, n. sp.
Outer shell spherical, without dome-shaped protuberances, with smooth surface, without radial spines; network very delicate, with very small subregular, circular pores. Inner shell with regular, circular pores of the same breadth as the bars; fourteen to sixteen on the basal semicircle of one cupola.
Dimensions.—Diameter of the spherical outer shell 0.15, inner shell 0.12; pores and bars of the inner shell 0.005.
Habitat.—Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.
Definition.—Surface of the outer shell covered with radial spines or thorns.
4. Tholonium hexonium, n. sp. (Pl. 10, fig. 17).
Outer shell ellipsoidal, without dome-shaped protuberances, covered with numerous (thirty to fifty) thin and long, bristle-shaped radial spines; network very delicate, irregular, with roundish pores. Inner shell with six marked hemispherical domes of somewhat different sizes; pores regular, circular, with prominent hexagonal frames, twice as broad as the bars; ten to twelve on the basal semicircle of one cupola.
Dimensions.—Major axis of the outer shell 0.15, minor axis 0.14; major axis of the inner shell 0.13, minor axis 0.12; pores 0.008, bars 0.004.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
5. Tholonium sphæronium, n. sp.
Outer shell very thin walled, spherical, without dome-shaped protuberances, with smooth surface, excepting eight large radial spines, rising from the eight corners of the inner cubical central chamber. Pores of the outer shell very small, subcircular. Inner shell very thick walled, with six marked hemispherical domes; pores subregular, circular, with prominent hexagonal frames, twice as broad as the bars; six to eight on the semicircle of one cupola.
Dimensions.—Diameter of the spherical outer shell 0.15, inner shell 0.11; pores of the inner 0.01, bars 0.005.
Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.
Definition.—Tholonida with simple cortical shell (without external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal Larnacilla-shaped central chamber (with medullary shell).
The genus Cubotholus differs from Tholocubus in the possession of a medullary shell in the central chamber, and may be derived from this genus by its production; but it may also be derived from Staurotholus by apposition of two opposite domes on the flat sides of the cross-shell. Sometimes all six domes are of the same size and form, but commonly different in pairs.
Definition.—Surface of the shell smooth or rough, without radial spines.
1. Cubotholus regularis, n. sp. (Pl. 10, fig. 14).
On the six sides of the cubical central chamber six hemispherical cupolas of the same size and form. Surface smooth. Pores regular, circular, twice as broad as the bars; eight in the basal semicircle of each cupola. Medullary shell apparently spherical (?), connected with the eight corners of the central chamber by eight radial beams, regularly disposed. (This species is remarkable for the perfect symmetry of the shell, the six sides of which appear to be quite similar. It differs from the similar Tholocubus regularis in the possession of a medullary shell.)
Dimensions.—Diameter of the cortical shell (equal in all three dimensive axes) 0.15; pores 0.01, bars 0.005; diameter of the medullary shell 0.04.
Habitat.—Pacific, central area, Station 273, depth 2350 fathoms.
2. Cubotholus quadraticus, n. sp.
Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the four other cupolas, which have the same size and lie cross-wise in the equatorial plane. (Therefore two of the three fundamental axes equal, the third larger.) Pores subregular, circular, three times as broad as the bars; ten to twelve in the semicircle of each cupola-basis.
Dimensions.—Major axis 0.16, minor axis 0.12; pores 0.012, bars 0.004.
Habitat.—Indian Ocean, Zanzibar, Pullen; depth 2200 fathoms.
3. Cubotholus rhombicus, n. sp.
Surface of the shell smooth. Both principal cupolas (on the poles of the longitudinal axis) larger than the two lateral (on the poles of the transverse axis), and these larger than the two sagittal cupolas (on the poles of the sagittal axis). Therefore all three fundamental axes unequal. Pores irregular, roundish, twice to four times as broad as the bars; eight to twelve in the basal semicircle of each cupola. Medullary shell lentelliptical.
Dimensions.—Major (principal) axis 0.16, middle (lateral) axis 0.14, minor (sagittal) axis 0.12; pores 0.006 to 0.012, bars 0.003.
Habitat.—South Atlantic, Station 335, depth 1425 fathoms.
Definition.—Surface of the shell with radial spines or thorns.
4. Cubotholus octoceras, n. sp.
All six cupolas in pairs of different sizes. Both principal domes larger than the lateral domes, and these larger than the sagittal domes. Pores subregular, circular, twice as broad as the bars; eight to ten in the semicircle of each cupola. From the surface arise (at the intersecting points of every three cupolas) eight strong conical radial spines, about as long as the shell-axis; they lie in two diagonal planes, and are the external free prolongations of eight inner beams (homologous with the eight wing-spines of Tetrapyle octacantha), which connect the lentelliptical medullary shell with the eight corners of the cuboidal central chamber.
Dimensions.—Major axis of the cortical shell 0.15, middle 0.13, minor 0.11; pores 0.008, bars 0.004; diameters of the medullary shell corresponding to 0.05, 0.04, 0.03.
Habitat.—Western Tropical Pacific, Station 224, depth 1850 fathoms.
Definition.—Tholonida with double (or sometimes triple) cortical shell (with external veil), composed of six hemispherical cupolas, opposite in pairs on the poles of three axes perpendicular one to another, covering six sides of the cuboidal Larnacilla-shaped central chamber (with medullary shell).
The genus Cubotholonium differs from the nearly allied Cubotholus (its probable ancestral form) only in duplication of the cortical shell. I have observed only two species of this rare form, both rather different. In the first species the outer cortical shell forms a simple spherical thin veil around the inner, the six cupolas of which are nearly of the same form and size. In the second species each of the domes of the inner cortical shell is protected by an outer larger cupola, and besides this the whole shell is enveloped by a thin ellipsoidal veil (Pl. 10, fig. 15). Therefore this species may be the representative of a peculiar genus, the most highly developed of all Tholonida—Tholothauma.
1. Cubotholonium sphæroides, n. sp.
Outer cortical shell (or veil) spherical, with smooth surface; network very delicate, with very thin bars and very small irregular, roundish pores. Inner cortical shell simple, composed of six hemispherical cupolas, surrounding the six sides of the cubical central chamber, which encloses a spherical medullary shell (one-third as large as itself). Network of the inner cortical shell regular, with circular pores of the same breadth as the bars, twelve to fourteen in the basal semicircle of one cupola.
Dimensions.—Diameter of the spherical outer shell 0.2, of the inner cortical shell 0.15; pores and bars of the latter 0.006.
Habitat.—Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.
2. Cubotholonium ellipsoides, n. sp. (Pl. 10, fig. 15).
Tholothauma ellipsoides, Haeckel, 1883, MS.
Outer cortical shell (or veil) ellipsoidal, with very thin irregular network and thorny surface. Inner cortical shell double, with six double, flatly vaulted cupolas, surrounding the six sides of the Larnacilla-shaped central chamber; the double domes of each shell are in opposite pairs somewhat larger than the alternating pairs. Pores subregular, circular, about the same breadth as the bars; eight to twelve in the basal semicircle of one cupola. Central chamber with ellipsoidal medullary shell. Radial spines short, very numerous.
Dimensions.—Major axis of the outer cortical shell 0.28, minor 0.24; major axis of the inner cortical shell 0.16, minor axis 0.14; pores and bars 0.006; medullary shell 0.03.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
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. 50, 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. 600); 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. 599); 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.
| Two annular constrictions and four cupolas, | 301. Zonarium. |
| Three annular constrictions and six cupolas, | 302. Zoniscus. |
| Four annular constrictions and eight cupolas, | 303. Zonidium. |
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. 50, 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.
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. 50, 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. 50, 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.
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. 50, 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.
Lithelida, Haeckel, 1862, Monogr. d. Radiol., p. 515.
Definition.—Larcoidea with symmetrical spiral shell, divided by the spiral plane into two symmetrical halves; all windings of the spiral lie in this plane. Primordial chamber either simple or Larnacilla-shaped.
The family Lithelida comprises all those Larcoidea in which the growth of the latticed shell is spirally winding in one plane, Nautilus-like. They agree in the spiral growth with the following family. But in the Streblonida the spiral is screw-shaped, ascending (like Helix). Therefore in these latter the geometrical fundamental form of the shell is asymmetrical or "dysdipleural," whereas in the Lithelida bilateral-symmetrical or "eudipleural." The lentelliptical or nearly spherical shell may be divided by a median section into two symmetrical halves; the right half is the mirror image of the left half.
When in 1862 I founded the family Lithelida in my Monograph (p. 515), I knew only one genus, Lithelius, with two species. The rich material of the Challenger collection contains a great number of similar spirally constructed Larcoidea, so that at the present time we may distinguish at least six genera. These belong to two different subfamilies, which may possibly be afterwards better separated as families. The first subfamily, Spiremida, possess a simple, spherical or subspherical, medullary shell; the second subfamily, Larcospirida, possess a trizonal or Larnacilla-shaped medullary shell. No doubt these latter must be derived from Pylonida, as we observe all stages of development starting from a simple Trizonium; but perhaps also the Spiremida have the same origin, their simple, spherical or subspherical, medullary shell being derived from a trizonal or Larnacilla-shaped medullary shell by reduction.
The general appearance in both subfamilies of the Lithelida is quite the same, and it requires a careful study of the medullary shell to distinguish certainly the Spiremida from the Larcospirida. This distinction is often not easy, particularly in the larger forms; the shell is often very opaque and difficult to understand. Only in one position, if the spiral axis be parallel to the axis of the eye of the observer, and the spiral plane be therefore fully seen in the optical plane of the microscope, the spiral line (or the axial section of the latticed spiral lamella) is distinctly observed; in all other positions the figure of the spiral is more or less indistinct, and the whole microscopical image often quite intricate and confused. The sufficient study of this family requires therefore the contemplation of the shell from different sides, and is the more difficult, as the variability of the Lithelida—as of the Pylonida—is extraordinarily great.
The description which I gave of Lithelius (1862) in my Monograph is in some points erroneous, and was afterwards (1879) corrected by R. Hertwig, who explained particularly the near relation of it to Tetrapyle. Indeed the intermediate forms between the Lithelida and the Pylonida are so numerous and so evident in all stages of development, that the derivation of the former (at least of the Larcospirida) from the latter is quite clear. The analogy between the structure of the Lithelida and the calcareous (foraminiferous) Alveolinida is not so complete as I supposed it to be in my Monograph (1862); particularly the formation of the small chambers between the turnings of the spiral lamella is much more complete in the Alveolinida than in the Lithelida.
The cortical shell of all Lithelida has the same geometrical fundamental form as Nautilus or as the nautiloid Polythalamia (Polystomella, Nummulites, &c.); therefore the shell is dipleural, being divided by the median plane into two symmetrical lateral halves. Since the spiral line lies in the median plane, we will call it the spiral plane; it separates the right half from the left. The axis of the body, around which the spiral turns (without touching it), is the spiral axis. The latticed part of the cortical shell, which turns around them, is the spiral lamella. Only in one genus of our family, viz., Tholospira, are the spiral axis, the lateral axis, the spiral plane, and the sagittal plane quite as in Nautilus. In all other genera this disposition is different or is uncertain. This depends on the different part of the cortical shell, from which the spiral growth begins. In this respect we can distinguish four different modes.
In the Larcospirida (or the Lithelida with Larnacilla-shaped medullary shell) the spiral growth exhibits four quite different forms. It begins here with Larcospira, in which already the first cortical girdle of the Diplozonaria determines the spiral growth; one wing of this girdle, the transverse girdle of Amphipyle, grows more swiftly than the other, overgrows it, and thus turns around the principal axis. In Pylospira the first or transverse girdle is already perfectly formed (as in Amphipyle), and the spiral growth is introduced by the second or lateral girdle of Tetrapyle; one wing of it (the right or the left) grows more swiftly than the other, overgrows it, and thus turns around the sagittal axis. In Tholospira also the second girdle is complete, and the spiral growth begins from the third or sagittal girdle. One of its wings grows more swiftly than the other, overgrows it, and thus turns around the transverse axis. Consequently we see that each of the three dimensive planes of the lentelliptical Larcoid-body may be the spiral plane: in Larcospira the transverse plane, in Pylospira the lateral plane, in Tholospira the sagittal plane. Correspondingly the spiral axis in the first genus is the principal, in the second the sagittal, in the third the transverse axis of the central Larnacilla-shell. Therefore in these three genera the spiral plane is the plane of the latticed girdle, which determines the spiral growth, one of both its wings overgrowing the other.
In each of the three above mentioned genera the spiral may be simple or double; it remains simple if only one of both wings of the turning girdle overgrow the other, and this latter remain a simple half girdle (or tube-like wing). Whereas the spiral becomes double if the second wing of the girdle afterwards follow the example of the first wing and now turn around it in the same direction. As this happens in all three genera, we can subdivide them into six subgenera.
A quite peculiar form of spiral growth is produced in Spironium, in which the direction of growth in both lateral wings of the transverse girdle is inverse from the beginning. The left wing grows against the posterior, the right wing against the anterior pole of the principal axis, turning around it in crossed, eight-like spirals. The whole shell afterwards assumes a lentelliptical form.
Commonly between the embracing spiral turnings or convolutions a great number of radial beams is developed, irregularly disposed and often branching; they support the thin spiral lamellæ and give to the whole shell more solidity. Often these beams form imperfect radial septa, by which the spiral cavity of the turnings is divided into a variable number of chambers. But these chambers never become so regular and perfect as in the analogous nautiloid Polythalamia.
In many Lithelida the growth of the shell reaches a certain limit, concluding with the formation of a superficial latticed lamella of lentelliptical or nearly spherical form. In many other forms of the family this seems not to be the case; but these may possibly be younger forms, afterwards reaching the same limit.
The network of the shell in the Lithelida is commonly quite irregular, and so variable that its special conformation has usually no value in the determination of the species. The surface of the shell is often covered with radial spines, which are sometimes arborescent.
The central capsule seems always to preserve the same lentelliptical form (or triaxial ellipsoid) as in all other Larcoidea. With the increase of growth it encloses successively a larger part of the spiral cortical shell, but on the outside is constantly protected by the last turnings of the spiral, or by the lattice-lamella of the surface.
|
II. Subfamily Spiremida. Central medullary shell simple, spherical or lentelliptical. |
brace | Surface of the cortical shell smooth or thorny, withou radial spines, | 304. Spirema. |
| Surface of the cortical shell covered with numerous simple or branched radial spines, | 305. Lithelius. | ||
|
II. Subfamily Larcospirida. Central medullary shell double, trizonal or Larnacilla-shaped. |
brace | The transverse girdle turns around the principal axis, | 306. Larcospira. |
| The lateral girdle turns around the sagittal axis, | 307. Pylospira. | ||
| The sagittal girdle turns around the transverse axis, | 308. Tholospira. | ||
| Both wings of the transverse girdle turn around the principal axis in an opposite diagonal direction, | 309. Spironium. |
| I. Subfamily Spiremida. Central medullary shell simple, spherical or lentelliptical. | ||||
| Surface of the cortical shell smooth or thorny, withou radial spines, | ||||
| 304. Spirema. | ||||
| Surface of the cortical shell covered with numerous simple or branched radial spines, | ||||
| 305. Lithelius. | ||||
| II. Subfamily Larcospirida. Central medullary shell double, trizonal or Larnacilla-shaped. | ||||
| The transverse girdle turns around the principal axis, | ||||
| 306. Larcospira. | ||||
| The lateral girdle turns around the sagittal axis, | ||||
| 307. Pylospira. | ||||
| The sagittal girdle turns around the transverse axis, | ||||
| 308. Tholospira. | ||||
| Both wings of the transverse girdle turn around the principal axis in an opposite diagonal direction, | ||||
| 309. Spironium. | ||||
Definition.—Lithelida with simple, spherical or subspherical, medullary shell.
Definition.—Lithelida with simple, spherical or subspherical, medullary shell, and lentelliptical or subspherical, spirally constructed cortical shell; surface smooth or thorny, without radial spines.