Family XLIII. Hexalaspida, n. fam. (Pl. )

Definition.—Acantharia with a simple discoidal or lenticular lattice-shell, composed of the branched apophyses of twenty radial spines meeting in the centre and disposed according to the Müllerian law of Icosacantha. Six larger spines in the hydrotomical plane, prominent on the margin of the circular or elliptical biconvex lens. Fourteen other spines much smaller or rudimentary. Central capsule biconvex lenticular, enclosed in the fenestrated shell.

The family Hexalaspida represents a new small, but very interesting group of Acanthophracta, which differs from all others in the lentelliptical or triaxial form of the lenticular lattice-shell, the margin of which bears six larger spines placed in the hydrotomical plane (compare above, p. ). They may therefore be characterised shortly as "Acanthophracta lentelliptica," with three different dimensive axes and six larger marginal spines. A closer comparison with the other Acantharia leaves no doubt that the Hexalaspida must be derived from the Belonaspida by stronger development of six radial spines placed in the hydrotomical plane, namely, two equatorial and four associated polar spines; whilst the six spines of the geotomical plane (perpendicular to the former) are much smaller; the eight tropical spines are intermediate in size between the former and the latter.

The geometrical fundamental form of the Hexalaspida (of the central capsule as well as of the enclosing shell) is therefore lentelliptical, with three different dimensive axes, and they exhibit among the Acantharia a relation to the spherical Dorataspida and the ellipsoidal Belonaspida similar to that which the lentelliptical Larcoidea exhibit to the spherical Sphæroidea and the ellipsoidal Prunoidea among the Sphærellaria (compare above, p. ). The largest of the three dimensive axes (which are perpendicular to one another) is here the hydrotomical axis, the shortest, on the contrary, the geotomical axis; the intermediate in size being the spineless axis. The development of the whole body is strongest in the hydrotomical meridian plane, in which the six principal spines are placed; it is weakest in the geotomical plane, in which the six smallest spines are placed; the eight tropical spines are intermediate in size between the others. This peculiar development is illustrated by the figures of Pl. , where the four equatorial spines are everywhere marked by c, the eight tropical spines by b and d, the eight polar spines by a and e.

Rarely the six hydrotomical or principal spines are of equal size, and thus the margin of the shell may be quite circular or regularly hexagonal (Pl. , figs. 1-3); the two equatorial spines of the hydrotomical plane are usually larger than its four polar spines, and thus the margin of the shell becomes more or less elliptical (Pl. , figs. 4-7). Usually (almost constantly) these six larger spines are more or less compressed, triangular, often very broad and flat; their two edges lie in the hydrotomical plane. Their two flat surfaces are often furrowed, with longitudinal ribs or crests converging towards the simple apex of the spines.

The fourteen smaller spines are regularly disposed according to the Müllerian law of Icosacantha on both convex sides of the lenticular shell; they are not only smaller than the six principal spines, but often also of different form, much thinner and shorter, sometimes needle-shaped. In the genera Hexonaspis and Hexacolpus (Pl. , figs. 1, 2) only their inner part (inside of the shell) is developed, whilst their outer part is quite rudimentary and not prominent on the surface. Therefore these genera appear to possess only six marginal spines externally.

The Lenticular Shell itself offers in the Hexalaspida great difficulties in the way of accurate study, as its wall is constantly very thick and dark, often quite opaque and non-transparent. However, prolonged accurate researches have convinced me that its structure is essentially the same as in the Belonaspida and especially in the genera Dictyaspis and Coleaspis. As in these latter the twenty plates of the shell bear high crests or combs on the outer surface, and by these funnel-shaped dimples are separated. The network of these crests is more or less regular (Pl. , figs. 1-7). Around the base of each radial spine the shell is usually elevated in the form of a conical or cylindrical sheath; the crests are prolonged into the sheaths as longitudinal ribs, parallel to the spine or convergent towards its apex. Whilst in Hexalaspis and Hexonaspis these basal sheaths are not at all or but little prominent (Pl. , fig. 2; Pl. , fig. 16), in Hexaconus and Hexacolpus they envelop the basal half (or even more) of the spines, and very often the circular or elliptical free distal edge of the sheath is elegantly denticulated or serrated (Pl. , figs. 1, 3-7; pl. 140, figs. 9-16).

The Pores of the shell exhibit in the Hexalaspida the same shape as in the majority of the Belonaspida. Each spine bears only two broad opposite apophyses, the fork-branches of which unite to form a polygonal shield with two pores. The number of parmal pores is constantly (?) forty, as each plate possesses only two primary aspinal pores; there are no secondary or coronal pores. The numerous (between fifty and one hundred, rarely more) smaller pores between the forty parmal pores are probably always sutural pores; however, their number and position is very difficult to determine, on account of the high protecting crests; the majority of the funnel-shaped dimples between the latter seem to be blind, not perforated. Sometimes all the dimples, except the twenty spinal ones, seem to be blind and the sutural pores appear to have disappeared completely, so that there remain only twenty aspinal pores (Pl. , fig. 4).

The internal cavity of the shell in all Hexalaspida is very small, on account of the thickness of the massive wall; the latter is often greater than the diameter of the cavity. Setting aside this disproportion, the space of the cavity is further much reduced by the internal parts of the thick radial spines, which are united in the centre by their pyramidal bases (Pl. , fig. 15). Usually the twenty bases seem to remain free (supported one upon another by means of their triangular faces); but sometimes they seem to grow together perfectly and to form a single central star of acanthin. In some species, too, the sutures of the meeting branches of the apophyses of neighbouring spines seem to grow together, so that the whole shell exhibits a single piece of acanthin.

The Central Capsule of the Hexalaspida is therefore very small and seems to fill up the greatest part of the shell-cavity. Its form is constantly more or less lenticular, sometimes lentelliptical. On account of the opacity of the shell I could not make out its shape more closely.

Synopsis of the Genera of Hexalaspida.

All twenty spines externally developed, prominent on the surface of the lenticular shell. Sheaths of the spines not prominent, 376. Hexalaspis.

Sheaths of the spines prominent, 377. Hexaconus.

Only six spines (the hydrotomical spines) externally developed and prominent on the margin of the disk; the other fourteen spines not prominent. Sheaths of the spines not prominent, 378. Hexonaspis.

Sheaths of the spines prominent, 379. Hexacolpus.

All twenty spines externally developed, prominent on the surface of the lenticular shell.

Sheaths of the spines not prominent,

376. Hexalaspis.

Sheaths of the spines prominent,

377. Hexaconus.

Only six spines (the hydrotomical spines) externally developed and prominent on the margin of the disk; the other fourteen spines not prominent.

Sheaths of the spines not prominent,

378. Hexonaspis.

Sheaths of the spines prominent,

379. Hexacolpus.

Genus 376. Hexalaspis, n. gen.

Definition.—Hexalaspida with twenty prominent radial spines, which are not surrounded by prominent sheaths; the six hydrotomical spines much larger than the fourteen others.

The genus Hexalaspis is the simplest form among the Hexalaspida, and may be derived directly from Dictyaspis among the Belonaspida, by stronger development of the six hydrotomical spines. As in the following genus Hexaconus all twenty spines are prominent externally.

Subgenus 1. Hexalasparium, Haeckel.

Definition.—Six hydrotomical spines of equal size.

1. Hexalaspis heliodiscus, n. sp. (Pl. , fig. 2).

All six hydrotomical spines of nearly equal size (or sometimes the two equatorial a little larger than the four polar spines), isosceles triangular, compressed, smooth; about as long as the radius of the shell, and half as broad at the base. The fourteen other spines very small, also triangular and compressed, but little prominent on the two convex sides of the lenticular shell.

Dimensions.—Diameter of the shell 0.11; length of the six hydrotomical spines 0.05, basal breadth 0.03.

Habitat.—Central Pacific, Station 271 to 274, surface.

2. Hexalaspis stellata, n. sp.

All six hydrotomical spines of nearly equal size, lanceolate compressed, with two longitudinal furrows on each flat side, about as long as the diameter of the shell, and one-fourth as broad at the base. The fourteen other spines very thin, also compressed, half as long and only one-fourth as broad as the six large spines.

Dimensions.—Diameter of the shell 0.14; length of the six hydrotomical spines 0.13, basal breadth 0.035.

Habitat.—South Pacific, Station 284, surface.

Subgenus 2. Hexalaspidium, Haeckel.

Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

3. Hexalaspis sexalata, n. sp.

Six hydrotomical spines of unequal size; the two equatorial spines about as long as the shell-radius and twice as long as the four polar spines, which are isosceles triangular. The fourteen other spines are only half as long and one-fourth as broad as the latter, little prominent. (Resembles Hexonaspis hastata, Pl. , fig. 16, which is distinguishable by the furrows on the six spines and by the total absence of the fourteen external rudimentary spines.)

Dimensions.—Diameter of the shell 0.15; length of the two equatorial spines 0.08, of the four polar spines 0.04, of the fourteen other spines 0.02.

Habitat.—North Pacific, Station 240, surface.

4. Hexalaspis hexalastrum, n. sp.

Six hydrotomical spines of unequal size; the two equatorial spines somewhat longer than the diameter of the shell and three times as long as the four polar spines, all six triangular, smooth, of the same basal breadth (equal to half the radius). The fourteen other spines very thin, conical at the base, nearly as long as the radius.

Dimensions.—Diameter of the shell 0.21; length of the two equatorial spines 0.24, of the eighteen others 0.08 to 0.1; basal breadth of the six larger spines 0.05, of the fourteen others 0.01.

Habitat.—Western Tropical Pacific, Station 224, surface.

5. Hexalaspis hexaglypha, n. sp.

Six hydrotomical spines of unequal size; the two equatorial very large, six-sided prismatic, twice as long as the diameter of the shell and four times as long as the four pyramidal polar spines; each of these six spines with six deep furrows between the six prominent edges. The fourteen other spines very thin, compressed, two-edged, about as long as the radius of the shell.

Dimensions.—Diameter of the shell 0.11; length of the two equatorial spines 0.2, of the eighteen others 0.04 to 0.06; basal breadth of the six larger spines 0.03, of the fourteen others 0.01.

Habitat.—Tropical Atlantic, Station 352, surface.

Genus 377. Hexaconus, n. gen.

Definition.—Hexalaspida with twenty prominent radial spines, which are surrounded at the base by prominent sheaths; the six hydrotomical spines much larger than the fourteen others.

The genus Hexaconus differs from the preceding Hexalaspis in the development of conical or cylindrical sheaths surrounding the basal parts of the radial spines; these sheaths are developed sometimes around all twenty spines, sometimes only around the six larger hydrotomical spines.

Subgenus 1. Hexaconarium, Haeckel.

Definition.—Six hydrotomical spines of equal size.

1. Hexaconus ciliatus, n. sp. (Pl. , fig. 3).

All six hydrotomical spines of nearly equal size, pyramidal, with six prominent edges, somewhat longer than the radius of the shell. Sheaths sulcated, finely ciliated at the mouth, twice as broad as long and only one-fourth as long as the spines. The fourteen smaller spines very thin, bristle-shaped, shorter than the radius of the shell.

Dimensions.—Diameter of the shell 0.16; length of the six hydrotomical spines 0.11; basal breadth 0.03.

Habitat.—Central Pacific, Station 270, surface.

2. Hexaconus coronatus, n. sp. (Pl. , fig. 5).

All six hydrotomical spines of equal size, conical, somewhat compressed, with two prominent edges, scarcely as long as the radius of the shell. Sheaths crested, strongly dentated on the mouth, three times as broad as long and only one-sixth as long as the spines. Fourteen smaller spines about half as large as the six principal spines, of the same form, but without coronated sheaths.

Dimensions.—Diameter of the shell 0.2; length of the six hydrotomical spines 0.1; basal breadth 0.02.

Habitat.—North Pacific, Station 253, surface.

3. Hexaconus velatus, n. sp. (Pl. , fig. 6).

All six hydrotomical spines of equal size, conical, somewhat compressed, shorter than the radius of the shell. Sheaths very large, truncated conical, enveloping the spines almost entirely, with crested wall, only half as broad at the constricted mouth as at the base. The fourteen smaller spines about half as large as the six principal spines, of the same form, but without large sheaths.

Dimensions.—Diameter of the shell 0.12; length of the six hydrotomical spines 0.05; basal breadth 0.01.

Habitat.—North Atlantic, Station 354, surface.

Subgenus 2. Hexaconidium, Haeckel.

Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

4. Hexaconus serratus, n. sp. (Pl. , fig. 4).

Six hydrotomical spines of unequal size, the two equatorial being as long as the radius of the shell and one and a half times as large as the four polar; all of the same form, triangular, compressed, with six prominent edges. Sheaths cylindrical, half as long as the spines, with prominent crests, and with strong serrated teeth at the distal mouth. The fourteen smaller spines scarcely one-fourth or one-sixth as large as the six principal spines, without prominent sheaths.

Dimensions.—Diameter of the shell 0.2; length of the equatorial spines 0.1, basal breadth 0.05; length and breadth of the sheaths 0.05.

Habitat.—South Pacific, Station 288, surface.

5. Hexaconus vaginatus, n. sp. (Pl. , fig. 7).

Six hydrotomical spines of unequal size; the two equatorial very stout, pyramidal, six-edged, nearly as long as the diameter of the shell, and on the base three to four times as broad as the eighteen other spines, which are much thinner, all nearly of equal length, and two-edged. All twenty spines are provided with prominent basal sheaths, which are truncate conical, sulcate, and dentate on the narrowed distal mouth. The sheaths of the six hydrotomical spines are twice to three times as large as those of the fourteen smaller spines.

Dimensions.—Diameter of the shell 0.15; length of the spines 0.12; basal breadth of the equatorial spines 0.04, of the other spines 0.02; length of the hydrotomical sheaths 0.05, of the other sheaths 0.02.

Habitat.—Central Pacific, Station 274, surface.

6. Hexaconus echinatus, n. sp. (Pl. , fig. 12).

Six hydrotomical spines of unequal size; the two equatorial, and their sheaths twice as large as the four polar spines. These six spines are six-edged, pyramidal, and their basal half enveloped by very large conical sheaths which are sulcate, and twice as broad on the dentate distal mouth as on the narrower base. The other fourteen spines are very thin, two-edged, half as long, with low sheaths. Approaches some forms of Diploconus.

Dimensions.—Diameter of the shell 0.15; length of the equatorial spines 0.13, of the polar spines 0.08.

Habitat.—Indian Ocean, Belligemma, Ceylon, Haeckel, surface.

Genus 378. Hexonaspis, n. gen.

Definition.—Hexalaspida with six prominent radial spines (in the hydrotomical plane) which are not surrounded by prominent sheaths; the fourteen other spines quite rudimentary, not prominent.

The genus Hexonaspis and the following Hexacolpus differ from the two preceding genera in the rudimentary shape of the fourteen reduced and stunted smaller spines; these are only developed inside the shell, and are not prominent outside over its surface.

Subgenus 1. Hexonasparium, Haeckel.

Definition.—Six hydrotomical spines of equal size.

1. Hexonaspis heliosestrum, n. sp.

All six hydrotomical spines of nearly equal size, isosceles triangular, compressed, smooth, about as long as the diameter of the shell and three times as long as broad at the base. This species is very similar to Hexalaspis heliodiscus (Pl. , fig. 2), but differs in the larger size of the six marginal spines and in the complete external absence of the fourteen smaller spines.

Dimensions.—Diameter of the shell 0.13; length of the six marginal spines 0.12, basal breadth 0.04.

Habitat.—Tropical Atlantic, Station 348, surface.

2. Hexonaspis hexapleura, n. sp. (Pl. , fig. 15).

All six hydrotomical spines of nearly equal size, triangular, compressed, six-edged, about as long as the radius of the shell and twice as long as broad on the base. Two strong prominent ribs on each flat side of the spines. Shell very thick-walled, with a very small cavity.

Dimensions.—Diameter of the shell 0.11; length of the six marginal spines 0.06, basal breadth 0.03.

Habitat.—South Atlantic, Station 332, surface.

3. Hexonaspis hexagona, n. sp.

All six hydrotomical spines of equal size, very short, triangular, only half as long as broad at the base. The whole shell accordingly forms a regular hexagon, the six corners of which are formed by the distal points of the rudimentary spines, the six sides by their straight lateral edges. Shell very dark.

Dimensions.—Diameter of the shell 0.2; length of the six marginal spines 0.03, basal breadth 0.06.

Habitat.—South Atlantic (east of Patagonia), Station 318, surface.

Subgenus 2. Hexonaspidium, Haeckel.

Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

4. Hexonaspis hastata, n. sp. (Pl. , fig. 16).

Six hydrotomical spines of unequal size; two larger equatorial spines with six prominent wings, about as long as the radius of the shell and half as broad at the base; the four polar spines quite as broad, but only half as long, nearly equilateral triangular, with two shallow furrows on each flat side at the broader base. The fourteen smaller spines not visible on the surface, quite rudimentary. Crests of the surface elegantly denticulated.

Dimensions.—Diameter of the shell 0.14; length of the two equatorial spines 0.08, of the four polar spines 0.04; basal breadth 0.04.

Habitat.—Central Pacific, Station 271, surface.

Genus 379. Hexacolpus, n. gen.

Definition.—Hexalaspida with six prominent radial spines (in the hydrotomical plane), which are surrounded by prominent sheaths at the base; the fourteen other spines quite rudimentary, not prominent.

The genus Hexacolpus differs from the preceding Hexonaspis in the development of conical or cylindrical sheaths around the basal parts of the radial spines. It bears to the latter the same relation as Hexaconus exhibits to Hexalaspis.

Subgenus 1. Hexacolparium, Haeckel.

Definition.—Six hydrotomical spines all nearly of equal size.

1. Hexacolpus nivalis, n. sp. (Pl. , fig. 1).

Hexalaspis nivalis, Haeckel, 1882, Manuscript et Atlas.

All six hydrotomical spines of nearly equal size and equidistant, thin, lanceolate, compressed, somewhat shorter than the diameter of the hexagonal shell. Sheaths nearly prismatic, conical in the distal third, each with twelve prominent parallel crests, which are separated by twelve deep furrows; their contracted distal opening or mouth denticulate. The sheaths are as long as the radius of the shell, and envelop two-thirds of the spines. (Resembles certain forms of snow-crystals.)

Dimensions.—Diameter of the shell 0.15, thickness of its wall 0.08; length of the spines 0.1, of the sheath 0.007; breadth of the latter 0.04.

Habitat.—West Tropical Pacific, Station 225, surface.

2. Hexacolpus conifer, n. sp.

All six hydrotomical spines of equal size and equidistant, triangular, compressed, about as long as the radius of the circular shell. Sheaths conical, sulcate, half as broad on the serrate distal end as on the base. The sheaths envelop the basal half of the spines.

Dimensions.—Diameter of the shell 0.18; length of the spines 0.1, of the sheaths 0.06; basal breadth of the latter 0.07, distal breadth 0.04.

Habitat.—North Pacific, Station 236, surface.

Subgenus 2. Hexacolpidium, Haeckel.

Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.

3. Hexacolpus trypanon, n. sp. (Pl. , fig. 11).

Six hydrotomical spines of unequal size, two equatorial about as long as the diameter of the shell and nearly twice as large as the four polar; all of the same form, quadrangular prismatic, with prominent edges and pointed distal ends. Sheaths six-sided prismatic, with strong prominent edges and thinner parallel ribs between them; their distal mouth with six strong denticulated teeth. The sheaths envelop two-thirds of the spines, and are as broad as the radius of the shell.

Dimensions.—Diameter of the shell 0.13; length of the equatorial spines 0.12, of their sheaths 0.08; breadth of the latter 0.06.

Habitat.—South Pacific, Station 288, surface.

4. Hexacolpus dodecodus, n. sp.

Six hydrotomical spines of unequal size, two equatorial about as long as the radius of the shell and twice as large as the four polar; all of the same form, triangular, compressed, sulcated. Sheaths prismatic, with twelve prominent, parallel edges, and twelve strong serrated triangular teeth on the mouth. The sheaths envelop the basal half of the spines. This species greatly resembles Hexaconus serratus (Pl. , fig. 4), but differs in the larger size of the equatorial spines and the complete reduction of the fourteen smaller spines.

Dimensions.—Diameter of the shell 0.2; length of the equatorial spines 0.1, of their sheaths 0.06; breadth of the latter 0.08.

Habitat.—North Pacific, Station 248, surface.

5. Hexacolpus infundibulum, n. sp. (Pl. , fig. 10).

Six hydrotomical spines of unequal size, two equatorial about twice as long as the diameter of the shell and as the four polar spines; all six spines of the same form, quadrangular prismatic, pointed at the distal pyramidal end. Sheaths conical, two to three times as broad at the denticulate distal mouth as at the narrow base, sulcate; the mantle of the cone concavely vaulted. The large sheaths envelop two-thirds or three-fourths of the spines.

Dimensions.—Diameter of the shell 0.1 to 0.13; length of the equatorial spines 0.15 to 0.2, of their sheaths 0.1 to 0.15; basal breadth of the latter 0.04, distal breadth 0.12.

Habitat.—Central Pacific, Station 272, surface.