Definition.—Belonaspida with forty parmal pores (two on each plate), with numerous by-spines and with a network of prominent crests on the dimpled surface.
The genus Coleaspis differs from its ancestral genus Dictyaspis in the development of numerous by-spines, and bears therefore among the ellipsoidal Belonaspida the same relation to it as Hystrichaspis does to Coscinaspis among the spherical Dorataspida. If the four equatorial spines in Coleaspis become different in pairs, it passes over into Hexalaspis. The shell is usually very dark and thick-walled.
1. Coleaspis coronata, n. sp.
All twenty spines of nearly equal size and form, about as long as the radius of the shell, compressed, sword-like, two-edged; both equatorial spines of the hydrotomical axis little longer than the eighteen others. Crests between the dimples of the shell-surface dentated, forming around the basal half of each spine a cylindrical sheath with a dentated, crown-like mouth, the teeth of which are prolonged into simple by-spines. (Similar to Hexaconus coronatus, Pl. 139, fig. 5, but differing in the nearly equal size of the spines and their sheaths, and in the longer by-spines.)
Dimensions.—Major axis of the shell 0.2, minor 0.17; length of the spines 0.12, basal breadth 0.02.
Habitat.—Central Pacific, Station 266, surface.
2. Coleaspis vaginata, n. sp. (Pl. 140, fig. 13).
All twenty spines of nearly equal size and form, nearly as long as the diameter of the shell, conical; both equatorial spines of the hydrotomical axis about one-third longer than the eighteen others. Crests between the dimples of the shell-surface serrated, forming around the basal half of each spine a conical truncate sheath with crested surface and serrated mouth, the teeth of which are prolonged into short by-spines. (Similar to Hexaconus vaginatus, Pl. 139, fig. 7, but differing in the nearly equal size of all the spines and in the double thickness of the shell-wall.)
Dimensions.—Major axis of the shell 0.12, minor 0.1, length of the spines 0.08, basal breadth 0.01.
Habitat.—North Pacific, Station 253, surface.
3. Coleaspis obscura, n. sp.
All twenty spines of nearly equal size and form, little longer than their large cylindrical sheaths, which are nearly as long as the radius of the shell, and armed on the truncated mouth with strong triangular by-spines, both equatorial spines of the hydrotomical axis one and a half times as long as the eighteen others. Shell very dark and thick walled, quite opaque.
Dimensions.—Major axis of the shell 0.1, minor 0.08; length of the spines 0.06, of their sheaths 0.04.
Habitat.—Arctic Ocean, Greenland, Koch, surface.
4. Coleaspis occulta, n. sp.
All twenty spines of nearly equal size and form, quite concealed in their long cylindrical sheaths, which are somewhat longer than the radius of the shell, and armed on the truncated mouth with acute simple teeth; each sheath deeply sulcated, apparently resulting from the concrescence of numerous parallel leaf-shaped by-spines. Small shell very dark and thick-walled, quite opaque.
Dimensions.—Major axis of the shell 0.08, minor 0.06; length of the spines and their sheaths 0.05 to 0.06.
Habitat.—Antarctic Ocean (off Kerguelen), Station 159, surface.
Definition.—Both equatorial spines of the hydrotomical axis much larger and of peculiar form, different from the eighteen other spines.
5. Coleaspis amphilonche, n. sp.
Both equatorial spines of the hydrotomical axis much longer than the eighteen others, and of very different form; one and a half times as long as the diameter of the shell, prismatic, with six prominent edges, pyramidal at the distal point. The eighteen other spines triangular, compressed, two-edged, scarcely as long as the radius of the thick-walled shell. Pores of the shell irregular polygonal, separated by ciliated crests, which bear simple by-spines (one-third as long as the radius).
Dimensions.—Major axis of the shell 0.15, minor 0.12; length of the two larger spines 0.22, of the eighteen smaller 0.06 to 0.08; basal breadth of the former 0.03, of the latter 0.008.
Habitat.—South Atlantic, Station 341, surface.
6. Coleaspis hydrotomica, n. sp. (Pl. 140, fig. 14).
Both equatorial spines of the hydrotomical axis much larger than the eighteen others, and of very different form; about as long as the diameter of the shell, in the basal half four-sided pyramidal, with four thick prominent edges, in the middle part constricted, in the distal half lanceolate, two-edged. Both equatorial spines of the geotomical axis of similar form, but much smaller, scarcely one-third as long. The sixteen other spines sword-like, thin, two-edged, about as long as the radius of the thick-walled shell. Pores of the shell irregular roundish, separated by high dentated crests, which bears zigzag by-spines (half as long as the radius).
Dimensions.—Major axis of the shell 0.12, minor axis 0.1; length of the two larger spines 0.11, of the eighteen others 0.04 to 0.06; basal breadth of the former 0.04, of the latter 0.01.
Habitat.—Cape of Good Hope, Station 143, surface.
Definition.—Belonaspida with eighty to two thousand or more parmal pores (four to one hundred or more on each plate), without by-spines on the surface.
The genus Phatnaspis corresponds to the spherical Coscinaspis among the Dorataspida, and differs from the other Belonaspida in the great number of the parmal pores; whilst the four other preceding genera exhibit only two opposite aspinal pores in the centre of each plate, in this there are constantly numerous coronal pores in addition to these, and the plates always possess the characteristic form of a wainscotted or panelled work, with quadrangular meshes. The number of these parmal pores amounts in each plate to from ten to twenty, often one hundred and twenty or more; therefore the number of parmal pores in the whole shell amounts to two thousand or more. Sometimes the pores are circular, but in this case too they are surrounded by quadrangular frames. The quadrangles are sometimes quite regular squares, sometimes more or less irregular. The thin and fragile bars between the quadrangular pores form in each plate two peculiar systems of parallel crests, which cross at right angles. Commonly the parallel crests of one system (parallel to the major diameter of the compressed radial spines) are equidistant, and pierce from one edge of the plate to the opposite, whilst the parallel crests of the other system (parallel to the minor diameter of the spines) are interrupted and at different distances (Pl. 136, fig. 9); but in other species both crossed systems are quite regular. In each plate there is one primary diagonal rib (often stronger than the parallel crests) which connects the two opposite corners of the rhomboidal plate. We can distinguish in this genus three different subgenera: A. in Phatnasparium the primary diagonal rib arises from both flat sides of the compressed sword-like, radial spines; B. in Phatnasplenium from both sharp edges of them; C. in Phatnaspidium two crossed diagonal ribs arise from four edges of the spines (combination of A and B). Therefore in the first subgenus (A) two primary aspinal pores are placed opposite on the sharp edges of the spines, but in the second (B) inversely on their flat sides; in the third (C) there are apparently four primary aspinal pores, which are probably derived from B or A by division of the two pores.
Definition.—In the centre of each rhomboidal plate two primary aspinal pores, opposite on both edges of the compressed spines, from both flat sides of which the primary diagonal crest arises.
1. Phatnaspis lacunaria, n. sp. (Pl. 136, fig. 9).
Parmal pores irregular quadrangular, of unequal size and form, ten to twelve on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores opposite on both edges of the latter. Spines much compressed, sword-like, their outer half shorter than the inner.
Dimensions.—Length of the shell 0.21 to 0.23, breadth 0.18 to 0.2; basal breadth of the spines 0.01.
Habitat.—Central Pacific, Station 268, surface.
2. Phatnaspis ensiformis, n. sp.
Parmal pores irregular quadrangular, of unequal size and form, six to eight on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores opposite on the two edges of the latter. Spines very broad, strongly compressed, sword-like, their outer half larger than the inner.
Dimensions.—Length of the shell 0.16, breadth 0.11; basal breadth of the spines 0.02.
Habitat.—Tropical Atlantic, Station 348, surface.
3. Phatnaspis loculata, n. sp.
Parmal pores regular quadrangular, of nearly equal size and form, twelve to sixteen on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores on the two edges of the latter. Spines linear, compressed, very long and thin, their outer half three to four times as long as the inner.
Dimensions.—Length of the shell 0.24, breadth 0.18; breadth of the spines 0.004.
Habitat.—North Atlantic, Station 354, surface.
4. Phatnaspis fenestrata, Haeckel.
Haliommatidium fenestratum, Haeckel, 1862, Monogr. d. Radiol., p. 421.
Parmal pores regular quadrangular, of nearly equal size and form, six to eight on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary aspinal pores on the two edges of the latter. Spines linear, little compressed, or nearly needle-shaped, very long and thin, their outer half five to ten times as long as the inner.
Dimensions.—Length of the shell 0.11 to 0.12, breadth 0.07 to 0.08; breadth of the spines 0.002.
Habitat.—Mediterranean (Messina), surface.
5. Phatnaspis cristata, n. sp. (Pl. 136, fig. 6).
Parmal pores circular, of very different size, separated by high square crests, ten to twelve on each side of the high, comb-like, primary diagonal rib, which arises from both flat sides of the twoedged spines; two primary aspinal pores on the two edges of the latter. Each circular pore is surrounded by a square frame. Spines sword-like, strongly compressed, their outer part longer than the inner.
Dimensions.—Length of the shell 0.2 to 0.22, breadth 0.16 to 0.18; basal breadth of the spines 0.01.
Habitat.—North Pacific, Station 254, surface.
6. Phatnaspis coscinoides, n. sp.
Parmal pores circular, regular, all of nearly equal size, twelve to sixteen on each side of the primary diagonal rib, which arises from both flat sides of the two-edged spines; two primary pores on the two edges of the latter. Spines linear, little compressed, their outer part much longer than the inner.
Dimensions.—Length of the shell 0.18, breadth 0.15; breadth of the spines 0.006.
Habitat.—South Atlantic, Station 325, surface.
Definition.—In the centre of each rhomboidal plate two primary aspinal pores, opposite on the two flat sides of the compressed spines, from the two edges of which the primary diagonal crest arises.
7. Phatnaspis orthopora, n. sp.
Parmal pores irregular quadrangular, of unequal size and form, four to six on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two larger primary aspinal pores opposite on the two flat sides of the latter. Spines very thin and long, linear, their outer half three to four times as long as the inner.
Dimensions.—Length of the shell 0.08, breadth 0.06; breadth of the spines 0.003.
Habitat.—North Atlantic, Station 353, surface.
8. Phatnaspis polypora, n. sp.
Parmal pores irregular polygonal, of very unequal size and form, sixteen to twenty on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two very large, lanceolate, primary aspinal pores opposite on the two flat sides of the latter. Spines very thin, linear, on the outside of the shell rudimentary. (This remarkable species somewhat resembles Coscinaspis polypora, Pl. 136, fig. 8.)
Dimensions.—Length of the shell 0.32, breadth 0.24; breadth of the spines 0.002.
Habitat.—South Atlantic, Station 332, surface.
9. Phatnaspis quadratura, n. sp.
Parmal pores regular, square, all of nearly equal size and form, ten to twelve on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two primary aspinal pores opposite on the two flat sides of the latter, not different from the other pores. Spines sword-like, their outer part about as long as the inner.
Dimensions.—Length of the shell 0.2, breadth 0.16; basal breadth of the spines 0.004.
Habitat.—Central Pacific, Station 274, surface.
10. Phatnaspis tabulata, Haeckel.
Haliomma tabulatum, J. Müller, 1858, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 37, Taf. v. figs. 5-8.
Haliomma tabulatum, Haeckel, 1862, Monogr. d. Radiol., p. 429.
Parmal pores regular, circular, with square frames, all of nearly equal size, eight to ten on each side of the primary diagonal rib, which arises from both edges of the compressed spines; two primary aspinal pores opposite on the flat sides of the latter. Spines sword-like, short, scarcely half as long as the radius of the shell, their central ends are thickened and cause by their union the deceptive appearance of an enclosed "medullary shell."
Dimensions.—Length of the shell 0.12 to 0.15, breadth 0.1 to 0.12; breadth of the spines 0.006.
Habitat.—Mediterranean; Nice, Müller; Portofino, near Genoa, Haeckel, surface.
Definition.—In the centre of each rhomboidal plate four primary aspinal spines, forming a regular cross, the centre of which receives the cylindrical or four-sided prismatic spine.
11. Phatnaspis haliommidium, n. sp. (Pl. 136, fig. 7).
Parmal pores irregular quadrangular, of unequal size and form, eight to ten on each side of the crossed diagonal ribs, which arise at right angles from the four edges of the prismatic spines; four primary aspinal pores not different from the others. Outer part of the strong spines scarcely longer than the inner. (Resembling Icosaspis tabulata, Pl. 136, fig. 2, which, however, is distinguished by the spherical shell and the larger pores.)
Dimensions.—Length of the shell 0.22, breadth 0.17; breadth of the spines 0.016.
Habitat.—North Pacific, Station 244, surface.
12. Phatnaspis mülleri, n. sp.
Haliommatidium mülleri, Haeckel, 1862, Monogr. A. Radiol, p. 419, pl. xiii. figs. 10-12.
Parmal pores regular, square, all of nearly equal size and form, twelve to sixteen on each side of the crossed diagonal ribs, which arise at right angles from the needle-shaped spines; the four primary aspinal pores not different from the others. Spines very thin and long, cylindrical; four to six times longer in the outer than in the inner part.
Dimensions.—Length of the shell 0.24, breadth 0.16; breadth of the spines 0.002.
Habitat.—Mediterranean (Messina), surface.
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. 719). 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. 599). 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. 139, 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. 139, 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. 139, 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. 139, 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. 139, 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. 139, fig. 2; Pl. 140, 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. 139, 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. 139, 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. 140, 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.
| All twenty spines externally developed, prominent on the surface of the lenticular shell. | brace | 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. | brace | 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. | ||||
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.
Definition.—Six hydrotomical spines of equal size.
1. Hexalaspis heliodiscus, n. sp. (Pl. 139, 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.
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. 140, 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.
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.
Definition.—Six hydrotomical spines of equal size.
1. Hexaconus ciliatus, n. sp. (Pl. 139, 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. 139, 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. 139, 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.
Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.
4. Hexaconus serratus, n. sp. (Pl. 139, 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. 139, 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. 140, 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.
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.
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. 139, fig. 2), but differs in the larger size of the six marginal spines and in the complete external absence of the fourteen smaller spines.