Chapter XI: Literature and History (13)

_Arachnosphæra oligacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 356,
Taf. x. fig. 2, Taf. xi. fig. 3.

Innermost shell with regular, hexagonal meshes; its diameter three times as long as the equal distances between every two concentric shells. Fifteen to twenty radial spines scattered at wide intervals, each with six to eight verticils.

_Dimensions._--Diameter of the innermost shell 0.12; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Mediterranean (Messina), surface, Haeckel.

2. _Arachnosphæra myriacantha_, Haeckel.

_Arachnosphæra myriacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 357,
Taf. x. fig. 3, Taf. xi. fig. 4.

Innermost shell with regular, hexagonal meshes; its diameter twice as long as the equal distances between every two concentric shells. At each nodal-point occurs one radial spine with six to eight verticils (spines in all one hundred to one hundred and twenty or more).

_Dimensions._--Diameter of the innermost shell 0.1; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface.

{269}3. _Arachnosphæra dolichacantha_, n. sp.

Innermost shell with regular, hexagonal meshes, very small; its diameter only as long as the equal distances between every two concentric shells. At each nodal-point occurs one radial spine with twelve to sixteen verticils (altogether thirty to forty spines).

_Dimensions._--Diameter of the innermost shell 0.05; distance between the concentric shells 0.04 to 0.05.

_Habitat._--Central Pacific, Station 265 to 274, surface.

4. _Arachnosphæra increscens_, n. sp.

Innermost shell with regular, hexagonal meshes; its diameter three times as long as the distance between it and the second shell, quite as long as the distance between the fifth and sixth shells; the distances between the concentric shells gradually increasing from the centre. Radial spines about fifty to sixty, each with six to eight verticils.

_Dimensions._--Diameter of the innermost shell (A) 0.75; distances between the following shells--A, B = 0.025, B, C = 0.037, C, D = 0.05, D, E = 0.062, E, F = 0.075, &c.

_Habitat._--Central Pacific, Station 271, surface.

Subgenus 2. _Arachnosphæromma_, Haeckel.

_Definition._--Pores of the innermost shell irregular, polygonal.

5. _Arachnosphæra tenuissima_, n. sp.

Innermost shell with irregular, polygonal meshes; its diameter twice as long as the equal distance between every two concentric shells. Forty to fifty radial spines, each with twelve to sixteen verticils.

_Dimensions._--Diameter of the innermost shell 0.1, distance between the concentric shells 0.04 to 0.05.

_Habitat._--South Atlantic, Station 332, surface.

6. _Arachnosphæra velaris_, n. sp.

Innermost shell with irregular, polygonal meshes; its diameter twice as long as the distance between it and the second shell, quite as long as the distance between the third and fourth shells; the distance between the concentric shells gradually increasing from the centre. Radial spines twenty to thirty, each with ten to twelve verticils.

_Dimensions._--Diameter of the innermost shell (A) 0.5; distances of the following shells--A, B = 0.025, B, C = 0.037, C, D = 0.05, D, E = 0.062, E, F = 0.075.

_Habitat._--Tropical Atlantic, Station 347, surface.

{270}Subfamily SPONGIOMMIDA,[149] Haeckel.

_Definition._--#Astrosphærida# with spongy spherical or polyhedral shell (with or without enclosed concentric lattice-shells).

Genus 111. _Spongiomma_,[150] n. gen.

_Definition._--#Astrosphærida# with solid spongy sphere, with numerous simple radial spines, but without latticed medullary shells.

The genus _Spongiomma_ differs from its ancestral form, _Styptosphæra_, in the development of simple radial spines on the surface of the solid sphere, the entire mass of which is composed of an irregular, spongy wicker-work.

Subgenus 1. _Spongiommella_, Haeckel.

_Definition._--Radial spines on the surface of the spongy sphere all of the same shape.

1. _Spongiomma radiatum_, n. sp.

Spongy framework of the solid sphere of the same structure throughout, with small, irregular, polyhedral meshes and very thin thread-like bars. From the surface arise very numerous (one hundred and twenty to one hundred and sixty or more) straight, bristle-shaped radial spines, as long as the radius of the sphere (counting from the middle part of it).

_Dimensions._--Diameter of the spongy sphere 0.2; length of the radial spines 0.1.

_Habitat._--Central Pacific, Station 272, surface.

2. _Spongiomma denticulatum_, n. sp.

Spongy framework of the solid sphere of the same structure throughout, with small, almost equal meshes, four to eight times as broad as the thin, elegantly denticulated bars; from the surface arise very numerous (two hundred to three hundred or more) curved, radial spines, as long as the radius, and of the same form as the bars.

_Dimensions._--Diameter of the sphere 0.25; length of the spines 0.12.

_Habitat._--Central Pacific, Station 274, surface.

3. _Spongiomma spathillatum_, n. sp.

Spongy framework in the central part of the sphere much denser and darker, and with smaller meshes than in the peripheral part in which are very thin bars. Entire surface covered with {271}innumerable short, bristle-shaped radial spines, only one-eighth as long as the radius, of the same elegant form as in _Octodendron spathillatum_ (Pl. 18, figs. 2, 4); each spine developed in a zig-zag fashion, with very small beards, with a delicate spathillum (or coronal of beard spines) at the distal end.

_Dimensions._--Diameter of the spheres 0.16; length of the spines 0.01.

_Habitat._--South Pacific, Station 295, surface.

4. _Spongiomma clavatum_, n. sp.

Spongy framework in the central part of the sphere much denser and darker than in the peripheral part. On the surface are sixty to eighty stout, club-shaped radial spines, as long as the radius of the sphere, in the proximal half three-sided prismatic, with three dentated edges; they begin at the middle of the radius (where the denser inner framework changes into the looser outer) and are very thin at first but increase slowly in thickness towards the truncated distal end. (Similar to _Centrocubus rhopalophorus_, Pl. 18, fig. 1, but without the cubical medullary shell.)

_Dimensions._--Diameter of the sphere 0.4; length of the spines 0.2.

_Habitat._--North Pacific, Station 241, surface.

Subgenus 2. _Spongiommura_, Haeckel.

_Definition._--Radial spines on the surface of the spongy sphere of two different kinds; large main spines and small by-spines.

5. _Spongiomma helioides_, n. sp.

Spongy framework of the sphere everywhere of the same structure, with almost equal meshes, ten to twelve times as broad as the bars. Sixteen to twenty radial main spines, longer than the shell diameter, three-sided prismatic, with three serrated edges, beginning about the middle of the radius and increasing in thickness to the truncated distal end. Between them occur numerous thin, bent, bristle-shaped by-spines. (Very similar to _Spongosphæra helioides_, Monogr. d. Radiol., Taf. xii. figs. 11-13, but without medullary shells.)

_Dimensions._--Diameter of the sphere 0.3; length of the main spines 0.4, of the by-spines 0.01.

_Habitat._--Tropical Atlantic, Station 352, surface.

6. _Spongiomma multiaculeum_, Haeckel.

_Spongechinus multiaculeatus_, Dunikowski, 1882, Denkschr. d. k. Akad. d.
Wiss. Wien, Bd. xlv. p. 29, Taf. v. figs. 60-63.

Spongy framework of the sphere very compact, with small meshes, scarcely broader than the bars; four to eight large main spines, three-sided pyramidal, longer than the shell radius; numerous (thirty to forty) thin by-spines, scarcely half as long.

{272}_Dimensions._--Diameter of the sphere 0.16; length of the main spines 0.11, of the by-spines 0.03.

_Habitat._--Fossil in the Alpine Jura, Schafberg near Salzburg (Dunikowski).

7. _Spongiomma asteroides_, n. sp.

Spongy framework in the central part of the sphere much denser and darker than in the peripheral part. Sixty to eighty cylindro-conical main spines, as long as the radius, between them are numerous straight, bristle-shaped by-spines half that length.

_Dimensions._--Diameter of the sphere 0.28; length of the main spines 0.16, of the by-spines 0.08.

_Habitat._--South Atlantic, Station 325, surface.

Genus 112. _Spongodrymus_,[151] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with solid spongy sphere, without latticed medullary shell, with numerous branched radial spines.

The genus _Spongodrymus_ differs from the preceding _Spongiomma_ in the ramification of the numerous radial spines, covering the surface of the solid spongy sphere.

1. _Spongodrymus elaphococcus_, n. sp. (Pl. 18, fig. 9).

Spongy framework of the solid sphere equal throughout, on the surface arising in the form of very numerous (sixty to eighty or more) spongy cones with rather rhomboidal meshes. Each cone is prolonged into a very thin, irregularly curved radial spine, which is twice as long as the shell diameter, simple in the proximal half, branched like a tree in the distal half; each arborescent spine has from sixteen to thirty-two terminal branches, which fall in one spherical face. The branches of neighbouring spines are partly connected by anastomoses, so that they begin to form an outer spherical shell (cortical shell) with a looser spongy framework.

_Dimensions._--Diameter of the whole spherical skeleton (sphere formed by the distal ends of the dichotomous branches) 0.9, of the inner solid spongy sphere 0.02.

_Habitat._--Tropical Atlantic, Station 349, surface.

2. _Spongodrymus abietinus_, n. sp.

Spongy framework denser and darker in the central part of the sphere than in the peripheral part, with rather coarse meshes and thick bars. From the surface arise very numerous (sixty to eighty) stout, radial branches, as long as the shell radius, branched like a pine tree (with six to twelve ramified branches). Similar in structure to _Cromyodrymus abietinus_ (Pl. 30, fig. 6), but with a quite irregular spongy texture in the central sphere.

_Dimensions._--Diameter of the sphere 0.3; length of the spines 0.015.

_Habitat._--Central Pacific, Station 272, surface.

{273}Genus 113. _Spongechinus_,[152] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with hollow, spongy sphere, without latticed medullary shell in the central cavity, and with numerous simple radial spines.

The genus _Spongechinus_ differs from its ancestral form, _Plegmosphæra_, in the development of numerous radial spines on the surface of the spongy sphere, within which is enclosed a large spherical central cavity.

1. _Spongechinus setosus_, n. sp.

Spongy sphere three times as broad as its inner cavity, with a very delicate, equal framework. Entire surface covered with short, straight, bristle-shaped radial spines, about half as long as the radius.

_Dimensions._--Diameter of the sphere 0.2, of its inner cavity 0.07; length of the spines 0.05.

_Habitat._--North Atlantic, Azores, surface.

2. _Spongechinus serrulatus_, n. sp.

Spongy sphere twice as broad as its inner cavity, with a delicate, equal framework. Entire surface covered with short, curved, radial spines, which are elegantly denticulated, and as long as the shell radius.

_Dimensions._--Diameter of the sphere 0.3, of its cavity 0.15; length of the spines 0.15.

_Habitat._--Central Pacific, Station 274, surface.

3. _Spongechinus cavus_, n. sp.

Spongy sphere only one-fourth broader than the large inner cavity, its spongy wall being only one-fourth as thick as the radius, composed of three to four strata of irregular, small meshes. Surface covered with short, bristle-shaped, curved spines, one-third as long as the radius.

_Dimensions._--Diameter of the sphere 0.5, of its inner cavity 0.4; length of the spines 0.08.

_Habitat._--North Atlantic, Station 354, surface.

Genus 114. _Spongothamnus_,[153] n. gen.

_Definition._--#Astrosphærida# with hollow, spongy sphere, without latticed medullary shell in the central cavity, and with numerous branched radial spines.

The genus _Spongothamnus_ differs from the preceding _Spongechinus_ in the ramification of the numerous radial spines, covering the surface of the hollow spongy sphere; {274}it therefore exhibits the same relation to the latter that _Spongodrymus_ bears to _Spongiomma._

1. _Spongothamnus furcatus_, n. sp.

Spongy sphere twice as broad as its inner cavity, with very delicate bars, and irregular, dense framework. From the surface arise one hundred and fifty to one hundred and eighty thin, forked, bristle-shaped spines, half as long as the radius; both fork branches one-third as long as the basal or simple part.

_Dimensions._--Diameter of the sphere 0.3, of its inner cavity 0.15; length of the spines 0.08.

_Habitat._--North Pacific, Station 241, surface.

2. _Spongothamnus scoparius_, n. sp.

Spongy sphere four times as broad as its inner cavity, with thick bars and rather loose framework. From the surface arise sixty to eighty broom-shaped radial spines, as long as the radius, each in the basal half simple, in the distal half with six to twelve irregularly ramified branches (similar to the spines of _Cromyodrymus abietinus_, Pl. 30, fig. 6).

_Dimensions._--Diameter of the sphere 0.4, of the inner cavity 0.1; length of the spines 0.2.

_Habitat._--Central Pacific, Station 271, surface.

Genus 115. _Spongopila_,[154] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with a single, spherical, latticed medullary shell, immediately enveloped by the spongy framework of the cortical shell; on the surface of the latter are numerous radial spines.

The genus _Spongopila_ is a _Spongoplegma_ with radial spines. On the other hand it may be derived either from _Elaphococcus_, by communication of the branched spines, or from _Arachnosphæra_, by development of spongy branches between the concentric spheres.

1. _Spongopila dichotoma_, n. sp.

Medullary shell with regular, hexagonal meshes, six times as broad as the bars. From each nodal-point (between every three meshes) arises a bristle-shaped radial spine, which is dichotomously branched. By communication of the neighbouring branches the loose spongy framework of the spherical cortical shell is formed, which is four times as broad as the medullary shell. On the surface occur very numerous bristle-shaped radial spines, as long as the diameter of the medullary shell. (May be derived from _Elaphococcus_.)

_Dimensions._--Diameter of the spongy cortical shell 0.3, of the medullary shell 0.08.

_Habitat._--Tropical Atlantic, Station 347, surface.

{275}2. _Spongopila verticillata_, n. sp.

Medullary shell with regular, hexagonal meshes, four times as broad as the bars. From its surface arise forty to sixty, three-sided prismatic radial spines, bearing eight to ten verticils of lateral branches, each verticil with six forked branches (two from each edge). By irregular ramification of these branches, and communication in all directions, the loose spongy framework of the cortical shell originates, which is six times as broad as the medullary shell. The free distal ends of the spines are as long as the shell radius. (May be derived from _Arachnosphæra_.)

_Dimensions._--Diameter of the spongy cortical shell 0.6, of the medullary shell 0.1.

_Habitat._--Tropical Pacific, Station 200, surface.

Genus 116. _Rhizoplegma_,[155] Haeckel, 1881, Prodromus, p. 456.

_Definition._--#Astrosphærida# with a single, spherical, latticed medullary shell, which is not armed with by-spines, but connected by stout radial main spines with the spongy cortical shell.

The genus _Rhizoplegma_ is immediately allied to the foregoing _Spongopila_, but differs from it in the large interval separating both shells. In this interval lies the wall of the central capsule, which is only pierced by the radial spines connecting both shells.

Subgenus 1. _Rhizoplegmarium_, Haeckel.

_Definition._--No free lateral branches of the radial spines between the two shells.

1. _Rhizoplegma polyacanthum_, n. sp.

Spongy cortical shell with a very fine dense framework and nearly smooth surface (without superficial by-spines). Its inner cavity is four times as broad as the medullary shell, which exhibits regular, hexagonal meshes. Radial spines sixty to eighty, three-sided prismatic, with three smooth edges, without lateral branches between both shells; their free outer part as long as the shell radius.

_Dimensions._--Diameter of the spongy cortical shell 0.3, of its inner cavity 0.2, of the medullary shell 0.05.

_Habitat._--Central Pacific, Station 274, surface.

2. _Rhizoplegma spirale_, n. sp.

Spongy cortical shell with a very delicate loose framework and bristly surface. Its inner cavity three times as broad as the medullary shell, which exhibits regular, hexagonal meshes. {276}Radial spines thirty to forty, prismatic, with three smooth, spirally contorted edges, without lateral branches between the two shells; their free outer part half as long as the shell radius.

_Dimensions._--Diameter of the spongy cortical shell 0.2, of its inner cavity 0.12, of the medullary shell 0.04.

_Habitat._--Central Pacific, Station 265, surface.

3. _Rhizoplegma trigonacantha_, n. sp.

Spongy cortical shell with a rather loose framework and coarse bars, with nearly smooth surface (without by-spines). Its inner cavity twice as broad as the medullary shell, which exhibits irregular, roundish pores. Radial spines forty to sixty, prismatic, with three smooth straight edges, without free branches between the two shells; their outer pyramidal part only one-third of the shell radius. (Very similar to the common _Rhizosphæra trigonacantha_, but with simple medullary shell.)

_Dimensions._--Diameter of the spongy shell 0.2, of its inner cavity 0.16, of the medullary shell 0.08.

_Habitat._--North Atlantic, Station 353, surface.

Subgenus 2. _Rhizoplegmidium_, Haeckel.

_Definition._--Between the two shells free lateral branches arise from the three edges of the radial spines.

4. _Rhizoplegma radicatum_, n. sp. (Pl. 15, figs. 9, 9_a_).

Spongy cortical shell with a very loose framework; on the surface are innumerable thin, forked, or repeatedly dichotomous by-spines. Its inner cavity three times as broad as the medullary shell, which exhibits regular, hexagonal meshes (fig. 9_a_). Radial spines twelve, prismatic, with straight dentated edges, their outer pointed part as long as the shell radius. Each spine between the two shells has a verticil of three forked lateral branches (fig. 9_a_). The central capsule completely distends the medullary shell, and forces out through each mesh a hernia-shaped process (fig. 9).

_Dimensions._--Diameter of the spongy shell 0.5, of its inner cavity 0.25, of the medullary shell 0.08.

_Habitat._--Central Pacific, Station 271, surface.

5. _Rhizoplegma lychnosphæra_, n. sp. (Pl. 11, fig. 5).

_Lychnosphæra rhizoplegma_, Haeckel, 1879, Atlas (pl. xi. fig. 5).

Spongy cortical shell with a very loose framework, composed of long thin beams as in _Lychnosphæra regina_ (Pl. 11, figs. 1-4). Surface covered with short bristles. Its inner cavity six times as broad as the medullary shell, which exhibits regular, hexagonal meshes. Radial spines twelve, prismatic, with three smooth edges; their outer pointed part half as long as the shell radius. Each spine has three verticils of three forked branches; the first verticil is free {277}between the two shells, while the two following verticils, by communication of their ramules, form the irregular framework. Central capsule with many herniæ, forced out through the meshes of the medullary shell (fig. 5).

_Dimensions._--Diameter of the spongy shell 0.7, of its inner cavity 0.45, of the medullary shell 0.07.

_Habitat._--South Pacific, Station 284, surface.

Genus 117. _Lychnosphæra_,[156] Haeckel, 1881, Prodromus, p. 453.

_Definition._--#Astrosphærida# with a single, spherical, latticed medullary shell, which is armed with free radial by-spines, and connected by stout radial main spines with the spongy cortical shell.

The genus _Lychnosphæra_, known only by one single, large, and very remarkable species, mainly differs from the foregoing in the development of free radial by-spines on the surface of the medullary shell, and in the free interval between it and the cortical shell; but beyond this the loose spongy framework of the latter exhibits a very remarkable structure, figured in Pl. 11.

1. _Lychnosphæra regina_ (Pl. 11, figs. 1-4).

Medullary shell (fig. 3) with regular, circular, hexagonally framed pores, twice as broad as the bars; from each hexagon-corner arises a radial, bristle-shaped by-spine, as long as the diameter. Twelve radial main spines each as broad as one of the meshes, three-sided prismatic, six to eight times as long as the medullary shell. From their three leaf-shaped (often somewhat denticulated or spirally contorted) edges arise four verticils of lateral branches, each composed of three forked, thin branches. The forked branches of the first verticil end free between the two shells (figs. 2, 3), while the two following verticils are ramified, and, by anastomosis of their branches, compose the loose spongy framework of the cortical shell. On the surface of the latter arise numerous radial (zig-zag-shaped) by-spines. The fourth verticil is terminal, with three shorter, thicker, dentated, simple branches, which constitute, together with the distal apex of the spine itself, a bunch of four terminal spines. The large central capsule completely distends the medullary shell, and forces out by its pores numerous club-shaped herniæ (fig. 1).

_Dimensions._--Diameter of the spongy cortical shell 0.6, of its inner cavity 0.4, of the central capsule 0.22, of the medullary shell 0.06; length of the radial spines 0.4, breadth 0.01.

_Habitat._--Central Pacific, Station 271, surface.

Genus 118. _Centrocubus_,[157] n. gen.

_Definition._--#Astrosphærida# with a single, cubical medullary shell, immediately surrounded by the spongy framework of the cortical shell; from the eight corners {278}of the central cube arise eight primary radial spines, and often others from the framework between them.

The genus _Centrocubus_ and the following closely allied _Octodendron_ may represent a peculiar small group of Spongiommida, remarkable for the regular, cubical form of the medullary shell, which is composed of twelve thin rods, corresponding to the twelve edges of a mathematical cube; from the eight corners invariably arise eight primary radial spines, the branches of which form the spongy cortical shell.

1. _Centrocubus octostylus_, n. sp.

Radial spines eight, arising from the eight corners of the cubiform, regular, medullary shell, gradually increasing in thickness towards the club-shaped distal end, which is five to six times as broad as the central end. From the three denticulate edges of each spine arise six to eight lateral branches, which ramify irregularly and form by their anastomosis the spongy framework which is of nearly similar structure throughout, and with large loose meshes. The free distal part of each spine is half as long as the enclosed part.

_Dimensions._--Diameter of the sphere 0.6, of the central cube 0.02; length of the spines 0.15, distal thickness 0.02.

_Habitat._--Central Pacific, Station 271, surface.

2. _Centrocubus cladostylus_, n. sp. (Pl. 18, fig. 1).

Radial spines thirty-two, club-shaped, at the distal end eight to ten times as broad as at the basal end. Eight primary spines arise from the eight corners of the regular, cubiform medullary shell, and from these, in the form of lateral branches, twenty-four secondary spines arise with concavely curved bases (three from the three denticulate edges of each spine, at nearly equal distances from the centre). The free distal end of each of the thirty-two spines is of the same shape, about half as long as the radius of the spongy sphere; framework much looser in the outer than in the inner part.

_Dimensions._--Diameter of the sphere 0.8, of the central cube 0.02; length of the spines 0.2, distal thickness 0.02.

_Habitat._--North Pacific, Station 256, surface.

3. _Centrocubus polystylus_, n. sp.

Radial spines sixty to eighty, club-shaped, four to six times as broad at the distal as at the basal end. Eight primary spines arise from the eight corners of the regular, cubiform medullary shell, the remainder either springing as lateral branches from the three denticulate corners of the former, or arising within the spongy framework, which is much denser and darker in the central than in the peripheral part. The free distal end of each spine is one-third as long as the radius.

{279}_Dimensions._--Diameter of the sphere 0.9, of the central cube 0.02; length of the spines 0.15, distal thickness 0.02.

_Habitat._--South Pacific, Station 295, surface.

Genus 119. _Octodendron_,[158] n. gen.

_Definition._--#Astrosphærida# with a single, cubical medullary shell, and eight primary radial spines arising from its eight corners; these are connected at equal distances by a latticed, spherical, cortical shell, from which the spongy framework directly springs; often from the latter secondary radial spines arise.

The genus _Octodendron_ has the same regular, cubical medullary shell as the preceding _Centrocubus_, but differs from it in the wide interval separating the medullary shell from the inner spherical face of the spongy cortical shell, the two being connected only by eight radial beams, arising from the eight corners of the cube.

Subgenus 1. _Octodendridium_, Haeckel.

_Definition._--Only eight primary radial spines, arising from the eight corners of the central cube.

1. _Octodendron cubocentron_, n. sp. (Pl. 18, fig. 3).

Radial spines eight, club-shaped, with three denticulate, straight edges, twice as long as the diameter of the central cavity of the cubical spongy shell; the inner face of the latter (or the "inner cortical shell") exhibits the form of a large cube, the spongy sides of which are parallel with the simple square sides of the central cube. The thin eight radial beams, connecting the corresponding corners of both cubes, are not thicker than the edge-bars of the central cube, whilst their outer prolongations are much thicker, with four to six verticils of lateral branches. Surface of the thin walled, loose, spongy shell armed with short simple thorns.

_Dimensions._--Diameter of the spongy shell 0.2, of its inner cavity 0.1, of the central cube 0.02; length of the spines 0.2 (from the centre 0.3).

_Habitat._--Central Pacific, Station 266, surface.

2. _Octodendron spirale_, n. sp.

Radial spines eight, three-sided prismatic, three times as long as the diameter of the inner shell-cavity; their three edges denticulated and spirally contorted around the spine axis. Thickness of the loose spongy shell-wall equal to the radius of the inner cavity, three times as large as the central cube. Surface covered, with numerous thin, bristle-shaped, bent spinules.

{280}_Dimensions._--Diameter of the spongy shell 0.24, of its inner cavity 0.12, of the central cube 0.02; length of the spines 0.4, breadth 0.01.

_Habitat._--North Pacific, Station 254, surface.

3. _Octodendron pinetum_, n. sp.

Radial spines eight, three-sided prismatic, three to four times as long as the diameter of the inner shell-cavity, with three spirally contorted edges. From each spine arise at equal distances (equal to the half radius of the cavity) fifteen to twenty verticils of branches which increase in size from the base of the spine. Each verticil is composed of six forked branches (two from each spine-edge); the inferior are richly branched, and form by their connection the loose network of the spongy cortical shell, the surface of which is covered with numerous bent threads. Each spine bears a resemblance to a pine tree.

_Dimensions._--Diameter of the spongy shell 0.3, of its inner cavity 0.15, of the central cube 0.02; length of the spines 0.5 to 0.6, breadth 0.01.

_Habitat._--Central Pacific, Station 272, surface.

4. _Octodendron araucaria_, n. sp.

Radial spines eight, three-sided prismatic, with three spirally contorted edges, eight to ten times as long as the diameter of the inner shell-cavity (the free distal portion twice to three times as long). From each spine arise at equal distances thirty to thirty-five verticils of branches, which decrease in size towards the distal end. Each verticil is composed of six forked branches (two from each spine-edge); the inferior are richly ramified and form by their connection the loose spongy framework; the distal branches bear on the free end elegant spathillæ (as in the following species). Surface covered with innumerable straight bristles, as long as the cavity radius, and ending with a spathilla. Diameter of the central capsule about equal to the radius of the spongy sphere, its membrane is double-edged.

_Dimensions._--Diameter of the spongy shell 1.4 mm., of its inner cavity 0.14, of the central cube 0.02, of the central capsule 0.5 to 0.6; length of the spines 0.9 to 1.2, breadth 0.02.

_Habitat._--South Pacific, Station 288, surface.

5. _Octodendron spathillatum_, n. sp. (Pl. 18, figs. 2, 4).

Radial spines eight, three-sided prismatic, with contorted edges, five to eight times as long as the diameter of the shell-cavity (the free part twice as long). From each spine arise ten to twelve verticils of lateral branches; each verticil composed of three forked branches. The proximal larger branches ramify richly, and form by their connection the loose spongy framework of the spherical shell; the distal smaller branches are simple or bifurcated, and the ramules are provided with an elegant spathillum at the end (fig. 4). Entire surface of the spongy sphere covered with innumerable bristle-shaped radial spines (half as long as the cavity radius), zig-zag, bent, with beards, and with a spathillum at the end.

{281}_Dimensions._--Diameter of the spongy sphere 1 mm., of its central cavity 0.15, of the central cube 0.02; length of the spines 1 to 1.2 mm., breadth 0.008.

_Habitat._--Central Pacific, Station 271, surface.

Subgenus 2. _Octodendronium_, Haeckel.

_Definition._--Radial spines thirty-two or more, eight primary (arising from the eight corners of the central cube) and twenty-four or more secondary (between them).

6. _Octodendron verticillatum_, n. sp.

Radial spines thirty-two, with three denticulate straight edges, six to eight times as long as the diameter of the shell-cavity; the distal parts half free. Eight primary spines arise from the eight corners of the central cube, twenty-four secondary from the edges of these (a verticil of every three from each primary spine). Distal free parts of all thirty-two spines equal. Each spine with eight to ten verticils of forked lateral branches, without spathillæ. Surface of the spongy sphere covered with short simple bristles.

_Dimensions._--Diameter of the spongy shell 0.3, of its cavity 0.12, of the central cube 0.02; length of the spines 0.7 to 1 mm., breadth 0.02.

_Habitat._--South Pacific, Station 291, surface.

7. _Octodendron contortum_, n. sp.

Radial spines thirty-two, disposed in a similar manner to those of the former species (eight primary and twenty-four secondary); also the spongy shell of the same shape. The difference arises in the form of the spines, the three edges of which are much broader and spirally contorted around the axis; and thus the corresponding branches of the verticil do not lie in the same meridian-plane, but alternate one with another.

_Dimensions._--Diameter of the spongy shell 0.4, of its cavity 0.1, of the central cube 0.02; length of the spines 0.8 to 1.2, breadth 0.04.

_Habitat._--Central Pacific, Station 274, surface.

8. _Octodendron arboretum_, n. sp.

Radial spines sixty to ninety, three-sided prismatic, with spirally contorted and denticulate edges, six to eight times as long as the diameter of the inner shell-cavity. Eight primary arise from the eight corners of the central cube, twenty-four others from their three edges (as in the two former species); the remaining thirty to sixty spines seem to arise between the former and immediately from the dense spongy framework, which is twice as thick as the diameter of the inner shell-cavity. The numerous verticils of the free distal part are of equal shape in all the spines, composed of three forked branches in the terminal, and of more ramified branches in the inferior parts. Entire surface of the spongy shell covered with simple radial bristles, without spathillæ.

{282}_Dimensions._--Diameter of the spongy shell 0.75, of its central cavity 0.15, of the central cube 0.02; length of the spines 0.9 to 1.2, breadth 0.02.

_Habitat._--Tropical Pacific, Station 225, surface.

Genus 120. _Spongosphæra_,[159] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 54.

_Definition._--#Astrosphærida# with two concentric latticed medullary shells, connected by radial beams; the outer is immediately enveloped by the spongy framework, and bears numerous radial spines.

The genus _Spongosphæra_ (in the definition here restricted) differs from _Spongopila_ in the double medullary shell, which in the latter is simple; it exhibits to the latter the same relation that _Spongodictyon_ among the Liosphærida bears to _Spongoplegma_. The outer medullary shell of _Spongosphæra_ is immediately enveloped by the spongy wicker-work, which everywhere pierces the wall of the central capsule.

1. _Spongosphæra streptacantha_, Haeckel.

_Spongosphæra streptacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 455,
Taf. xxvi. figs. 1-3.

Spongy shell of polyhedric, irregular outline, the framework being prolonged sheath-like into the eight to twelve radial spines, which are quite irregularly distributed, very large, three-sided prismatic, with three serrated, spirally contorted edges; their length is twice to four times as great as the diameter of the spongy body; they arise with thinner bases from the outer medullary shell, which is three times as broad as the inner, both having roundish pores, twice to four times as broad as the bars; surface without radial by-spines.

_Dimensions._--Diameter of the spongy shell 0.2 to 0.6, outer medullary shell 0.04 to 0.06, inner 0.012 to 0.016.

_Habitat._--Cosmopolitan; common in all warmer seas, surface.

2. _Spongosphæra polyacantha_, J. Müller.

_Spongosphæra polyacantha_, J. Müller, 1858, Abhandl. d. k. Akad. d.
Wiss. Berlin, p. 32, Taf. iv. figs. 1-4.

Spongy shell spherical, with ten to twenty large radial spines, which arise with thinner bases from the medullary shell, and are prominent on the surface at different lengths; they are three-sided prismatic (not four-sided), with three leaf-shaped straight edges. Whilst the spongy framework is much looser than in the preceding species, both medullary shells have nearly the same shape.

_Dimensions._--Diameter of the spongy shell 0.2 to 0.5, outer medullary shell 0.04 to 0.06, inner 0.012 to 0.016.

_Habitat._--Mediterranean (Nice); Atlantic, Station 353, surface.

{283}Subgenus _Spongosphæromma_, Haeckel.

_Definition._--Radial spines on the surface of the spongy shell of two different kinds; large piercing main spines and small superficial by-spines.

3. _Spongosphæra helioides_, Haeckel.

_Spongosphæra helioides_, Haeckel, 1862, Monogr. d. Radiol., p.456, Taf.
xii. figs. 11-13.

Spongy shell spherical, with numerous curved, bristle-shaped by-spines on the surface, as long as the radius. Main spines ten to twenty, irregularly disposed, prismatic, with three dentated, spirally contorted edges, broader toward the distal end. Outer medullary shell three times as broad as the inner, with polygonal meshes (of the same size as those in the spongy framework) and fine bars.

_Dimensions._--Diameter of the spongy shell 0.2, outer medullary shell 0.02, inner 0.007.

_Habitat._--Mediterranean (Messina).

4. _Spongosphæra quadricuspis_, n. sp.

Spongy shell spherical, with numerous curved, bristle-shaped by-spines on the surface, half as long as the radius. Main spines twenty to thirty, irregularly disposed, prismatic, with three dentated, spirally contorted edges, and at the distal end four strong pyramidal divergent teeth (three as terminations of the edges, the fourth as end of the spine axis). Outer medullary shell twice as broad as the inner, both having circular, regular pores, twice to three times as broad as the bars.

_Dimensions._--Diameter of the spongy shell 0.3, outer medullary shell 0.04, inner 0.013.

_Habitat._--Central Pacific, Station 272, surface.

Genus 121. _Rhizosphæra_,[160] Haeckel, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 840.

_Definition._--#Astrosphærida# with two concentric latticed medullary shells, connected by radial beams; from the outer arise numerous radial spines, which at equal distances are connected by a latticed spherical cortical shell, surrounded by a spongy framework.

The genus _Rhizosphæra_ exhibits the same relation to _Spongosphæra_ that _Rhizoplegma_ bears to _Spongopila_; but in the latter the latticed medullary shell is simple, in the two former double. The wall of the central capsule is pierced only by the radial spines connecting the medullary and the cortical shells.

1. _Rhizosphæra trigonacantha_, Haeckel.

_Rhizosphæra trigonacantha_, Haeckel, 1862, Monogr. d. Radiol., p. 452,
Taf. xxv. figs. 1-7.

Central cavity of the spongy cortical shell twice as broad as the diameter of the outer medullary shell. Bars of all three shells of the same breadth as the thirty to fifty (or more) radial spines, {284}which are three-sided prismatic; their outer free distal end only as long as the diameter of the inner medullary shell.

_Dimensions._--Diameter of the spongy shell 0.25, of its inner cavity 0.2, outer medullary shell 0.1, inner 0.05.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Indian, Pacific, surface from many Stations.

2. _Rhizosphæra serrata_, n. sp. (Pl. 18, figs. 5-7).

Central cavity of the spongy shell five times as broad as the diameter of the outer medullary shell. Bars of all three shells of the same breadth as the forty to sixty (or more) thin radial beams between them. These are three-sided prismatic, with denticulate edges, scarcely half as broad as their outer prolongations, which are half as long as the shell radius, and possess three spirally contorted serrated edges. (The figured specimen is a young one; in the older specimens the spongy framework of the cortical shell is much more developed.)

_Dimensions._--Diameter of the spongy shell 0.3, of its central cavity 0.22, outer medullary shell 0.06, inner 0.02.

_Habitat._--Central Pacific, Stations 270 to 274, surface.

3. _Rhizosphæra leptomita_, Haeckel.

_Rhizosphæra leptomita_, Haeckel, 1862, Monogr. d. Radiol., p. 453, Taf.
xxv. figs. 8-10.

Central cavity of the spongy cortical shell twice as broad as the diameter of the outer medullary shell; bars of both very thin, only one-third as broad as the bars of the inner medullary shell. Radial spines thirty to fifty (or more), curved, three-sided prismatic; inside the spongy shell as thin as their bars, outside three times as broad.

_Dimensions._--Diameter of the spongy shell 0.27, of its inner cavity 0.2, outer medullary shell 0.1, inner 0.05.

_Habitat._--Mediterranean (Messina); Atlantic, Stations 348 to 354, surface.

----

Suborder PRUNOIDEA, Haeckel, 1883 (Pls. 13-17, 39, 40).

_Definition._--SPUMELLARIA with an ellipsoidal or cylindrical central capsule, prolonged into one axis (sometimes articulate by annular transverse strictures); with an ellipsoidal or cylindrical, fenestrated siliceous shell (often articulate by annular strictures), invariably prolonged into one axis. Fundamental form monaxon, usually with the poles of the prolonged dimensive main axis equal.

The suborder #Prunoidea# comprises those SPUMELLARIA in which the fenestrated spherical shell appears prolonged into one axis. The geometric fundamental form of the shell, which in the #Sphæroidea# was a sphere, in this case therefore becomes an ellipsoid, and whilst in the former all axes originally have the same value (Homaxonia), {285}here one main axis is constantly larger than all other axes (Monaxonia). Usually both poles of this main axis are equal (Haplopola); but in some genera both poles become different (Diplopola).

In the #Sphæroidea# all planes going through the centre of the shell are circular, whereas in the #Prunoidea# only those planes are circular which are perpendicular to the main axis; all other planes going through the centre are elliptical; the largest of these are the meridian planes, in which is situated the main axis. Commonly all meridian planes are equal, as no transverse axes (or cross axes) are differentiated.

In my Monograph (1862) only very few forms of #Prunoidea#, such as _Didymocyrtis_ and _Spongurus_, are described, and the greater part of them are distributed under different genera of #Sphæroidea#, such as _Haliomma_ and _Actinomma_. In my Prodromus (1881) I separated them as the family Zygartida (p. 462). But it seems now much more convenient to restrict this term to a particular family and to give a wider extension to the whole suborder under the name #Prunoidea# (called after the characteristic ellipsoidal form of a plum, or _Prunus_, with its stone).

The suborder #Prunoidea# comprises seven different families, of which the Ellipsida constitutes the simplest and the probable common ancestral group. In all Ellipsida the fenestrated shell is simple, and never composed of concentric or twin shells. In their primitive genus _Cenellipsis_, the whole shell is geometrically nothing more than a simple ellipsoid (Pl. 39, figs. 1, 2). By development of radial spines it passes into _Ellipsidium_, by development of spongy framework into _Spongellipsis_. In the greater part of this family large spines are developed on both poles of the main axis of the shell, but sometimes instead of these solid spines, two opposite hollow fenestrated tubes are developed (_Pipettella_, Pl. 39, fig. 6).

The second family of #Prunoidea#, the Druppulida, is much richer in different forms than the simple Ellipsida. In this case the ellipsoidal shell is composed of two or three (rarely more) concentric shells. Constantly one or two of these fenestrated shells are enclosed in the central capsule, and may therefore be called "medullary shells"; and one or two (rarely more) lie outside the central capsule, "cortical shells." The inner medullary shells (one or two) are either spherical or ellipsoidal; the outer cortical shells (one or two, rarely more) are always ellipsoidal. All concentric shells are connected by radial beams. In the simplest form of the subfamily, _Druppula_ (Pl. 39, fig. 3), one medullary shell is connected with one cortical shell. By duplication of the medullary shell arises _Prunulum_ (Pl. 39, fig. 4), and by duplication or multiplication of the cortical shell _Cromyodruppa_ (Pl. 15, figs. 1-4) is formed. In by far the greater portion of this subfamily large spines are developed on both poles of the main axis of the cortical shell (Pls. 16, 17), but sometimes also instead of these solid spines two opposite hollow fenestrated tubes are developed (_Pipetta_, Pl. 39, figs. 7, 8).

{286}A third family of #Prunoidea#, closely allied to the two preceding families, is the Spongurida, in which we include all #Prunoidea# with an ellipsoidal or cylindrical, unjointed shell, in which the lattice-work of the cortical shell is transformed into an irregular, siliceous framework. In the simplest form, _Spongellipsis_, the simple lattice-shell of _Cenellipsis_ is substituted by an external spongy envelope. In other cases (_Spongurus_ and allied genera) the whole cavity of this external spongy shell is distended with a fine spongy framework. The subfamily of Spongodruppida is distinguished by the possession of a simple or double latticed medullary shell; this lies in the midst of the central capsule, and is connected by radial beams (perforating its membrane) with the enveloping spongy cortical shell. The surface of the latter may bear either radial spines, or two opposite strong polar spines, at the poles of the main axis (Pl. 17, fig. 12).

Closely allied to the Ellipsida and Druppulida are two other families of the #Prunoidea#, the Artiscida and Cyphinida, which differ from the former by a circular constriction in the equatorial plane of the ellipsoidal shell; and in this way assume a characteristic twin form, like a figure of eight. In the Artiscida the shell is simple (as in the Ellipsida), whereas in the Cyphinida it is composed of two or more concentric shells (as in the Druppulida). The simplest form of the Artiscida is _Artiscus_ (Pl. 39, fig. 9), differing from _Cenellipsis_ in the ring-shaped, equatorial constriction. In other Artiscida polar appendages are developed on both poles of the main axis, either in the form of solid, strong spines (_Stylartus_), or hollow fenestrated tubes (_Cannartus_, Pl. 39, fig. 10).

The family Cyphinida differs from the Druppulida in the equatorial constriction of the shell, and from the Artiscida in the presence of two or more concentric shells. One or two of these concentric fenestrated shells are enclosed in the central capsule (and therefore may be called "medullary shells"); the others (one or two, rarely more) lie outside of the central capsule (therefore "cortical shells"). The internal "medullary shells" are always spherical or somewhat lenticular, compressed from both sides; the external "cortical shells" have constantly a ring-like constriction in the equatorial plane, and "twin-shells" are therefore like a figure of eight. The simplest form of this subfamily is _Cyphanta_, composed of a simple medullary shell and a simple cortical shell, the two being connected in the equatorial plane by radial beams. In Cyphonium (Pl. 39, fig. 12) the medullary shell is doubled, and in _Cypassis_ (Pl. 39, fig. 13) the cortical shell likewise. On both poles of the main axis strong spines are often developed (_Cyphinus_, Pl. 39, fig. 14), or hollow fenestrated tubes (_Cannartidium_, Pl. 39, figs. 16-19).

The equatorial constriction of the ellipsoidal shell, which characterises the Artiscida and Cyphinida, is repeated or multiplied in the two following families, in the Panartida and Zygartida; in the former we find three ring-like strictures, in the latter five or more (lying in parallel transverse planes); therefore the fenestrated shell is composed in the one instance of four chambers, in the other of six or {287}more; all the chambers form a single series and have a common main axis. All constrictions lie in planes parallel to the equatorial plane of the original ellipsoid; in the centre of the latter constantly lies a double "medullary shell," composed of two concentric, either spherical or lenticular, compressed shells. In all Panartida we call the two inner chambers (on both sides of the equatorial constriction) "proximal chambers," the two outer chambers (on the poles of the main axis) "distal chambers." The four-chambered cortical shell of the Panartida is either simple (in _Panartus_, Pl. 40, figs. 1-4) or double, with an external mantle (as in _Peripanartus_, Pl. 40, figs. 5-7). The simplest form of the subfamily is _Panartus_ (_loc. cit._). In this case also on both poles of the main axis may be developed solid spines, or hollow fenestrated tubes (_Panarium_, Pl. 40, fig. 9).

The seventh and last family of the #Prunoidea#, the Zygartida is most nearly allied to the Panartida, and appears as a further developmental step from that family. Whilst in the Panartida the cortical shell is constantly four-chambered, with three parallel ring-like constrictions, in the Zygartida it is always prolonged and composed of six or more chambers, separated by five or more ring-shaped constrictions, in the middle of which is the equatorial stricture. In the centre of the latter (as also in the Panartida) always lies the double medullary shell, composed of two concentric, spherical, or lenticular shells. The number of the chambers of the cortical shells is commonly six or eight (with five to seven ring strictures), but it often mounts to ten and sometimes to twenty (with nineteen strictures), as in some species of _Zygartus_ (Pl. 40, fig. 13). All the chambers lie in one series, one behind another, with a common main axis. The cortical shell is usually simple (in _Ommatocampe_, Pl. 40, fig. 10), sometimes double (in _Desmocampe_, Pl. 40, fig. 12), rarely triple (in ZYGOCAMPE, Pl. 40, fig. 13). In all three cases hollow fenestrated tubes may be developed on the poles of the main axis.

The morphological references and the phylogenetic affinities of all #Prunoidea# are so complex, that they seem to represent a quite natural group; all forms of it may be derived from the common ancestral form _Cenellipsis_. But a far more difficult question is the manner in which its pedigree may be constructed. The oldest family is probably the simplest, namely, Ellipsida. From this the Druppulida may be derived by production of medullary shells, the Artiscida by equatorial constriction. The Cyphinida can be produced either from the Druppulida by equatorial constriction or from the Artiscida by development of medullary shells. The Panartida appear as further developmental steps of the Cyphinida, by duplication of the chamber number; and the Zygartida as further productions of the Panartida, by increasing the number of the chambers.

The seven subfamilies of the #Prunoidea# can be arranged in two sections according to the presence or absence of medullary shells. The Ellipsida, Spongellipsida, and Artiscida possess a simple cortical shell, without a medullary shell; they represent the {288}section Cenoprunida. All other families possess medullary shells, and so represent the section Coccoprunida.

Another character, which can be employed in the arrangement of the seven subfamilies in some larger groups, is the presence or absence of ring-like constrictions, by which the cortical shell is divided into chambers. I. The Monoprunida comprise all forms without any constriction, of which the Ellipsida are without a medullary shell, the Druppulida with one or two medullary shells, and the Spongurida with a spongy cortical shell. II. The Dyoprunida contain all forms with a cortical twin shell, or with two chambers separated by one equatorial constriction, of which the Artiscida are without a medullary shell and the Cyphinida have one or two medullary shells. III. The Polyprunida comprise all forms with several (three or more) constrictions, which separate four or more chambers, of which the Panartida have three constrictions and four chambers, and the Zygartida five or more constrictions and six or more chambers.

_The Central Capsule_ of the #Prunoidea# is originally ellipsoidal (monaxial), and preserves this form in the greater part of the genera. In some groups, where the axis of the ellipsoid is much prolonged, it passes over to the cylindrical form (with hemispherical vaultings on both poles), as in _Spongurus_ and _Spongocore_, in many Panartida and Zygartida. Very often the ellipsoidal or cylindrical capsule gets annular transverse constrictions, corresponding to those of the enveloping cortical shell (one single, equatorial stricture in the Artiscida and Cyphinida, three strictures in the Panartida, five or more in the Zygartida). In the Cenoprunida (Ellipsida and Artiscida, also in _Spongellipsis_) the central capsule lies freely in the cavity of the cortical shell, separated from its inner surface by the jelly-envelope; in all other groups it contains a part of the skeleton, the medullary shell and the beams which connect it with the enveloping cortical shell.

_Synopsis of the Families of_ #Prunoidea#.

{a. Shell simple, latticed (not
{ spongy), without enclosed internal
{ enclosed internal shells, 1. ELLIPSIDA.
A. MONOPRUNIDA. {
{b. Shell composed of two or more
Shell without { concentric latticed shells
transverse stricture { (not spongy), 2. DRUPPULIDA.
{
{c. Shell partially or wholly
{ composed of an irregular spongy
{ framework, 3. SPONGURIDA.

B. DYOPRUNIDA. {
{d. Shell simple, without enclosed
Shell bilocular, { internal shells, 4. ARTISCIDA.
divided by an {
equatorial stricture {
into two communicating{e. Shell composed of two or more
hemi-ellipsoidal { concentric shells, 5. CYPHINIDA.
shells. {

C. POLYPRUNIDA. {f. Shell with three parallel
{ strictures and therefore four
Shell multilocular, { cameræ, 6. PANARTIDA.
divided by three {
or more parallel {g. Shell with five or more parallel
transverse strictures { strictures and therefore six
into four or more { or more cameræ, 7. ZYGARTIDA.
serial cameræ. {

{289}Family XI. #ELLIPSIDA#, Haeckel, 1882 (Pls. 13, 14, 39).

_Definition._--#Prunoidea# with simple ellipsoidal shell, without equatorial stricture (without enclosed medullary shell); network a simple lattice lamella, not spongy. Central capsule ellipsoidal or cylindrical, without annular equatorial constriction.

The family #Ellipsida# comprises the simplest forms of #Prunoidea#, and probably represents the ancestral forms of this whole suborder. The fenestrated shell, which encloses the ellipsoidal central capsule, is a perfectly simple "cortical shell" of the same form, without enclosed "medullary shell." Its form is commonly a regular monaxial ellipsoid; sometimes a little modified by unequal growth of the two poles of the main axis. Two opposite large spines are often developed at these poles, or it may be that instead of these, two hollow fenestrated tubes are present.

The ellipsoidal fenestrated shell exhibits in the regular Ellipsida all the characters of a geometric ellipsoid; one main axis surpasses in length all other possible axes. All sections going through this main axis are "meridian sections," with elliptical periphery; all sections perpendicular to the main axis are "transverse sections," with circular periphery. The largest of these is the equatorial section, which divides the main axis into halves. The diameter of this equatorial plane is the "minor axis" of the ellipsoid.

The proportion of the two axes of the ellipsoidal shell, of the major vertical or main axis and the minor horizontal or equatorial axis, is commonly between 6 : 5 and 3 : 2. In the former case it approaches the spherical shell, from which it is derived; in the latter case it becomes almost fusiform or cylindrical. The network of silex, constituting the shell, is constantly a simple latticed lamella, never composed of concentric shells (as in Druppulida) or spongy (as in Spongurida). The network is often very regular and elegant, in other cases irregular.

The simplest genus among the Ellipsida, and probably the common ancestral form of the whole subfamily, is the genus _Cenellipsis_, possessing a simple ellipsoidal shell without any appendages. It is derived from _Cenosphæra_ (the simplest spherical shell) by the prolongation of one axis. _Cenellipsis_ passes over into _Ellipsidium_ by the production of radial spines on the surface (corresponding to _Heliosphæra_). _Axellipsis_ is a peculiar genus differing from _Cenellipsis_ in an axial rod, which corresponds to the minor or equatorial axis. In all other genera of the subfamily both poles of the main axis are distinguished by peculiar polar prolongations, either hollow fenestrated tubes (as in _Pipettella_) or strong solid spines. Both polar spines are of equal size and similar form in _Ellipsoxiphus_, unequal in _Ellipsostylus_. From the latter is derived _Lithapium_, by reduction and loss of one spine (so that only one remains); _Lithomespilus_, by production of a bunch of several spines at one pole. In the three latter genera both poles of the main axis are unequal, in all others equal.

{290}The central capsule of the Ellipsida is in all cases ellipsoidal, and occupies the largest part of the shell, being separated from its inner surface by a thinner or thicker jelly-mantle.

_Synopsis of the Genera of Ellipsida._

-------------------------------------------------------------------------
Ellipsoidal shell without polar appendages (neither solid spines nor
hollow tubes at the poles of the axis).
-------------------------------------------------------------------------
Surface without {Shell cavity
radial spines. { simple, without
{ an axial rod, 122. _Cenellipsis_.
{
{Shell cavity
{ with a transverse
{ axial rod, 123. _Axellipsis_.

Surface covered with radial spines, 124. _Ellipsidium_.
-------------------------------------------------------------------------
Ellipsoidal shell with polar appendages (either solid spines or hollow
fenestrated tubes) at the poles of the main axis.
-------------------------------------------------------------------------
Solid spines of {Shell cavity
similar shape, { simple, without
at both poles of { axial rods, 125. _Ellipsoxiphus_.
the main axis. {
{Shell cavity
{ with a cross of
{ axial rods, 126. _Axoprunum_.

Solid spines of {Two polar spines
different shape, { of different
at both poles { shape, 127. _Ellipsostylus_.
of the main {
axis. {A bunch of spines
{ at one pole
{ only, 128. _Lithomespilus_
{
{Only a single
{ spine at one
{ one pole, 129. _Lithapium_.

Two hollow fenestrated tubes opposite,
at the poles of the main axis, 130. _Pipettella_.

Genus 122. _Cenellipsis_,[161] n. gen.

_Definition_.--#Ellipsida# with simple ellipsoidal shell, without radial spines and without polar tubes.

The genus _Cenellipsis_ is the simplest and most primitive form, not only among the Ellipsida, but also among the #Prunoidea#, and it may therefore be regarded as the common ancestral form of the whole family. It corresponds to _Cenosphæra_ among the #Sphæroidea#, to _Cenodiscus_ among the #Discoidea#, to _Cenolarcus_ among the #Larcoidea#. Probably it is derived from _Cenosphæra_ by prolongation of one axis.

Subgenus 1. _Cenellipsium_, Haeckel.

_Definition._--Network of the shell regular, with meshes of equal size and similar form.

{291}1. _Cenellipsis primitiva_, n. sp.

Proportion of the longer axis of the ellipsoid to the shorter = 3 : 2. Network of the thin wall very delicate and regular, with hexagonal pores. All pores of nearly the same size and form, ten to twelve times as broad as the bars; nine to twelve on the half equator of the shell. Surface smooth.

_Dimensions._--Longer axis of the ellipsoid 0.09 to 0.11, shorter axis 0.06 to 0.08; pores 0.01, bars between them 0.001.

_Habitat._--Pacific, central area, Station 272, surface.

2. _Cenellipsis faceta_, n. sp. (Pl. 39, fig. 1).

Proportion of the longer axis of the ellipsoid to the shorter = 4 : 3. Network of the thin wall delicate and regular. All the pores of the same size and form, circular, with a hexagonal frame, twice to three times as broad as the bars; eight to ten on the half equator. Surface smooth or slightly spiny.

_Dimensions._--Longer axis of the ellipsoid 0.12 to 0.13, shorter axis 0.09 to 0.1; pores 0.013, bars 0.005.

_Habitat._--Pacific, central area. Station 274, surface.

3. _Cenellipsis ehrenbergii_, Haeckel.

_Haliomma (?) cenosphæra_, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 74, Taf xxvi. fig. 5.