Chapter XI: Literature and History (18)

_Dimensions._--Main axis of the shell 0.25, greatest breadth (in the equator of the proximal chambers) 0.15; equatorial stricture of the external shell 0.10, of the internal 0.07; pores of the internal shell of the proximal chambers 0.013, of the external 0.006; bars 0.003.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

3. _Peripanartus amphiconus_, n. sp. (Pl. 40, fig. 5).

Inner cortical shell with four very unequal chambers; both proximal chambers kidney-shaped (with regular, circular, hexagonally framed pores, twice as broad as the bars); both distal chambers conical, with a circle of large square pores at the base, the other pores very small, roundish. Outer cortical shell very thin, quite smooth, with irregular, roundish pores, envelops in younger specimens only the distal chambers. But the radial spines on the surface of the internal cortical shell of the proximal chambers indicate that these will also be afterwards enclosed by the growing of the external shell. This species exhibits the progressive (ontogenetic as well as phylogenetic) development of _Panartus amphiconus_.

_Dimensions._--Main axis of the outer cortical shell 0.3, its greatest breadth (at the prominent distal ends of the radial rods between the large square pores) 0.15; pores 0.003 to 0.001, bars 0.005; main axis of the inner cortical shell 0.26, its greatest breadth 0.13; pores of its distal chambers 0.003, of its proximal chambers 0.01; large square pores 0.03; bars 0.004.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

{384}Subgenus 2. _Peripanartium_, Haeckel.

_Definition._--Surface of the outer cortical shell covered with spines or thorns.

4. _Peripanartus atractus_, n. sp. (Pl. 40, fig. 7).

Inner cortical shell with four very unequal chambers; both proximal chambers spheroidal (with subregular, roundish pores, twice to three times as broad as the bars), both distal chambers nearly conical, with a circle of eight to ten very large square pores at the base; the other pores very small, roundish. Outer cortical shell envelops only the proximal chambers and the basal half of the distal chambers, appearing as the direct continuation of the microporous covering of their apical half. The whole external cortical shell is inflated in the equatorial zone, and hence assumes an irregular, spindle-like appearance. Its whole surface is rough with innumerable very short thorns.

_Dimensions._--Main axis 0.28, equatorial axis 0.17; pores of the external cortical shell 0.002 to 0.004, bars 0.002; main axis of the proximal chambers of the internal cortical shell 0.07, equatorial axis 0.09; pores 0.007, bars 0.004.

_Habitat._--North Pacific, Station 244, depth 2900 fathoms.

5. _Peripanartus cylindrus_, n. sp. (Pl. 40, fig. 6).

Internal cortical shell with four unequal chambers; both proximal chambers kidney-shaped (with regular, circular, hexagonally framed pores of the same breadth as the bars), both distal chambers nearly hemispherical, with a circle of eight to ten very large square pores at their base; the other pores very small, roundish. External cortical shell envelops the whole internal like a perfect hollow cylinder, which is closed at both poles by a hemispherical cap. The whole surface of this cylindrical mantle is perforated by innumerable very small roundish pores, and covered with small bristle-like spines.

_Dimensions._--Main axis of the cylinder 0.3, equatorial axis 0.12; pores and bars 0.006; spines of its surface 0.012 to 0.15; main axis of the internal cortical shell 0.2; equatorial axis (in the constriction) 0.06; pores and bars of its proximal chambers 0.007, of its distal chambers 0.003; large square pores at their base 0.02.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

Genus 165. _Panicium_,[204] n. gen.

_Definition._--#Panartida# with simple cortical shell and double medullary shell, with two opposite apical spines on both poles of the main axis, or with a group of polar spines.

The genus _Panicium_ comprises those forms of _Panartus_ which develop a peculiar armature on both poles of the cortical shell. This may be only a single strong spine {385}on each pole, lying in the main axis (subgenus _Panicidium_); or a bunch or a circle of polar spines diverging radially (subgenus _Panartidium_); in the latter case the polar spines can either form a bunch on the pole itself, or a crown of thorns around it.

Subgenus 1. _Panicidium_, Haeckel.

_Definition._--On both poles of the main axis only a single large spine.

1. _Panicium amphacanthum_, n. sp.

All four chambers of the cortical shell nearly of the same size and form, kidney-shaped, with subregular, circular pores, twice as broad as the bars; five to six pores on the half meridian, ten to eleven on the half equator of each chamber. Surface covered with small spines. On both poles of the main axis is a very strong, conical, apical spine, half as long as the main axis, on the base one-fourth as broad as the equatorial axis.

_Dimensions._--Main axis (without polar spines) 0.22, equatorial axis 0.06; pores 0.01, bars 0.005; length of the polar spines 0.12, basal thickness 0.015.

_Habitat._--Antarctic, Station 152, depth 1260 fathoms.

2. _Panicium amphistylus_, n. sp.

Both proximal chambers kidney-shaped, both distal chambers nearly hemispherical, somewhat smaller. Pores irregular, roundish, twice to three times as broad as the bars; four to six on the half meridian, eight to ten on the half equator of each chamber; a circle of larger square pores on the base of each distal chamber. Surface thorny. On both poles of the main axis one strong, pyramidal, apical spine, one-third as long as the main axis, on the base one-fourth as broad as the equatorial constriction. (Similar to _Panarium tubularium_, Pl. 40, fig. 9, but without tubes.)

_Dimensions._--Main axis (without polar spines) 0.2, equatorial axis 0.05; pores 0.005 to 0.01, bars 0.003; length of the polar spines 0.07, basal thickness 0.012.

_Habitat._--Antarctic, Station 156, depth 1975 fathoms.

Subgenus 2. _Panartidium_, Haeckel.

_Definition._--On both poles of the main axis a bunch or a circle of aggregated spines.

3. _Panicium scoparium_, n. sp.

Both proximal chambers kidney-shaped, both distal chambers nearly hemispherical, somewhat smaller. Pores irregular, polygonal, twice to five times as broad as the bars; six to eight on the half meridian, twelve to fourteen on the half equator of each chamber. Surface spiny, covered with thin, {386}bristle-like spines. On both poles of the main axis a bunch of six to eight aggregated larger conical spines, about as high as a single chamber.

_Dimensions._--Main axis (without polar spines) 0.2, equatorial axis 0.06; pores 0.005 to 0.015, bars 0.003; length of the polar spines 0.05, basal thickness 0.005.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

4. _Panicium coronatum_, n. sp. (Pl. 40, fig. 4).

Both proximal chambers kidney-shaped, covered with short stout spines. Pores irregular, roundish, twice to four times as broad as the bars; seven to eight on the half meridian, eleven to thirteen on the half equator of each chamber. Both distal chambers cap-like, separated from the former by a circle of ten to twelve very large square pores; the other pores very small, roundish. The circumpolar area is smooth, surrounded by a circle of ten to twelve very stout, conical, radial spines, which arise from the distal ends of the bars separating the large square meshes.

_Dimensions._--Main axis (without spines) 0.22, equatorial axis 0.08; greatest breadth in the equator of the chambers 0.1; pores of the proximal chambers 0.007 to 0.015, bars 0.004; square pores of the distal chambers 0.02 to 0.03, small pores 0.005, bars 0.004; length of the radial spines of the polar circles 0.07, basal thickness 0.007.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

Genus 166. _Peripanicium_,[205] n. gen.

_Definition._--#Panartida# with double cortical shell and double medullary shell, on both poles of the main axis with two opposite apical spines, or with a bunch or circle of polar spines.

The genus _Peripanicium_ differs from _Panicium_ only in the development of an outer reticulated envelope, which mantle-like surrounds the shell, and represents a second or external cortical shell. As in _Panicium_, its ancestral form, so also in _Peripanicium_, there can be distinguished two subgenera:--_Peripanicea_, where only a single large spine arises from each pole (lying in the main axis), and _Peripanicula_, where a variable number of spines is to be found, either diverging bunch-like from the pole itself, or surrounding it as a crown-like polar circle.

Subgenus 1. _Peripanicea_, Haeckel.

_Definition._--On both poles of the main axis only a single large spine.

1. _Peripanicium amphixiphus_, n. sp.

Internal cortical shell with four unequal chambers, with thorny surface. Both proximal chambers kidney-shaped (with subregular hexagonal pores, three times as broad as the bars). {387}Both distal chambers nearly hemispherical (with a circle of ten to twelve very large square pores at their base, the other pores very small). From both poles arises a single, strong, conical spine, half as long as the main axis. The internal cortical shell is very much like that of _Panarium tubularium_ (Pl. 40, fig. 9), but differs by the solid polar spines (instead of the hollow tubules) and by the formation of an external, cylindrical, very thin, cortical shell, which envelops the whole internal, and is connected with it by numerous beams. The surface of the external shell is quite smooth, and perforated by innumerable very small roundish pores.

_Dimensions._--Main axis of the external cortical shell 0.25, of the internal 0.19; transverse axis of the former 0.13, of the latter 0.08; pores of the proximal chambers of the internal shell 0.01, bars 0.003; pores of external cortical shell 0.002, bars 0.001; length of both polar spines 0.12, basal thickness of them 0.02.

_Habitat._--South Atlantic, near Tristan da Cunha, Station 333, depth 2025 fathoms.

Subgenus 2. _Peripanicula_, Haeckel.

_Definition._--On both poles of the main axis a bunch or a circle of aggregated polar spines.

2. _Peripanicium amphicorona_, n. sp. (Pl. 40, fig. 8).

_Peripanartus amphicorona_, Haeckel, 1881, Prodromus et Atlas (pl. xl.
fig. 8).

Internal cortical shell with four very unequal chambers. Both proximal chambers kidney-shaped, with subregular, polygonal pores, three times as broad as the bars. Both distal chambers double cone-shaped; the proximal cone of these formed by a circle of ten to twelve radial beams, which separate the same number of large square meshes; the distal cone with five to six circles of very small roundish, irregular pores. The continuation of the thin porous lamella of this distal cone forms the external cortical shell, whose surface is a little rough with innumerable very small thorns. On both poles is a large circular opening (nearly as broad as the equatorial constriction of the inner shell), surrounded by a delicate crown of thorns. The spines of this crown equal the diameter of the polar opening; they are very thin and bristle-like, connected by a few bridges and diverge outwards.

_Dimensions._--Main axis (without the crowns of polar thorns) 0.26, greatest breadth (in the equator of the proximal chambers) 0.15; equatorial constriction of the external shell 0.12, of the internal 0.07; pores of the proximal chambers of the internal cortical shell 0.01, of the external 0.005, bars 0.003; diameter of the circular polar opening 0.05; length of the polar spines 0.05.

_Habitat._--Pacific, central area, Station 271, depth 2425 fathoms.

3. _Peripanicium coronarium_, n. sp.

Internal cortical shell with four unequal chambers. Both proximal chambers kidney-shaped, with irregular, roundish pores, twice to four times as broad as the bars. Both distal chambers cap-like, with a basal circle of ten to twelve large square meshes, the other pores very small. External {388}cortical shell very thin, with smooth surface, and very small, irregular, roundish pores; it envelops the whole internal shell at a constant distance, which equals the breadth of the square meshes. From the distal ends of the radial beams between the square meshes arise on every polar circle ten to twelve strong spines, as direct prolongations of those beams. These form two regular, polar crowns of thorns. The inner part of the thorns (between both shells) has only one-third to one-fourth the length of the outer free part. (This species represents a further development of _Panicium coronatum_, Pl. 40, fig. 4, by secondary formation of an external mantle, like that of _Peripanartus atractus_, Pl. 40, fig. 7.)

_Dimensions._--Main axis 0.27, greatest breadth 0.15; pores of the internal proximal chambers 0.008 to 0.016, bars 0.004; square meshes of the distal chambers 0.03; pores of the outer cortical shell 0.003; length of the spines of the polar circles 0.1 to 0.15.

_Habitat._--Pacific, central area, Station 274, depth 2750 fathoms.

Genus 167. _Panarium_,[206] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Panartida# with simple cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on the poles of the main axis.

The genus _Panarium_ differs from _Panartus_ by two hollow latticed tubes, which start from both poles of the main axis and lie in it. It repeats therefore in this family the same peculiar and remarkable formation, which we find in _Pipettella_ among the Ellipsida, in _Pipetta_ among the Druppulida, in _Cannartidium_ among the Cyphinida, in _Cannartus_ among the Artiscida, &c.

Subgenus 1. _Panarelium_, Haeckel.

_Definition._--Surface of the shell smooth, without spines or thorns.

1. _Panarium facettarium_, n. sp.

Surface of the cortical shell smooth. All the four chambers nearly of the same size and form, kidney-shaped, about twice as broad as long. Pores of these subregular, circular, with hexagonal frames, about as broad as the bars; nine to ten on the half meridian, twelve to fourteen on the half equator of each chamber. Polar tubuli nearly cylindrical, longer than half the main axis of the cortical shell, about one-fourth as broad as the equatorial constriction. Pores of the tubuli of the same shape as those of the chambers, but only half as large. (This species is like _Pipetta tuba_, Pl. 39, fig. 7, but distinguished by three parallel transverse constrictions.)

_Dimensions._--Total length of the shell (without tubuli) 0.26; breadth of each chamber 0.12; pores 0.01, bars 0.01; length of the tubuli 0.15, breadth of them 0.03.

_Habitat._--Pacific central area, Station 268, depth 2900 fathoms.

{389}2. _Panarium pipettarium_, n. sp.

Surface of the cortical shell smooth. Both proximal chambers nearly kidney-shaped; both distal chambers somewhat smaller, hemispherical. Pores of all four chambers subregular, circular, without hexagonal frames, twice as broad as the bars; six to seven pores on the half meridian, ten to eleven on the half equator of each chamber. Polar tubuli slender, conical, nearly half as long as the main axis of the shell, one-third as broad at the base as the equatorial constriction. Pores of the tubuli of the same shape as those of the chambers, but only half as large. (This species resembles somewhat _Cannartiscus amphiconiscus_, Pl. 39, fig. 19, but with double the number of chambers.)

_Dimensions._--Total length of the shell (without tubuli) 0.25, greatest breadth 0.1; pores 0.008, bars 0.004; length of the polar tubuli 0.11, basal breadth 0.03.

_Habitat._--Pacific, western tropical part, Station 225, depth 4475 fathoms.

Subgenus 2. _Panaromium_, Haeckel.

_Definition._--Surface of the shell spiny, covered with short thorns.

3. _Panarium annularium_, n. sp.

Surface of the cortical shell thorny, everywhere covered with small bristle-like spines. All four chambers nearly of the same size and form, kidney-shaped. Their pores subregular, circular, three to four times as broad as the bars; seven to eight on the half meridian, ten to eleven on the half equator of each chamber. Polar tubuli conical, nearly half as long as the main axis, half as broad at the base as the equatorial constriction. Pores of the tubuli like those of the chambers, but only half as broad.

_Dimensions._--Total length of the shell (without tubuli) 0.16; breadth of each chamber 0.07; pores 0.006 to 0.008, bars 0.002; length of the polar tubuli 0.07, basal breadth 0.03.

_Habitat._--Northern Pacific, Station 253, depth 3125 fathoms.

4. _Panarium artophorum_, n. sp.

Surface of the shell thorny, with scattered small spines. Both proximal chambers nearly kidney-shaped; both distal hemispherical, somewhat smaller. Pores of all chambers irregular, roundish, little broader than the bars; four to five on the half meridian, six to eight on the half equator of each chamber. Polar tubuli cylindrical, longer than the half main axis, only one-fourth as broad the equatorial constriction. Pores of the tubuli only one-third to one-fourth as broad as those of the chambers.

_Dimensions._--Total length of the shell (without tubuli) 0.22, greatest breadth (in the equator of the proximal chambers) 0.09; pores and bars 0.008 to 0.012; length of the polar tubuli 0.14, breadth of them 0.02.

_Habitat._--Southern Pacific, Station 289, depth 2550 fathoms.

{390}5. _Panarium tubularium_, n. sp. (Pl. 40, fig. 9).

Surface of the cortical shell thorny, covered with small spines. Both proximal chambers nearly kidney-shaped, with irregular, polygonal pores, three to four times as broad as the bars; five to six pores on the half meridian, nine to ten on the half equator of each chamber. Both distal chambers nearly hemispherical, with a circle of ten to twelve large square pores at their base; the other pores much smaller, irregular, roundish. Polar tubuli prismatic, with prominent edges, nearly half as long as the main axis, only one-fourth as broad as the equatorial constriction. Pores of the tubuli very small, in longitudinal series between the edges.

_Dimensions._--Total length of the shell (without tubuli) 0.18 to 0.2, greatest breadth (in the equator of the proximal chambers) 0.07 to 0.09; pores 0.003 to 0.01, bars 0.002 to 0.004; length of the polar tubuli 0.06 to 0.09, breadth of them 0.015 to 0.02.

_Habitat._--Pacific, central area, Stations 270 to 272, depth 2425 to 2925 fathoms.

Genus 168. _Peripanarium_,[207] n. gen.

_Definition._--#Panartida# with double cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on the poles of the main axis.

The genus _Peripanarium_ differs from _Panarium_ only in the development of an outer reticulated envelop, which mantle-like surrounds the shell and represents a second or external cortical shell. It bears therefore to _Panarium_ the same relation as _Peripanartus_ to _Panartus_, &c.

1. _Peripanarium cenoconicum_, n. sp.

Internal cortical shell with four kidney-shaped chambers of nearly the same form and size; their pores irregular, roundish, twice to four times as broad as the bars. External cortical shell cylindrical, hemispherical at both poles, with irregular, very small, roundish pores, only one-third to one-half as large as those of the internal. From both poles of the internal cortical shell arises a hollow conical fenestrated tube, which perforates the external. The outer free part of this slender cone equals in length the inner part or the distance between the two cortical shells, which is about equal to the length of one chamber. External surface covered with small thorns. (This species has the same appearance as _Desmartus larvalis_, Pl. 40, fig. 12, but has only four chambers instead of six.)

_Dimensions._--Main axis (without cones) 0.23, greatest breadth 0.11; pores of the inner cortical shell 0.004 to 0.009, of the outer 0.002 to 0.003; bars of the former 0.002, of the latter 0.001; total length of the polar cones 0.05, basal thickness of them 0.03.

_Habitat._--West Tropical Pacific, Station 225, depth 4475 fathoms.

{391}2. _Peripanarium cenocylindricum_, n. sp.

Internal cortical shell with four unequal chambers, the two proximal kidney-shaped, the two distal conical, and somewhat smaller; pores irregular, polygonal-roundish, twice to five times as broad as the bars. External cortical shell nearly spindle-shaped, in the equatorial zone inflated, conical, tapering towards both poles, its pores very small, roundish, its surface covered with small thorns. The shell of this species resembles very much _Peripanartus atractus_ (Pl. 40, fig. 7), but differs by the hollow cylindrical polar tubes, which arise from both poles of the inner cortical shell and attain more than half the length of the main axis. They are open at their ends (broken away), about as broad as the outer medullary shell, and perforated by irregular, roundish pores.

_Dimensions._--Main axis (without polar tubes) 0.28, greatest breadth (in the equator) 0.16; pores of the inner cortical shell 0.004 to 0.01, of the outer 0.002 to 0.005; bars of the former 0.004, of the latter 0.002; total length of the polar tubes 0.16, breadth of them 0.03.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

Family XVII. #ZYGARTIDA#, Haeckel (Pl. 40, figs. 10-13).

_Zygartida_, Haeckel, 1881, Prodromus, p.462 (_sensu restricto_).

_Definition._--#Prunoidea# with annulated cortical shell, the external shell being divided by five or more parallel transverse constrictions into six or more chambers, enclosing in the centre two internal concentric shells (medullary shells). Central capsule cylindrical, commonly annulated (corresponding to the transverse annular constrictions of the cortical shell).

The family #Zygartida#, the seventh and last of the #Prunoidea#, comprises, in the sense here restricted, all those #Prunoidea# in which the cortical shell is annulated and composed of six to twenty or more (at least six) cameræ, lying one behind another in the elongated main axis, and separated by five or more annular constrictions. When I constituted this family in 1881 (_loc. cit._), I had given to it a much wider extent, embracing all those #Prunoidea# which exhibit annular constrictions of the cortical shell; as the number of these, in consequence of further researches, is much increased, it seems now more convenient to restrict the family to the extent here given.

No doubt the Zygartida must be derived from the Panartida by progressive growth of the cortical shell in the main axis and accompanying increase of the number of its chambers. Whilst this number in the Panartida is constantly restricted to four, in the Zygartida it amounts to ten, twenty, or more, and is in the lowest case six (Pl. 40, fig. 10). The maximum number is variable in the different species, but of course also different in the various degrees of individual development. Each Zygartid is at the beginning of its growth a Cyphinid, later a Panartid. The number of the annular constrictions separating the chambers and lying in parallel transverse planes is at least {392}five, but may amount to nineteen, to twenty-one or more; they lie constantly in pairs on both sides of the equatorial constriction (Pl. 40, figs. 12, 13).

The cortical shell may either remain simple (_Ommatocampe_, Pl. 40, fig. 10), or become double (_Desmocampe_, Pl. 40, fig. 12), or sometimes triple (_Zygocampe_, Pl. 40, fig. 13). In the latter cases the outer (secondary and tertiary) cortical shells are commonly incomplete, and only developed around the proximal chambers of the complete first (primary) cortical shell, its distal chambers remaining simple.

_The Medullary Shell_ is constantly double, as in the Panartida; its form is either spherical or lenticular, compressed in the direction of the main axis. It is always connected with the equatorial constriction of the cortical shell by a number of radial beams, lying either in the equatorial plane or on each side of it (Pl. 40, figs. 10-13).

_The Central Capsule_ of the Zygartida is constantly cylindrical; its increasing growth on both poles of the axis corresponds to that of the including cortical shell. Commonly (but not always) its cylindrical surface is annulated, with five or more transverse strictures, corresponding to those of the cortical shell. From the inner surface of the latter it is separated by a jelly-mantle, the calymma.

_Synopsis of the Genera of Zygartida._

I. Ommacampida. { Without polar tubes, 169. _Ommatocampe_.
1. Cortical shell {
simple. { With two hollow fenestrated
(Medullary shell { tubes, on the poles of
double.) { the axis, 170. _Ommatartus_.

II. Desmocampida. { Without polar tubes, 171. _Desmocampe_.
2. Cortical shell {
double. { With two hollow fenestrated
(Medullary shell { tubes, on the poles of
double.) { the axis, 172. _Desmartus_.

III. Zygocampida. { Without polar tubes, 173. _Zygocampe_.
3. Cortical shell {
triple. { With two hollow fenestrated
(Medullary shell { tubes, on the poles of
double.) { the axis, 174. _Zygartus_.

Genus 169. _Ommatocampe_,[208] Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 832.

_Definition._--#Zygartida# with simple cortical shell and double medullary shell, without polar tubes.

The genus _Ommatocampe_ was founded by Ehrenberg in 1860 for one of his "_Haliommatina_," with the following diagnosis:--"Shell rod-like, long, articulate, with nucleus, without spines, with four or more joints." The species figured by him, _Ommatocampe {393}polyarthra_, exhibits five pairs of chambers on both sides of the meridian plane of the cortical shell, the centre of which includes a double medullary shell. It represents the most simple form of all Zygartida, and may be derived phylogenetically from _Cyphonium_ simply by multiplication of the chambers of the cortical shell, growing on both poles of the main axis.

Subgenus 1. _Ommatocampium_.

_Definition._--Surface of the cortical shell smooth or rough, without thorns or spines, also without polar spines.

1. _Ommatocampe polyarthra_, Ehrenberg.

_Ommatocampe polyarthra_, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss.
Berlin, p. 279, Taf. vi. fig. 9.

Cortical shell with smooth surface, composed of six to ten chambers of the same size and form. Every chamber kidney-shaped, about twice as broad as long, with three transverse rows of circular, subregular pores, twice to three times as broad as the bars. Both medullary shells spherical.

_Dimensions._--Length of the six-chambered cortical shell 0.15; greatest breadth of each chamber 0.04; pores 0.005 to 0.007, bars 0.002 to 0.003.

_Habitat._--Californian Sea, depth 2600 fathoms, Ehrenberg; Pacific, central area, Station 268, depth 2900 fathoms; fossil in the Tertiary rocks of Barbados, Haeckel.

2. _Ommatocampe increscens_, Stöhr.

_Ommatocampe increscens_, Stöhr, 1880, Palæontogr., vol. xxvi. p. 90,
Taf. ii. fig. 2, _a_, _b_.

Cortical shell with rough surface, composed of six to ten chambers of nearly the same size and form; the breadth of the chambers a little increasing towards both poles. Every chamber kidney-shaped, the proximal chambers twice as broad as long, with four or five transverse rows of pores; the distal chambers three to four times as broad as long, with two or three transverse rows of pores. Form of the pores irregular, roundish, bars between them in the distal part smaller, in the proximal part larger than the pores. Both medullary shells compressed lenticular.

_Dimensions._--Length of the six-chambered cortical shell 0.22; greatest breadth of the chambers 0.09 to 0.1; pores and bars 0.003 to 0.006.

_Habitat._--Fossil in the Tertiary rocks of Sicily, Grotte, Stöhr.

3. _Ommatocampe annulata_, n. sp.

Cortical shell with smooth surface, composed of six to twelve chambers of nearly the same size and form. Each chamber kidney-shaped, twice as broad as long, with four to five transverse rows of {394}irregular, roundish pores, once to five times as broad as the bars. On the base of each distal chamber (beginning in the second or third pair) a circle of twelve to sixteen larger square pores. Both medullary shells compressed lenticular. (Resembles the inner cortical shell of _Desmartus larvalis_, Pl. 40, fig. 12, but is without the polar tubes and the outer envelope of this species.)

_Dimensions._--Length of the six-chambered cortical shell 0.23; greatest breadth of each chamber 0.07; pores 0.002 to 0.01, bars 0.002.

_Habitat._--Cosmopolitan; Mediterranean, Atlantic, Pacific, in various depths.

Subgenus 2. _Ommatocampula_, Haeckel.

_Definition._--Surface of the cortical shell thorny or spiny, but without peculiar polar spines and without regular coronals of spines.

4. _Ommatocampe erucæformis_, n. sp.

Cortical shell with spiny surface, composed of six to twelve chambers of nearly the same size and form, the distal chambers a little smaller. The form and structure of the cortical shell is nearly the same as in the foregoing species, only the pores are somewhat larger, and the whole surface is covered with bristle-like radial spines, about half as long as the breadth of one chamber. Both medullary shells compressed and lenticular.

_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest breadth of each chamber 0.08; pores 0.005 to 0.012, bars 0.002.

_Habitat._--North Atlantic, Canary Islands, Station 353, depth 2965 fathoms.

5. _Ommatocampe nereis_, n. sp. (Pl. 40, fig. 10).

Cortical shell with spiny surface, composed of six (or more) chambers of different size and structure. Both proximal chambers kidney-shaped, with subregular, circular, hexagonally framed pores, twice as broad as the bars. All following chambers cap-like, with much smaller, irregular, roundish pores, at the base of every chamber a circle of ten to twelve large square pores. Spines of the surface short, irregularly scattered. Both medullary shells spherical. (All the observed specimens possessed only six chambers.)

_Dimensions._--Length of the six-chambered cortical shell 0.25; greatest breadth of each chamber 0.08; pores of both proximal chambers 0.01, bars 0.005; basal pores of the other chambers 0.02; pores of their distal caps 0.003 to 0.006, bars 0.003.

_Habitat._--Pacific, central area, Stations 271 to 274, depth 2350 to 2750 fathoms.

Subgenus 3. _Ommatocorona_, Haeckel.

_Definition._--Surface of the cortical shell spiny, on every chamber a regular circle or coronal of radial spines.

{395}6. _Ommatocampe chætopodum_, n. sp.

Cortical shell with spiny surface, composed of six (or more) kidney-shaped chambers of different size and form. Both proximal chambers kidney-shaped, with subregular, circular, hexagonally framed pores, about as broad as the bars. All the following chambers hemispherical, with irregular, roundish pores; at the base of every chamber a circle of ten to twelve larger square pores. The beams between these latter are prolonged into free radial spines, twice as thick as the bars. Therefore every chamber is surrounded by a circle of radial spines, like those of _Panicium coronatum_ (Pl. 40, fig. 4). Both medullary shells lenticular.

_Dimensions._--Length of the six-chambered cortical shell 0.3, greatest breadth 0.08, pores and bars of both proximal chambers 0.01; pores of the other chambers 0.002 to 0.008; square pores 0.02, bars 0.005; length of the coronal spines 0.03, thickness 0.01.

_Habitat._--Indian Ocean, Madagascar, Rabbe.

Subgenus 4. _Ommatacantha_, Haeckel.

_Definition._--Surface of the shell smooth or spiny, on the poles of the main axis occur two strong opposite polar spines.

7. _Ommatocampe amphilonche_, n. sp.

Cortical shell composed of six kidney-shaped chambers of nearly the same size and structure; every chamber twice as broad as long, with four to five transverse rows of irregular, roundish pores, once to four times as broad as the bars. Both medullary shells lenticular. Surface of the cortical shell covered with bristle-like spines. On both poles of the main axis one larger, strong, conical spine, about half as long as this axis, and on the base as broad as the inner medullary shell. (Resembles on the whole _Desmartus larvalis_, Pl. 40, fig. 12, but without external mantle, and with two solid polar spines instead of the polar tubes.)

_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest breadth of each chamber 0.08; pores 0.002 to 0.08, bars 0.002; length of the polar spines 0.12, basal thickness 0.02.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

Genus 170. _Ommatartus_,[209] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Zygartida# with simple cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus _Ommatartus_ differs from _Ommatocampe_ by the development of two hollow fenestrated tubes on both poles of the main axis, and bears therefore the same relation to it as _Cannartidium_ to _Cyphonium_. The former two genera differ from the two latter by the augmentation of the chambers of the cortical shell.

{396}1. _Ommatartus amphicanna_, n. sp.

Cortical shell with spiny surface, composed of six chambers of equal size and kidney-shaped; every chamber with four to five transverse rows of irregular, roundish pores, twice to three times as broad as the bars. Both medullary shells lenticular. Polar tubes conical, about as long as one chamber, with smaller pores. Both medullary shells spheroidal, more or less compressed. (Resembles _Desmartus larvalis_, Pl. 40, fig. 12, but is without the external shell.)

_Dimensions._--Length of the six-chambered cortical shell 0.24; greatest breadth of each chamber 0.07; pores 0.008 to 0.012, bars 0.004; length of the polar tubes 0.04 to 0.05, basal thickness 0.02.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

2. _Ommatartus amphisiphon_, n. sp.

Cortical shell with spiny surface, composed of six or eight chambers of different size and form. Both proximal chambers kidney-shaped, each with five to six transverse rows of irregular, polygonal pores, three to four times as broad as the bars. The other (four to six) chambers somewhat smaller, more hemispherical, with smaller, irregular pores, but on the base of each a circle of ten to twelve larger square pores. Polar tubuli prismatic, about half as long as the main axis, with prominent edges and longitudinal rows of smaller pores between them. Both medullary shells lenticular. (Resembles closely _Panarium tubularium_, Pl. 40, fig. 9, but with six to eight chambers instead of four, and with longer tubuli.)

_Dimensions._--Length of the six-chambered cortical shell 0.26; greatest breadth of the proximal chambers 0.09, of the distal chambers 0.07; pores of the former 0.01, of the latter 0.004; large square pores 0.013, bars 0.003; length of the polar tubes 0.1 to 0.12, thickness 0.02.

_Habitat._--South Pacific, Station 297, depth 1775 fathoms.

3. _Ommatartus amphobolus_, n. sp.

Cortical shell with spiny surface, composed of six chambers of different size and form. Both proximal chambers kidney-shaped, with four to five transverse rows of subregular, circular pores, twice as broad as the bars. Both middle chambers cap-like, with a basal circle of ten to twelve larger square pores, and small roundish pores on the cap. Both distal chambers smaller, conical, with very small roundish pores. Polar tubuli conical, nearly half as long as the main axis, also with very small pores. Both medullary shells lenticular.

_Dimensions._--Length of the six-chambered shell 0.28, greatest breadth 0.08; pores of the proximal chambers 0.01, bars 0.005; pores of the distal chambers and the polar tubes 0.002 to 0.004, bars 0.002; length of the polar tubes 0.13, basal thickness 0.03.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

Genus 171. _Desmocampe_,[210] n. gen.

_Definition._--#Zygartida# with double cortical shell and double medullary shell, without polar tubes.

{397}The genus _Desmocampe_ differs from _Ommatocampe_ in the duplication of the jointed cortical shell; the radial spines, which start from the surface of the inner cortical shell, are connected one with another by transverse communicating branches which form an outer envelop around it; but this reticulated mantle is commonly not quite perfect and more or less irregular.

1. _Desmocampe catenula_, n. sp.

Inner cortical shell with six to eight chambers of the same size and form. Every chamber kidney-shaped, with three to four transverse rows of circular, subregular pores, twice as broad as the bars. Outer cortical shell cylindrical, hemispherical at both poles, with smooth surface and irregular, roundish pores of very different size. Distance between the two cortical shells equals the diameter of the outer medullary shell, which, like the inner, is spherical. (Resembles Ommatocampe polyarthra, Ehrenberg, 1872, _loc. cit._, Taf. vi, fig. 9, but differs in the external mantle.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.16, of the outer 0.21; greatest breadth of each chamber of the former 0.05, of the latter 0.09; pores of the inner 0.006, bars 0.003; pores of the outer 0.002 to 0.008, bars 0.002.

_Habitat._--North Pacific, Station 237, off Japan, surface.

2. _Desmocampe tænioides_, n. sp.

Inner cortical shell with six to ten chambers of nearly the same size and form; the distal chambers somewhat smaller. Every chamber kidney-shaped, with four to five transverse rows of irregular roundish pores, twice to three times as broad as the bars. Outer cortical shell cylindrical, hemispherical at both poles, with spiny surface; its pores like those of the inner, but the bars between them much thinner. Distance between the two cortical shells equals the diameter of the outer medullary shell. Both medullary shells lenticular. (Resembles _Desmartus larvalis_, Pl. 40, fig. 12, but is without polar tubes.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the outer 0.3; greatest breadth of the former 0.07, of the latter 0.11; pores 0.005 to 0.012; bars of the inner shell 0.004, of the outer 0.001.

_Habitat._--Pacific, central area, Station 268, depth 2900 fathoms.

3. _Desmocampe aphrodite_, n. sp.

Inner cortical shell with six to ten chambers of different size and structure. Both proximal chambers kidney-shaped, with five to six transverse rows of subregular, circular, hexagonally-framed pores, twice as broad as the bars. All following chambers cap-like, with much smaller, irregular, roundish pores, on the base of each a circle of ten to twelve large square pores. Outer cortical shell cylindrical, on both poles hemispherical, with spiny surface and very delicate network of small polygonal pores. Both medullary shells spherical. (The inner cortical shell of this species resembles that of _Ommatocampe nereis_, Pl. 40, fig. 10; the outer that of _Cyphocolpus virginis_, Pl. 40, fig. 11.)

{398}_Dimensions._--Length of the six-chambered internal cortical shell 0.25, of the outer 0.3; greatest breadth of the former 0.08, of the latter 0.12; pores of the proximal chambers of the inner shell 0.01, bars 0.005; pores of the distal chambers 0.003 to 0.005, square pores 0.02, bars 0.003; pores of the external cortical shell 0.002 to 0.006, bars 0.001.

_Habitat._--North Atlantic, Station 353, depth 2965 fathoms.

4. _Desmocampe atractus_, n. sp.

Inner cortical shell with six chambers of very different size and structure. Both proximal chambers kidney-shaped, with seven to eight transverse rows of subregular, roundish pores, twice to three times as broad as the bars. Both middle chambers cap-like, on the base with a circle of eight to ten very large square pores, on the distal cap with small irregular, roundish pores. Both distal chambers conical, also with small irregular, roundish pores. Outer cortical shell spindle-shaped, inflated in the equatorial zone, tapering conically towards both poles, with very delicate network of small roundish pores and thin bars. Surface covered with innumerable very small spines. Both medullary shells lenticular. (Resembles very much _Peripanartus atractus_, Pl. 40, fig. 7, but differs in the number of the chambers and their proportion to the outer mantle, which envelops spindle-like all six chambers.)

_Dimensions._--Length of the six-chambered internal cortical shell 0.27, of the outer 0.32; greatest breadth of the former 0.09, of the latter 0.15; pores of the inner cortical shell (on an average)--proximal chambers 0.008, middle chambers 0.02, distal chambers 0.004, bars 0.004; pores of the outer cortical shell 0.002 to 0.004, bars 0.002.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

Genus 172. _Desmartus_,[211] n. gen.

_Definition._--#Zygartida# with double cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus _Desmartus_ differs from _Desmocampe_ by the development of two hollow fenestrated tubes, opposite on both poles of the main axis, and bears therefore the same relation to it as _Ommatartus_ to _Ommatocampe_. Both the former genera can be produced from the two latter by duplication of the cortical shell.

1. _Desmartus larvalis_, n. sp. (Pl. 40, fig. 12).

_Zygartus larvalis_, Haeckel, 1881, Prodromus et Atlas (pl. xl, fig. 12).

Inner cortical shell composed of six kidney-shaped chambers of nearly the same size and structure; every chamber twice as broad as long, with four to five transverse rows of irregular, roundish pores, twice to five times as broad as the bars; the basal pores of the distal chambers {399}somewhat larger and more square. Outer cortical shell cylindrical, hemispherical at both poles, with irregular, polygonal pores, on an average twice as large as those of the inner, but the bars between them much thinner. Outer surface spiny. Both medullary shells lenticular. Polar tubes conical, a little longer than one internal chamber, as broad at the base as the inner medullary shell. Sometimes the tubes exhibit prominent edges (as in the lower spine of fig. 12); the pores of these are very small, and roundish.

_Dimensions._--Length of the six-chambered internal cortical shell 0.23, of the external 0.3; greatest breadth of the former 0.07, of the latter 0.11; pores of the inner shell 0.004 to 0.01, of the outer 0.01 to 0.02; bars of the former 0.002, of the latter 0.001; length of the polar tubes 0.05, basal thickness 0.02.

_Habitat._--North Pacific, Station 241, depth 2300 fathoms.

2. _Desmartus tubulatus_, n. sp.

Inner cortical shell composed of six to ten kidney-shaped chambers, tapering in size towards both poles, every chamber with six to seven transverse rows of irregular, roundish pores, twice to six times broader than the bars. Outer cortical shell spindle-shaped, in the equatorial zone inflated, tapering towards both poles, its network similar to the inner, only more delicate. Polar tubes conical, twice as long as an inner chamber, as broad at the base as the outer medullary shell. Both medullary shells lenticular.

_Dimensions._--Length of the six-chambered internal cortical shell 0.25, of the external 0.32; greatest breadth of the former 0.08, of the latter 0.12; pores of the inner shell 0.002 to 0.012, of the outer 0.003 to 0.01; bars of the former 0.002, of the latter 0.001; length of the polar tubes 0.07, basal thickness 0.03.

_Habitat._--North Pacific, Station 256, depth 2950 fathoms.

Genus 173. _Zygocampe_,[212] n. gen.

_Definition._--#Zygartida# with triple (or multiple) cortical shell and double medullary shell, without polar tubes.

The genus _Zygocampe_ differs from _Desmocampe_ and _Ommatocampe_ by the multiplication of the cortical shell, which is composed of three or more concentric envelopes. The three mentioned genera form therefore a phylogenetic series, produced by the concentric increase on the outside of the jointed cortical shell. Commonly the second cortical shell is not as complete as the first (or innermost), and the third (or outermost) is yet more incomplete. Rarely the number of the concentric cortical shells surpasses three.

1. _Zygocampe pupula_, n. sp.

Inner cortical shell with six to twelve chambers of nearly the same size and form. Every chamber kidney-shaped, with four to five transverse rows of circular, subregular pores, twice as {400}broad as the bars. Middle cortical shell cylindrical, hemispherical at both poles, with subregular circular pores somewhat smaller than those of the inner; the bars also thinner. Outer cortical shell of the same form as the middle, but with very delicate network, and quite irregular, roundish pores and very thin bars. Surface quite smooth. Both medullary shells lenticular. (May be regarded in a phylogenetic as well as an ontogenetic sense, as the further developmental form of _Desmocampe catenula_ and _Ommatocampe polyarthra_.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.17, of the middle 0.22, of the outer 0.27; greatest breadth of the first 0.05, of the second 0.09, of the third 0.12; pores of the inner cortical shell 0.005, of the middle 0.004, of the outer 0.003 to 0.012; bars of the first 0.003, of the second 0.002, of the third 0.001.

_Habitat._--Pacific, central area, Station 266, depth 2750 fathoms.

2. _Zygocampe corasium_, n. sp.

Inner cortical shell with six to eight chambers of different size and form. Both proximal chambers kidney-shaped, with five to six transverse rows of subregular, circular, hexagonally framed pores, twice as broad as the bars. All following chambers cap-like, the distal somewhat smaller; their pores much smaller, irregular, roundish; only at the base of each chamber a circle of ten to twelve large square pores. Middle cortical shell cylindrical, in the equatorial zone a little constricted, hemispherical at both poles, with irregular delicate network of roundish, polygonal meshes. Outer cortical shell of the same form as the middle, but with a very delicate and quite irregular network of polygonal meshes. Commonly this outer mantle is incomplete, and sometimes interwoven in a spongy manner with the middle (or also with the inner). Surface covered with many irregular, thin, bristle-like spines. Both medullary shells lenticular. (May be considered in a phylogenetic and ontogenetic sense as a further developmental stage of _Desmocampe aphrodite_ and _Ommatocampe nereis_, Pl. 40, fig. 10.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.24, of the middle 0.3, of the outer 0.36; greatest breadth of the first 0.08, of the second 0.12, of the third 0.16, pores of the first (on an average) 0.005 to 0.02, of the second 0.003 to 0.015, of the third 0.01 to 0.05; bars corresponding 0.005 or 0.003 or 0.001.

_Habitat._--North Pacific, Station 253, depth 3125 fathoms.

3. _Zygocampe chrysalidium_, n. sp. (Pl. 40, fig. 13).

Inner cortical shell with six to eighteen chambers of different size and form. Both proximal chambers kidney-shaped, with six to seven transverse rows of subregular, circular pores, three to four times as broad as the bars. All following chambers with more irregular pores, with a circle of ten to twelve larger square pores at the base. Middle cortical shell with smaller, irregular, roundish pores. Outer cortical shell with larger polygonal, quite irregular pores. Both outer shells appear commonly incomplete or somewhat irregularly developed, and sometimes in a spongy manner interwoven with one another. Surface covered with irregular, bristle-like spines. Both medullary shells spherical. The breadth of the chambers decreases gradually towards both poles, so that the whole shell assumes a spindle form. Sometimes on both poles is developed a short conical {401}polar tube (in fig. 13 only on the upper pole), and so this species is transformed into _Zygartus chrysalis_.

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of the second 0.11, of the third 0.14; pores (on an average) 0.01 (0.002 to 0.02), bars 0.002 to 0.005.

_Habitat._--Pacific, central area, Stations 272 to 274, depth 2350 to 2750 fathoms.

Genus 174. _Zygartus_,[213] Haeckel, 1881, Prodromus, p. 463.

_Definition._--#Zygartida# with triple (or multiple) cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on both poles of the main axis.

The genus _Zygartus_ differs from Zygocampe by the development of two hollow fenestrated tubes, on the two opposite poles of the main axis. It exhibits therefore to the latter the same relation that _Desmartus_ does to _Desmocampe_ and _Ommatartus_ to _Ommatocampe_; it differs from these by the multiplication of the cortical shell, which is composed of at least three concentric envelopes.

1. _Zygartus doliolum_, n. sp.

Inner cortical shell composed of six (or more) kidney-shaped chambers, all nearly of the same size and structure, every chamber with four to five transverse rows of irregular, roundish pores, twice to four times as broad as the bars; the basal pores scarcely larger than the apical pores. Middle cortical shell nearly of the same structure as the inner, only the pores larger and the bars thinner. Outer cortical shell cylindrical, hemispherical at both poles, its network very delicate, with large irregular, polygonal pores, and very thin bars between them; its surface covered with thin bristle-like spines. Both medullary shells lenticular. Polar tube cylindrical, with conical apex, and with very small pores; its length equals the breadth of two internal chambers, its breadth that of the inner medullary shell. (This species appears to be a further developed form of _Ommatocampe annulata_ and _Desmartus larvalis_, Pl. 40, fig. 12.)

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of the second 0.11, of the third 0.15; pores of the inner shell 0.005 to 0.01, of the middle 0.003 to 0.007, of the outer 0.008 to 0.02; bars of the first 0.002, of the second and third 0.001; length of the polar tubes 0.15, basal thickness 0.02.

_Habitat._--Pacific, central area, Station 270, depth 2925 fathoms.

2. _Zygartus chrysalis_, n. sp. (Pl. 40, fig. 13).

Inner cortical shell composed of six to twenty (commonly eight to twelve) chambers of different size and form. Both proximal chambers nearly hemispherical, with spiny surface and subregular, {402}circular pores, three to four times as broad as the bars. All following chambers cap-like, tapering towards both poles, with more irregular, roundish pores, with a circle of ten to twelve larger square pores at the base. Middle cortical shell with smaller roundish pores. Outer cortical shell with larger polygonal, quite irregular pores. Both medullary shells lenticular. Polar tubes conical or cylindrical with conical apex, of very variable length, sometimes not longer than one internal chamber, at other times twice to four times as long (in the figured specimen not fully developed, as also a part of the shells). Differs from _Zygocampe chrysalis_ only by the production of polar tubes.

_Dimensions._--Length of the six-chambered inner cortical shell 0.25, of the middle 0.3, of the outer 0.35; greatest breadth of the first 0.07, of the second 0.11, of the third 0.14; other measures the same as in _Zygocampe chrysalis_; length of the tubes 0.05 to 0.12 or more.

_Habitat._--Pacific, central area, Stations 270 to 274, depth 2350 to 2925 fathoms.

----

Suborder V. DISCOIDEA, Haeckel (Pls. 31-38, 41-48).

_Discida_ vel _Discoidea_, Haeckel, 1862, Monogr. d. Radiol., pp. 56,
476.
_Discoida_, _Discoidea_, _Discida_, Haeckel, 1878, Protistenreich, p.
103.

_Definition._--SPUMELLARIA with discoidal or lenticular central capsule (often with radial prolongations, rarely allomorphic); with discoidal or lenticular fenestrated siliceous shell (often with radial spines or fenestrated arms, rarely allomorphic). Growth reduced or diminished in the direction of one dimensive axis.

The section #Discoidea# comprises those SPUMELLARIA in which the fenestrated shell is more or less discoidal or lenticular, flattened or compressed in the direction of one axis. The geometric fundamental form of the latticed shell, which in the #Sphæroidea# is a sphere, here becomes a flat disk, like a medal, or a biconvex lens, sometimes also a biconcave lens. The #Discoidea# can be derived from the #Sphæroidea# by shortening of one axis. This shortened vertical axis is the main axis of the disk; both its poles are constantly equal. Perpendicular to this axis is the equatorial plane of the disk by which it becomes divided into equal halves. In the simplest forms of #Discoidea# all axes of this horizontal equatorial plane (all "equatorial axes" or "cross axes") are equal; in the most of the genera and species these cross axes are different, so that rays of stronger growth ("perradii") alternate with rays of weaker growth ("interradii"). The number of these cross axes distinguishable is commonly two to four, rarely more. In the direction of these are developed either radial marginal spines or spongy arms.

The order #Discoidea# was founded in my Monograph (1862, p. 476) as the family "Discida" (Radiolaria with flat discoidal or biconvex lenticular shell), comprising the {403}"_Calodictya_ and _Lithocyclidina_" of Ehrenberg and a great part of his "_Haliommatina_." As three different subfamilies of that family I separated the Coccodiscida (with five genera), the Trematodiscida (with seven genera), and the Discospirida (with two genera; Monogr. d. Radiol., p. 485). A fourth group of #Discoidea# was constituted by the Spongodiscida (with eight genera, including the _Spongocyclida_), which at that time I united with the Spongurida, because of their spongy structure (_loc. cit._, p. 452).

As the number of fossil #Discoidea# found in the Tertiary rocks of Barbados and of the Mediterranean shores (Sicily and Greece) is comparatively very large, we find even in the first system of Polycystina of Ehrenberg (1847), not less than twelve genera distinguished, viz., six _Calodictya_, two _Haliommatina_, and four _Lithocyclidina_ (Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 1847, p. 53). The whole number of Radiolarian genera distinguished in that first system was forty-four. The diagnoses of them given by Ehrenberg were as usual very insufficient. The characters of the three families given by him were the following:--_Calodictya_--"Testarum intus spongiosarum et nucleo destitutarum orbes; _Haliommatina_--Testæ subglobosæ nucleus radiatus; _Lithocyclidina_--Testarum disci in media parte nucleati margine celluloso." In the latest work of Ehrenberg (1875, p. 157) the same system was repeated, but some new genera added; and thirty-eight different species, appertaining to the #Discoidea#, were figured in the same work (Abhandl. d. k. Akad. d. Wiss. Berlin, 1875, Tafs. xx.-xxx.).

Richard Hertwig, 1879, in his excellent work, Der Organismus der Radiolarien (pp. 57-68), gave a detailed description of the skeleton of some #Discoidea#, and arrived at the conclusion that this whole family had a spirally constructed skeleton, and should therefore be derived from the Lithelida. But this conclusion is certainly erroneous, and in my opinion the whole explanation of that spiral structure, and of its signification in the development of #Discoidea#, is the weakest part of that otherwise very important work.

In my Prodromus (1881, p. 456) I gave a provisional system of the #Discida# or #Discoidea# from the immense quantity of new material collected by the Challenger, and could distinguish not less than eighty-four genera. This number is from subsequent research only augmented by seven, so that in the following pages ninety-one genera with five hundred and one species are described. In the Prodromus I had disposed them in four different families, which number is now increased to six. These six families can be again disposed in two main groups or sections, the #Phacodiscaria# and the #Cyclodiscaria#, each section with three families.

The #Phacodiscaria# are characterised by the possession of a typical "phacoid shell," and contain the three families Cenodiscida, Phacodiscida, and Coccodiscida. On the other hand, the #Cyclodiscaria# are distinguished by the absence of such a "phacoid shell," and contain the three families Porodiscida, Pylodiscida, and Spongodiscida. Both sections exhibit an analogous development.

{404}The #Cenodiscida# (Pl. 48, figs. 1-3) open the series of the #Discoidea# as their simplest forms; a discoidal or lenticular simple lattice-shell encloses a central capsule of the same form, and is separated from it by the calymma or jelly-veil. The common ancestral form of this family is _Cenodiscus_, without radial marginal spines; it can be derived from _Cenosphæra_ in the most simple way, by flattening in one axis. If on the equatorial margin of the lens a peculiar solid girdle be developed, we obtain _Zonodiscus_; in all other genera of the Cenodiscida radial spines are developed on the margin. As the simple lenticular cortical shell of _Cenodiscus_, in which the central capsule is enclosed, is most characteristic not only of this family, but also of the two following families, we call it the phacoid shell (that is, a lenticular extracapsular or cortical lattice-shell).